Duramax compare with the 8.1 litre ?? [Archive]

All-tuned-up

01-21-2003, 14:30

ToughGuy,

Imagine it, we have been testing and comparing, the 8.1 will put the max to rest going up a hill with a heavy load. I have always thought the truck with the torque would have the major advantage when pulling a heavy load up a hill. According to ZFmax, the horsepower is the key feature and the torque does not play into the situation. I guess that's why the old Dodge Cummins that always led the pack that had little horsepower and tons of gut pulling torque did so well? Hmmm.... :eek: :eek: :eek:

PS. I just traded my '02, which was the truck I compared the 8.1 with, not my '03, I realize there is some time for break in there.

As far as the same loads/same roads goes, to some people the extra couple miles to the gallon aren't a big deal. I personally like and think the diesel is the ticket, but an 8.1 getting 8 mpg compared to a diesel that gets 10 isn't really a big deal-especially if he gets up the hill like he is. I have two friends who have the 8.1 and pretty much claim they are unstoppable. We are talking stock to stock now also. Afterall, a guy shouldn't have to cut his airbox up, set his stainless exhaust in the rafters and reprogram the computer to make this diesel dance. I just paid $42k for my truck and hate the fact that a guy needs to make all these improvements, although I will because I'm into all the power available. :D

Dmaxin

01-21-2003, 14:49

Question. Isnt torque the rate at which a motor makes horsepower?

Black Dog

01-21-2003, 15:00

Peak numbers do not tell full the story of an engine's performance. To fairly compare two engines, you need to compare the area under the torque curves. To fairly compare how the engine will pull a load in a given truck, you need to compare the performance of the engine and transmission as a system. Horsepower and torque are two different parameters that both characterize how much work an engine can do. Torque is a measure of force, horsepower is a measure of work. You can do more work with a given amount of torque at a higher rpm.

[ 01-21-2003: Message edited by: Black Dog ]

[ 01-21-2003: Message edited by: Black Dog ]

All-tuned-up

01-21-2003, 15:10

Black Dog,

Would that be why the 8.1 does better at pulling?
With the 8.1 your spinning a much higher RPM, thus creating the peak HP the motor puts out, and utilizing the torque. Whereas, the diesel, when it down shifts, puts the RMP up high and out of the torque range??

Is this what your saying?

Black Dog

01-21-2003, 15:18

Yes, in theory that could be true. That is why the 8100 can make more HP with less torque. I still am not convinced that the 8100 will always win this race though. If the Allison could really keep the 8100 rpms up where the HP is made all the time, yes it would win the race every time. If you look at the Dmax torque curve though, it is very wide and flat - about 500 lb-ft all the way from 1500 to about 3200 rpm. This means that if both trannies upshift at the same time, the Dmax will have an advatage until the rpms climb back up where the gasser is making good torque. I have seen varying opinions on which motor will win the uphill pulling battle, and it may even depend on the exact load and the exact grade of the hill.

SS396

01-21-2003, 15:20

All tuned up, what RPM was the 8.1L running at?

I can only compare my previous stock 1999 6.0L 2500 to my current stock 2003 DMax/Allison. I can haul a 3,100# camper with my DMax up a 6% grade mountain pass at 65mph, 2,200RPM, 4th gear with plenty more. My '99 could also haul that same camper up the same pass at 65mph, but 4,500 - 5000RPM, second gear with none left.

I know the 8.1 is much stronger than the 6.0 (I believe the 6.0 had 300hp, not sure what torque), but that is my only comparison.

Were there possible performance problems with the 02?

All-tuned-up

01-21-2003, 15:49

Black Dog.

It was done with same trailer, same weight on same hill.

SS396.

The 6.0 I think is 280 hp? Not sure, have heard it's an awesome motor. The 8.1 was in tow haul mode, did kick down into third and was revving in 4-5000 range, and the diesel also fell on it's face mid way up the hill into third and was revving up near the red. Your 3100 pound trailer is really not much for comparison. You would be better off pulling that with a half ton, getting a nicer ride and saving a ton of $$ on the purchase. We are talking about pulling a trailer that weighs somewhere around 10-12,000 pounds, this is where you find out really how much power you have. Maybe not enough. :eek:

TraceF

01-21-2003, 16:05

When I joined the DP initially it was to post my concerns (and get feedback) about the lack of performance my new DMax displayed compared to my identically equipped 2000 truck (CC, SB. 4x4) with a 454 and a 4L80E.

In my first post I wrote the 454 would out pull the DMax with the same load, my 10,000+# boat from a dead stop up to any speed. ANY speed. I really thought I would hook up to the trailer and buzz right up to 70 mph and get 15 mpg. Didn't happen, not even close. The DMax could barely take the boat to 60 and I had to hold the pedal to the floor to keep it there.

I still believe the 454 will outrun the DMax with the same load,

But-

The DMax is definitely getting looser as the miles go on. I turned over 4000 today and the fuel mileage is increasing.

I have come to the conclusion that comparing the two trucks is like comparing a quarter horse to a Clydesdale. Also, the DMax "learns" as many of you pointed out. So I run the pi$$ out of it to keep the management systems "alive".

If I run around town for a week and take it easy like I normally drive- the transmission acts differently after a few days. Sometimes I can mash the gas and it won't even downshift. I know the boost is there, my new Banks gauge is telling me 22-23 but no kick down. I'm also confident my truck runs like other DMax's because I bought a GTech and the 0-60 and 1/4 mile times seemed OK for a stock truck.

Also, the diesel will take longer to break in as many have also pointed out. It's just the nature of the design, it's HD !!!

Now, torque vs. HP- torque makes motion (momentum). HP sustains it (speed).

Case in point- work motors generally make more torque than HP as is the case with the DMax. They also usually live longer. Race motors make more HP than torque. They also usually wear out or break sooner. Look at the specs on any overhead single or twin cam engine (import or domestic) or even an outboard motor which is a great example of horsepower technology, needle bearings, etc. and the point is made.

It used to be that the GM big block was rated to pull more than a similarly equipped diesel truck. Why? A combination of both torque and HP I think. Anyone know if this is still true? Diesel vs. 8.1 in the same chassis?

I think break in and time makes these trucks run and perform better but they are still going to be Clydesdales, not quarter horses. They are designed to work and last, not to race. In this design economy of operation is taken into consideration. Shirts and ties writing spec on work trucks care more about fuel economy than gear heads do.

Bottom line- everything is a compromise in some way.

$ .02 more.

[ 01-21-2003: Message edited by: TraceF ]

[ 01-21-2003: Message edited by: TraceF ]

All-tuned-up

01-21-2003, 17:00

Tracef,

That's exactly what a guy here in town has said, his old '97 454 vortec would kill his Duramax in a towing contest.

I think the 8.1 is a monster but everyone else is right about the motor longevity etc. The Duramax that I used against this test was an '02 3500 CC with around 25,000 miles on it. My old '93 did pretty close to what the '02 did.

Thanks for the talk fellas!

I love the max but think the 8.1 has some serious advantages!!

:cool:

billnourse

01-21-2003, 17:49

My Dmax will definately out pull the 1991 454 that I had, and do it easier. I don't know about an 8.1 as I don't have one to compare. There was an article in Trailer Life Magazine about 2 years ago that had the two about dead even in pulling capacity in a test that they conducted.

All-tuned-up,
What was the weight of the trailer you were pulling? On a trip this summer I topped Soldier's Summit between Price and Salt Lake City at 19,440 lbs.total weight at 65 MPH, and had some left.
This pass is mostly 6%+ grade for about 10 miles. On that trip I passed a lot of gas rigs (Unknown engine) that sure seemed to be struggling.

Regards,

Bill

TraceF

01-21-2003, 17:57

billnourse-

The 1991 454 was a throttle body, the 1997 and 2000's are Vortec motors. Big difference.

I would like to read the mag article, do you have any more details?

SoCalDMAX

01-21-2003, 18:03

Hi Guys,

That's an interesting observation about the 8.1L out-pulling the Dmax. I wouldn't have guessed it.

I'd like to put a different spin on it. I paid $33,825 for a 2500HD CC SB LS with everything I wanted (should have gotten 4x4, but, oh well.) For another $700 and 5 mins under the hood, you can add plenty of power. I'm just guessing that $34,500 would be the average selling price for a 8.1L equipped truck with Allison.

I don't think it would be very cheap to modify the 8.1L to get the same power a Juiced (or modded) Dmax gets. I'm pretty sure one would have to change a lot of parts, get very greasy and then wonder if it would hold up for the long haul at those power levels.

I just drove back to San Diego from the desert yesterday. Sea level to 4190ft and back to sea level. With 7,000lb of trailer, I passed EVERYTHING in sight (except the CHP) mostly on the hills, with plenty of pedal left, in total comfort. I was in level 3 and EGTs were 800-1000*, never exceeded 1200*, only hit that for less than a min. at a time.

On a recent trip, my friend's daughter drove his F250 with a 460. I got 10mpg (all uphill or downhill) with all of the toys in the trailer and he got 8 or 9mpg unloaded.

I'm still in awe of this truck. If there was a weakness to be found, I think it's the power handling capability of the Allison tranny. I still think it's the best auto tranny on the market by far, but the capabilities of the motor far exceeds the stock tranny. Fortunately, the vendors are stepping up. :D

PS: I was at the bottom of Oldsmobile Hill in Glamis on Sunday, looking at all of the $50,000-$80,000 buggies and $20,000 race quads. I go over to look at a chromed out Toyota 4 cyl. turbo buggy motor. 550hp on race gas. I start talking to the owner and he turns the topic to.... you guessed it, his Duramax truck. His buddy also has one. Then they ask if I know anyone who's modified the Dmax....

After I get done RITSLMFAO (rolling in the sand laughing my fat a$$ off) I say, "yeah, I might have run across a few of those types." They'll probably join up here after reading for a while. ;)

Regards, Steve

Mic

01-21-2003, 18:34

All-tuned-up ,

Don't take this teh wrong way, but...

1st You said,
"...pulled it up a hill that my duramax would top out at 50, he did it at 75 mph! With room to move.
Anybody did any other comparison's? My max is stock- no chip. What gives?

--------------------

'03 2500 CC/LB Black D/A
Juice Ordered"

but then you said

"The Duramax that I used against this test was an '02 3500 CC with around 25,000 miles on it."

So did you use your 2500 or the 'other' 3500 DRW?

I'm a bit confused on the truck that was used.

:confused:

billnourse

01-21-2003, 18:43

TraceF,

Sorry, I don't have the article. At the time I read it I was not in the market for a new vehicle, so it wasn't a big issue with me. The article has been mentioned on several forums involving RV'S, however I'm not sure where you would find the original article. After I decided to consider a diesel I tried to find the article in Trailer Life Mag. in the archieves, but I think you must have to subscribe to get things like, and it wasn't worth the expense to me, especially since I decided to just take the plunge. So far I haven't been sorry, and I don't think I would go back to Gas.

You also might want to see if you can make contact with Luke S. He posts a lot on the GM Diesel web page, He is a dealer of both Dodge, and Chev, and he does a lot of heavy hauling with both. He might have a bit more information about Gas Vs. Diesel.

The Forum is free. All you have to do is register.

Regards,

Bill

imported_

01-21-2003, 19:14

No contest.... my dodge v-10 modded but n/a would barely outgun my new max...BUT when it comes to mileage it is no contest at all!... now with the juice, that same v-10 gets blown away.....my buddies new 8.1 has no chance against me!

sdaver

01-21-2003, 19:16

My big block truck 8.1/alli 01 would pull the same hills at the same speed as my duramax with the identical trailor..........with the following qualifications.........3rd or 4th gear not fifth and with the tach and the motor screaming........fuel mileage 6 to 7 tops (170 miles and you better be finding some petrol) The same run with the dmax at the same speed or faster 12mpg in fifth..........I really liked the power of the big block and thought I would have to settle for something less with the dmax to gain some economy......boy I was wrong. My 8.1 had a hypertech programer and a airraid cold air intake with a k&n........the dmax had the juice and a k&n with all towing done in level 2 normal juice.
The hypertech and the intake added 20 to 25 rwhp where the juice on that level adds 50 rwhp so say the hp #s are about the same but the torque for the dmax is higher and peaked at a much lower rpm...which in turn would make the truck seem to be in much less of a strain than the 8.1 and it to me was reflected in the mpg........had 99 2500 with 6.0 before the 8.1 it was 300hp factory. I dont recall the torque. It did not have the power like the 8.1 and provided 7 to 8 mpg similarly loaded at similar speeds. Needless to say all of these trucks have their strengths and weaknesses. I still own the 8.1 and the dmax a friend bought the 99. The 99 has 120k miles the 01 8.1 has 67k both run great with no problems(99 lost a abs pump) All three of these trucks have been run hard from the begining but well maintained. I think their durability is a reflection of a good product and design. The dmax has 25k since july and is continually tested daily. I plan to run the dmax myself to 150k until passing it down the line in my company unless the 04's get 6th gear(auto) and 400 hp factory.
:D dave

bluenote

01-21-2003, 19:44

I had a '99 GMC with the vortec 7400, and pulling our 5 ton fifth wheel, the Duramax out-accelerates it hands down if I want it to. I have pulled several grades with the dmax and have found power to spare any time I needed it. It seems like there is a lot of variation in reported pulling power for the dmax at this site, but I can say that mine is all I've expected of it and more for power and performance.

ZFMax

01-21-2003, 22:06

Wow, misinformation about the definitions of torque, rpm, and horsepower, and the relationships between them, still run rampant.

I don't know if I have the energy for this again.

Horsepower alone describes the performance capability of an engine, whether it's accelerating or maintaining a speed against a load or whatever. That's a fact, not an opinion. Any engineer worth the paper his degree is written on will tell you. Hell, forget the degree, anyone who's been through Physics 101 and even came close to understanding the material knows the same thing.

Without going into the whole spiel explaining the why's and how's, just consider a couple of things if you doubt me:

1) When you come to a hill and the truck starts slowing down, can you climb the hill faster at your engine's torque peak or by downshifting and putting the engine at it's horsepower peak? Hint: at the engine's horsepower peak, more torque is available at the rear wheels for a given speed even though the engine isn't making it's maximum torque. The additional rpm of the engine allows additional gear reduction which makes more torque at the rear wheels which more than makes up for the engine's torque.

2) On a more basic level, consider this. Horsepower = (torque x rpm) / 5252, right? You can get this formula out of any physics book. Think about it in relation to the rear wheels. If you keep rear wheel rpm constant (i.e. the speed of the truck), doesn't more rear wheel horsepower mean more rear wheel torque? Doesn't the formula say it has to?

That's as far into this as I want to get sucked. There's a whole big multi-page discussion on it if anyone cares to go read it. You gotta let go of preconceived notions though.

Tough Guy

01-21-2003, 22:56

ZF-

+40HP -70TQ = 25mph???

The Pull-Off will be in June, I will make sure there is a stock 8.1 there... 1 mile, 6% grade, 10,000lbs. The stock Dmax typically runs this hill at 53-58mph, If the 8.1 can run it 78-83mph I'll eat your shoe.

Cheers

Dave

01-21-2003, 23:37

Not 100% sure about the comparison with the 8.1L. I am 100% sure about the compairison with the 7.4L vortec.

My last truck was a GMC 3500 Crew Cab dually with the 7.4L vortec, 4L80E auto and 4.46 gears. I used it to pull my current Travel trailer, a 12,000 pound load. I bought it new, the truck had just over 125,000 miles on it when I sold it. It got 11~12 mpg empty. It got 7.5~8.5 mpg with trailer in tow. Saludia grade would drop the speed to 53mph and the truck would be at red line.

Current truck is Chevy 3500 crew cab dually, duramax, allison auto with 3.73 gears. I bought it new and it now has just over 66,000 miles on it. Pulling the same trailer on saludia I would climb it at 56 mph at 3000 RPM when the truck was stock. The duramax truck get 12mpg towing and 16 mpg empty.

O to 60 mph with trailer was quicker with the duramax. It also did not feel like the duramax was working as hard climbing hills, or accelerating to speed.

Add juice to duramax and it blows the big block away. Saludia is now climbed at better than 63mph and in 4th instead of 3rd with an 2200rpm. I know it would climb it faster if I would push the truck harder.

I have towed extensivly with big block prior to this diesel. I have been pulling RV's for 20 plus years. I will never pull with gas again.

Trippin

01-22-2003, 00:01

Guys,

I spent a few years running a Superflow engine dyno. The formula is correct.

Torque x rpm /5252.

"Torque" is the force. "Horsepower" is the rate at which that force is applied.

With more HP the 8.1L probably did get to the top of the hill at a higher MPH. Screamin it's guts out at 4000-5000 rpm. Pullin that same weight load every weekend to the races is going to wear that gasser out. Start em both off from a dead stop already part way up the grade and I bet the Dmax gets there first. :D

ZFMax

01-22-2003, 00:03

TG, what moves the truck, torque at the engine, or torque at the rear wheels?

Do you know why engine torque and rear wheel torque are different from each other?

Do you understand how an engine with low torque and high rpm can actually put more torque to the rear wheels than a high torque/low rpm engine?

SS396

01-22-2003, 00:16

All tuned up, I agree not much of a comparison.

It is a slide in camper, not a trailer. Need to go in the opposite direction to a 3500, it's 1,000# over GVWR, both trucks. The Dmax only had 700 miles at the time, the performance has since changed/improved. Have since sold the camper, moving to a 10,000# 5ver. I will see what happens when the snow clears the mountains.

All-tuned-up

01-22-2003, 10:05

It's been a fun topic, I'm just a little dissappointed in the 6.6, for the extra $4k the motor costs, you could buy a lot of gas, not to mention the other $850 for the juice. But in the end, after many years, the diesel will be the better ticket.

:D :D

Colorado Kid

01-22-2003, 10:14

Hey tough guy, having pulled "the hill" a couple of times I won't be surprised if the 8.1 does it quite a bit faster...maybe not 78 mph. Why, because in my two pulls the choice was running in the governor at 58 mph or one gear higher at 56 mph and a long way from peak hp (around 2500 RPM and guessing about 250HP (flywheel)). I think chances are very good that the 8.1 can find a gear where it can make more than 250HP...looking at the powercurve from GM Powertrain it looks like any RPM between 3000 and 5000 will get it above 250 HP. My best guess for stock 8.1/Allison with 4.10 rear is 73 MPH at 5000 rpm in 3rd gear. I've been wrong before, but you said it yourself when I was making my second run, the horsepower lives at the top of the tach, and it's horsepower that wins races. :D

imported_

01-22-2003, 10:43

ZFMax

01-22-2003, 16:11

The Colorado Kid is right, that speed difference is much too big to be accounted for by the Duramax's horsepower disadvantage alone.

An 8.1 has only 13.3% more power than a Duramax. 13.3% more power will actually only support 4.3% more speed at a given load. So yeah, if there's a 50% speed advantage on a given load by the 8.1, there's something else going on besides just a horsepower advantage.

His guess that it's falling in between the gearing is probably a good one. I've had that happen to me many times, where I'm pulling the hill and I have the choice of either running on the governor in one gear or running well below the horsepower peak and consequently slowing down in the next gear.

Jelisfc

01-22-2003, 16:49

Morepower, I think the next pull off should include an 8.1 or two. Real life comparision which most of us would accept the results.

My 2 cents... the 8.1 with a 5000 rpm limit simply has more rpm to play with to allow the correct gear combo for max HP.

FightinTXag

01-22-2003, 16:49

Bored at work and I decided to see if what ZFMax says about torque is true.

Dmax at max torque rpm of 1800 in 5th gear is making 178 hp. hp=torque x rpm / 5252

520 ft-lbs
x .71 5th gear ratio
x 3.73 diff ratio
------
1377 ft-lbs @ rear wheels

MPH = (1800rpm x 30.5" tire dia.)/(336 x 2.6483 drive ratio) = 61

If you get it to downshift into 4th you'll be turning ~2500 rpm per the above formula still at close to 520 ft-lbs.

520 ft-lbs
x 1.0 4th gear ratio
x 3.73 diff ratio
------
1940 ft-lbs @ rear wheels

The 8100 at 61 mph in 3rd gear with 4.11 diff ratio is turning 3900 rpms. Being conservative from the graph at the GM powertrain website, the 8.1 makes ~420 ft-lbs at 3900rpms.

420 ft-lbs
x 1.41 3rd gear ratio
x 4.11 diff ratio
--------
2434 ft-lbs at rear wheels.

I had an '01 8100 and I wouldn't ever go back no matter what the numbers say. I usually saw 9-11 mpg unloaded. My spreadsheet says what I paid for the Duramax will be recouped in fuel savings alone in 67000 miles. Any miles after that or any extra resale value is money back in my wallet.

[ 01-22-2003: Message edited by: FightinTXag ]

SteveO

01-22-2003, 16:56

I don't jump in the middle of a fight like this to much, but on this one, I'm going to..

The speed difference is WAY to significant... Something is very wrong...

Did both truck approach this hill at the same speed, or was this a 0 to as fast as you can go hill?

[ 01-22-2003: Message edited by: SteveO ]

Tough Guy

01-22-2003, 17:35

Two years ago at the Pull-Off II, Bill Heath's Dodge Cummins dominated the hill. His truck at the time was making around 350HP and 880TQ with the 10,000lb trailer his speed was 69mph....

As I said earlier, there will be an 8.1 at this years Pull-Off....

Cheers

ZFMax

01-22-2003, 18:15

FightinTXag, that was excellent!

BTW, I agree ... I've been diesel since '92, and I'll never go back to gas. Sure, you can get more performance in some gassers, but the combination of performance, mileage, and longevity make the diesel worth it to me.

Steve Cornell

01-22-2003, 19:18

I had an 8.1 \ Allison \ 3.73 gears and I gross 22,000 lbs with my car hauler..
I now have the same truck in an 03 with the Duramax, although I have not yep towed with the Duramax I really don't think there is much difference in the "ammount" of power, different kind of power yes.

The 8.1 did a fantastic job towing, maybe some of you have towed on this road with simalar loads...
I-77 N.C. \ Va state line (Fancy Gap) very long fairly steep grade (not sure of %) but I could pull the grade at 75 mph grossing 22,000 lbs.

I was pulling this grade in October at 75 and looked over at my wife and said "If the Duramax (which was waiting on me on the dealers lot) pulls even close to this 8.1 you will never get the smile off my face : smile.gif
the 8.1 was running 4000 plus RPMs and sucking gas but I was passing everything in site including several PowerSmokes pulling much smaller trailers.

Once I start towing with the new truck I will give a "unbiased" opinion of the 2 engines.

SS396

01-22-2003, 21:42

Looks like the 6.0L to DMax comparison may be a little closer than we are giving credit.

Using the 6.0L torque ratings for 2002 with FightinTXag's formula:

360 ft-lbs (300HP, 360@4,000
x 1.41 3rd gear ratio
x 4.11 diff ratio
--------
2086 ft-lbs at rear wheels.

Not sure what the ratings were for 1999, nor the gear ratio's in the 4L80E. I think this would help explain my comparison between my '99 and '03.

afp

01-22-2003, 22:22

I know that in drag racing HP is king. My car had a 12-1 roller 350 that dynoed 610 HP at 7000 rpm. The best runs were made flashing the convertor to 6400 RPM at launch and shifting at 8000. I was shifting 1000 rpm over peak HP and at least 2000 rpm over peak torque, and that method provided the quickest times.

I too have my DMax juiced. Most figures I've seen for level 4 are 680 ft lbs at 2300 rpm and 330 HP at 2700 RPM. Using the formula,

680 ft lbs
1.00 fourth gear
3.73 rear end

2563 ft lbs

Drop that to third gear (1.41) and we get 3576 ft lbs.

Even with all that, my money would be on a Vortech equipped 8.1 for the power war. However, it wouldn't be close in gas mileage or longetivity.

Blaine

[ 01-25-2003: Message edited by: afp ]

ZFMax

01-23-2003, 00:50

To do these comparisons accurately, you've got to equalize the speeds like Fightin did. In general, that means the gasser has either a shorter rear axle or it's in a lower gear or both, for the simple reason that it's turning more rpm.

Basically, he figured out that the DMax at 61mph has the choice of 1800rpm (5th gear) or 2500rpm (4th gear) to go 61mph. This nets 1377 or 1940 ft/lbs of torque at the rear wheels, respectively.

The 8.1 by comparison can go 61 in 3rd gear with a 4.11 axle. It can do this because it can turn more rpm than the Duramax. What all that extra gear reduction of running in 3rd and using a 4.11 does for you is it multiplies the engine's 420 ft/lbs of torque into a whopping 2434 ft/lbs at the rear wheels.

The point here is that even though the engine is making 100 ft/lbs less torque than the Duramax, the rear wheels actually have more torque at the same speed. It's able to do that because the engine has more rpm which therefore allows more gear reduction for a given rear wheel speed. His example illustrates perfectly how rpm is every bit as important as torque for performance, because more rpm allows more gear reduction and that makes more torque at the wheels, where it matters.

Because rpm is every bit as important as torque for performance, the total performance capability is a function of the total combination of torque and rpm being produced by the engine, and they're weighted equally. That combination number is called horsepower.

The notion that many people seem to have that somehow horsepower made of high torque and low rpm (i.e. a diesel) is stronger than horsepower made of low torque and high rpm (i.e. a gasser) is pure nonsense. The high torque/low rpm diesel motor has certain advantages, but performance over a gasser of the same horsepower is not one of them.

George Gozelski

01-23-2003, 03:01

Something that everyone is forgetting here, is that a gas engine will lose rpm's faster under a load than a comparable diesel engine. I let a friend of mine who has a dually 1 ton with a 454 in it, borrow my Dmax to tow his boat while his truck was in the shop. He couldn't believe how much better my Dmax towed over his. His truck even had 4:10 rear end gears as compared to the 3:73's in my Dmax! All in all, the 8.1 is a good motor if you're into gassers, but equally matched 8.1's versus the Dmax in a pulling contest (in my humble opinion) is no contest. The Duramax will do the better job.

ZFMax

01-23-2003, 08:56

The rpm is going to drop at a predictable rate when the load on the truck is greater than the force you're putting to the rear tires, regardless of whether the engine has spark plugs or not. It'll follow rule 1 of physics: f=ma. The only thing that affects the deceleration rate, besides the difference in load on the truck and the force at the tires, is the mass of the truck and it's rotating components. So with otherwise equal trucks, the diesel will only lose rpm more slowly if it has more force at the rear wheels and/or more flywheel mass than the gasser.

The force on the rear tires is directly related to the torque at the rear wheels. Torque is twisting force. The definition of a foot/lb is a force of 1 lb applied at a 1 foot radius from the center. So if the tires are 2 feet tall, torque literally is force at the contact patch. With a taller tire, it scales down.

[ 01-23-2003: Message edited by: ZFMax ]

TexasMax

01-23-2003, 09:25

I understand the torque issues. But how will having a turbo or not affect both engines on the same hill?

Stage 1

01-23-2003, 09:51

From my towing experience w/big blocks and Duramax, Trippins comments hit the nail on the head. The Duramax for me is a much better engine to tow with because of it very flat torque and horsepower curve. This is a big advantage over a big block where my driving is up mountains were you need to slow down for curves and other vehicles on the road. My previous big block needed to have speed up before starting up a grade to maintain speed. From a standing start on a grade it could not get out of second gear. Big block was limited buy its peaky torque and horsepower curves (99' 454). (Tow 12 to 13lbs. enclosed trailer.) For my towing needs, Duramax provides more performance. Specifically, ability to drive and accelerate at any legal speed under difference grade conditions, whereas big block could not. The fuel consumption issue is no contest.
I may like the grade braking even better, hardly have to touch the brakes going down mountains!

:D

Colorado Kid

01-23-2003, 09:54

Oh dang! Now I'm gonna have to change my signature after the pull-off...I figured I was going to have to say fastest stock GM, but now I'll have to add Diesel. :rolleyes:

The turbo question is interesting to consider...

The gasser (without a turbo) will loose (FAA rule of tumb) 2%/1000 ft eleveation above sea level.

A typical turbodiesel (before the electronically controlled D-max) would inject fuel at the same rate and continue to make the same power, but higher EGT's and more smoke, as elevation increased. Since it has a MAF (Mass Air Flow) sensor it may trim fuel back to match reduced airflow...on the ohter hand, since the wastegate is evidently controlled by the ECM, and the engine also has a MAP (Manifold Absolute Pressure) sensor, it's possible the the boost is maintained to an abusolute instead of relative pressure (mechanical wastegates open at a specified relative pressure difference, above ambient (local atmospheric) pressure.)...if that was the case the D-max might make very nearly the same power at high elevation as at sea-level...the only decreases being due to higher compression heating of the charge in the manifold...partially mitigated by the intercooler...and higher exhaust manifold pressure do to working the turbo harder (more compressing required to bring lower ambient pressure up to the same manifold pressure). Slower throttle response would also be expected at higher elevation as the turbo plays a bigger and bigger roll in creating power.

I think, but don't know, that the D-max makes virtually constant power at any achievable elevation...there is some point at which the turbo can no longer handle enough air to achieve the goal manifold pressure (critical elevation), and power would begin to drop off. My experiance towing in the Rockies leads me to believe that the D-max throttle response time (turbo lag) is longer at high elevations...also the RPM necessary to develop useful boost increases...but peak power remains pretty much constant. What it will do with a given trailer and grade at 5,000 feet it will still do at 11,000 feet on the same % grade.

The Pull-off location near Missoula is, unfortunately ;) not very high. In the vicinity of 3,000 feet I believe.

baguba

01-23-2003, 15:46

in the atpa truck pulling series,both deisel and gas are around the same horsepower.why then does the sled for the gas trucks have more weight put on it then the deisels? just a thought

JoeyD

01-23-2003, 16:04

I have been to some sled pulls and the diesel class either had more weight or same weight with the sled set to run the weight up quicker.

baguba

01-23-2003, 17:29

according to tom mcconnell- the president of the atpa the santioning body-the gas trucks pull more weight on the sled than the deisels.

X38

01-23-2003, 19:58

I had to chime in on this one. I've pulled over 11,000 miles through Texas, Oklahoma, Kansas, and Missouri side by side with my 2001 K2500 sb 8.1/ZF and my father's 2002 K2500 sb Duramax/Allison(both stock except for the hypertech removal of the speed limiter on the 8.1L). Usually with 40ft. gooseneck flats with various cars and equipment. At interstate speeds the Duramax will not keep up on the hills. I love the Max to death but the big block pulls away(if pushed) from it every time on every hill that we've came across in these four states. The nearly 2000rpm operating range advantage that the 8.1 has over the diesel allows it to run 1 to 2 gears lower than the Duramax at speed. At 80mph my 8.1/ZF can run 4th, 5th, and 6th gears. The Duramax/Allison only overdrive(5th). This is even with the Big Block running 4.10's and the Duramax 3.73's. Yep the 8.1 with the ZF will run 80mph in 4th gear(at the rev limiter), and 104mph in 5th gear(if you up speed limiter). I won't mention 6th. A good example is the grade going east bound on I-44 just west of Rolla, Missouri. With slightly over 14,000lbs behind our trucks and starting the hill at 78mph the Duramax will usually top the hill around 64mph and the 8.1 usually around 72mph.

Is the 8.1 screaming away between 4000 and 5000rpms? yes.

Is the Duramax turning almost 40% fewer rpms? yes

Is the 8.1 drinking gas like crazy ascending hills? yes

Is my fathers Duramax going to being pulling hills well after the my 8.1 is retired? yes

Does the 8.1/ZF that cost almost 7grand less than the nearly identically equipped Duramax/Allison ever get passed by that same Duramax at highway speeds? No

Is my fuel bill about 30%-40% higher than my fathers? yes

Do I smile every time I pass him when loaded? yes

Loaded from a standing start the Duramax will pull away from me until I hit fourth gear, then I catch him.

I'm not saying one combo is better than the other, this is just my own real world experience with these two trucks specific trucks.

[ 01-23-2003: Message edited by: X38 ]

GM Smitty

01-23-2003, 20:34

X38 - That seems like a very nice comparison. Not too many get to run them side by side like that as often as you. Thanks.

NWDmax

01-23-2003, 20:52

X-38's got the best "test" I've seen so far and seems fairly objective on his observations.
One question though :D id you ever swap rigs to see if the driver made any difference at all?
I'm thinking maybe your dad was babying the Dmax or you are a more aggressive driver.
Okay I lied,second question:Whats your top speed in your 8.1 in 6th.I gotta know!
Blake :cool:

George Gozelski

01-24-2003, 01:36

X-38 DOESN'T have the most fair test! I think to make it fair, his Dad needs to install one of the new "boxes" on his Dmax to move the speed limiter up to 3700 rpm, just like his 8.1!

TraceF

01-24-2003, 08:33

X-38's test is interesting.

There have been a lot of comments in this forum about the big block's "screaming" at between 4 and 5 thousand rpm's.

Comparatively, the DMax motors are running at the top of their rpm bands too.

The point I made much earlier in this thread is that the big block has a better working range of horsepower and torque.

I also agree it won't last as long but longevity is a matter of many things including care and maintenance.

My last Suburban had 191,000 miles on it when I sold it (for $5500) and the last two years were 90% hard pulling miles.

That's hard to complain about.

KevinK

01-24-2003, 14:34

A couple of months ago (I can't find the posts) someone was asking about the rwhp of the 8.1l. A reply directed you off to another forum that dealt more with gassers. Anyway, they mentioned several dyno runs and they were all around 260hp. That's not much more than the typical DMAX at 240ish. After serious work (supercharger), one guy was able to get in the 350hp range. That's still not that much.

On a different note, I went from a fairly highly modified 454 (Isky roller cam, Merlin heads, 9:1 compression, Banks Power Pack, etc.) to a diesel and through the Colorado mountains, the diesel would run circles around the 454 (both were pulling ~10,000lbs.). For those who know it, going up the east side of Fremont Pass (between Copper Mountain Leadville) is about as steep as any pass around. The 454 would be down in first, with just enough power to shift into second, but not enough power to maintain it. I would get up the hill screaming at 35mph. My slightly modified Dodge(Power Edge EZ at the time) would go up Fremont at 50mph in third (I'm anxious to try it now ;) ). It's certain that the elevation played a big part (~11,000 feet at the top), but even at lower elevations, the diesel was much better. It will stay in OD long after the 454 would shift into third.

Kevin

[ 01-25-2003: Message edited by: KevinK ]

TraceF

01-24-2003, 16:37

Who let the Dodge guy in?

tongue.gif

KevinK

01-25-2003, 07:24

Here is the link talking about the supercharged 8.1l as well as dyno numbers for a few stock ones.

http://www.gm-trucks.com/cgi-bin/ib3/ikonboard.cgi?act=ST;f=34;t=11267

As for having a Dodge guy sneak in here...Somebody has to keep you guys honest :D .

Kevin

[ 01-25-2003: Message edited by: KevinK ]

TraceF

01-25-2003, 09:02

That's an interesting thread Kevin.

Me thinks you is a plant to be sure we don't pick on the Mopar boys when they ain't around.

We are as honest as the day is looooooong! Seriously. I mean it.

britannic

01-25-2003, 09:30

This thread is really interesting, however one thing that hasn't been thoroughly addressed is this:

The Duramax is the smaller engine at 6.6L and yet can do almost the same amount of work as the bigger, but less efficient 8.1.

The real comparison would be, as previously noted, between the Duramax and a gasser of similar displacement. Imagine if there was an 8.1 Duramax, then the playing field would be level.

If gas engines were the most efficient (even though they can produce more horsepower because of the high rpm advantage), then the nations truckers would be running on gas instead of diesel. ;)

Just my 2 cents.

TraceF

01-25-2003, 16:36

britannic-

Don't think anyone is challenging efficiencies, there is no contest there, we're talking brute force.

It is acknowledged that the gasser will have a shorter life and use more fuel.

I wish I had 2 equivalent trailers in the 5-ton range, I'd stage a pull-off with my 454.

Seat of the pants impression is that from 0-60 or 0-80 or whatever, the 454 would walk away from the DMax easily pulling my 10,000 plus boat.

But again I say, every day the DMax gets looser and I am happier. It will now lay twin 15 foot stripes turning 285's with only about 5 pounds of boost on the brake torque.

Dave says give it 20 pounds but my cajonies aren't sizeable enough. Sure seems like something could easily break with that much torque trying to escape.

:eek:

afp

01-25-2003, 17:43

I guess I have kahonies then, because I have more than once stalled it to 1800 RPM and launched in 4WD. Not sure of the boost as my focus is on the tach. With a G-tech, I got a 5.9 sec O-60 mph time. I imagine a blown 8.1 or 454 could better that.

Britannic does have an interesting point. These comparisons aren't really apples-to-apples in terms of deciding which motor puts out more power per CI. The DMax is 400 cubes and turboed, the 8.1 is 480 cubes and naturally aspitated. To be accurate, we'd need to take a built DMax and compare it with a blown and built 396/402. I still think the 396 would make more power, run quicker, tow better, etc, but it wouldn't last anywhere near as long or get anywhere near the mileage.

Having said that, it appears a "street" blown 8.1 and a juiced DMax are very similar in HP output. the 8.1 winds higher and must geared appropriately. The DMax makes a lot more torque, which is a good thing since it can'r wind as high.

Someone earlier spoke of increasing the Dmax shift points by another 500 rpm and how that would help. I don't think a stock or juiced DMax would benefit from more rpm. My truck--with Juice on 4--definitely slows acceleration as it winds. When it upshifts, rpm drops but acceleration resumes. I think the main reason this happens is because of the way the juice is programmed. Peak HP and peak torque come in lower than it does when factory stock. Now if the fuel curve were remapped, the increased RPM would indeed help and HP would increase.

Blaine

ZFMax

01-26-2003, 10:49

It's great to see that a number of people here understand what the word "torque" actually means, and more importantly, what it doesn't mean, and also how gearing and rpm all tie in.

Eventually, who knows, manufacturers may even be forced to quit trying to capitalize on the confusion through misleading advertising.

mtomac

01-26-2003, 18:19

My duramax replaced a 2000 Chevy 2500 w/454 & 4L80. In stock form the duramax tows a 16000+# enclosed trailer better than the 454. It gets up to speed faster and gets better mileage towing and empty. With the juice on the duramax there's no comparison.

454 mileage
empty 9-11 mpg
towing 5-8 mpg

Duramax
empty 16-20 mpg
towing 8-11 mpg

Steve Cornell

01-26-2003, 22:02

Guys,

There is NO comparison between the 454 and the 8.1, everyone keeps stating that their Duramax outperforms their old 454 (No Kidding??)
Unless you have owned (or at least driven) both the 8.1 and the Duramax you don't really know.

There is no comparison in the economy of the Duramax and the 8.1, the diesel gets much better mileage (no suprise here either) and historicaly the Duramax "should" last longer because of the lower rpms, etc. But that has yet to be Proven!!

Hooking up a trailer and towing up a hill, forgeting about mileage and durability, both the Duramax and the 8.1 are VERY close, I believe on a long pull the 8.1 will outrun the Duramax simply because of the wider RPM range, from a dead stop the Duramax (IMHO) will out pull the 8.1 for a bit but (again IMHO) the 8.1 will pull away after you get it wound.

Yea, add the Juice and then the Duramax wins (again no big suprise) but we are talking about stock vs. stock.....

I love my Duramax and all the "perks" that come along with it, but the 8.1 I owned was the "smoothest" engine I've ever owned and towing there is simply no much that will keep up with it.

TraceF

01-27-2003, 09:58

Michael Tomac- Your words are encouraging. I had the same truck, a 2000 454 with a 4L80E and 4:10 gears. I have only towed the boat once with the DMax and was not impressed but I can tell the truck is loosening up. I got a solid 10mpg empty with the gasser and about 6mpg pulling the boat. I am averaging about 16mpg with the DMax.

Dmax son

01-28-2003, 05:46

Well reading all of this and looking at the other site about the 8.1 supercharger, and then going to the 8.1 fourm here, I think it all has to do with the 8.1 being able to rev higher. In the 8.1 fourm they have a post that showed the 8.1 rear wheel hp numbers at 238, where here guys are saying around 240 for the dmax, and the damx has a lot more torque. Maybe the allison was design to work with a diesel and not the gas and that is why the 8.1 has a 30 percent drivetrain lose that the dmax only has a 20 percent. Reading the other site about supercharging the 8.1, they are paying 5800 bucks for the supercharger, that is more than the upcharge for the dmax, and they are losing gas miliage not to mention extra stress on the engine. I priced what that guy did to his truck, the supercharger 5799.99, headers 759.99, exhuast 305.95, nology hot wires(spark plug wires)est. 200.00, and torque converter 899.99. Oh and various computer changes, that comes to over 8 grand, for 362 rwhp 494rwtq, or 502hp at crank and 686tq. Now take off the upcharge for the diesel 4160.00, That gives us 3805.92, now send mac out with 4000 bucks to spend on the dmax and see how much more power it makes.

Bryan
P.S. If the corvette only loses 18 percent of power thought the drivetrain and the dmax/allison combo only loses 20 percent, it makes me happier to drive it everyday.

MountainMax

01-28-2003, 08:01

KevinK - Do you know where the bridge that crosses the Arkansas is south of Leadville on 24? I'm about 4mi up the mountain in the Aspens looking out at Mt. Elbert.

All-tuned-up

01-28-2003, 08:08

The Question was:

How does a 8.1 compare to a stock Duramax? Not Juiced, no supercharges. Stock from the factory, many people forget one thing about the juice factor when comparing the 8.1, if you run the max w/juice cranked up, how long do you suppose it's going to last. All I was asking is why does my buddies 8.1 literally kill my max in a pulling contest, simple the max has little lug power compared to the 8.1 And all your numbers about torque and RPM don't mean a thing, or slowing down the hill or veering for cars. I'm talking put the foot down and get to the top of this hill without the truck falling on it's face like the max does. I shouldn't have to install a juice on a $42,0000 truck to make it pull something up the hill to have something go wrong and void the warranty. The one guy that runs with his dad has told the story - there really isn't one to tell, his 8.1 puts his dad to shame, sure his dad gets better mileage, he also spent $4,000 or $5,000 more to get that mileage. I didn't buy this truck for mileage, sure it's nice, but I want something that's going to get the truck up the hill without sitting in the embarassing right lane slowing down, especially the way traffic drives/moves now. I think the max is a good truck, just KNOW the 8.1 has way more muscle, and the 454's really don't hold a candle, we'll let them rest now, they have served a good purpose in life, we now have something way better. Thanks for the responses, it's been interesting hearing all the theory's. I'll stick to the road tests.

:D

ZFMax

01-28-2003, 10:40

Well, I stand by my original statement: 340hp is more than 300hp.

Sure, the Duramax has more torque, but torque is not a performance metric. Big torque is just an adjective that says the horsepower is made without turning a lot of rpm. That has advantages, but I don't care how much torque you have, it won't make 300hp as strong as 340hp. That's not an opinion or a theory, that's a fact.

FightinTXag

01-28-2003, 11:01

All-tuned,
If all you cared about was getting up the hill fast while stock, and mileage and longevity wasn't a concern. You probably should've gotten an 8.1L. If you would've driven both, seat of the pants feel, even unloaded, would've demonstrated that.

All-tuned-up

01-28-2003, 15:46

FightTXag:

Show me a dealer who will let you tow 10k #'s with a brand new truck and I would have found my answer.

Seat of the pants feel isn't much difference between the two, I just wish the max would tow like the 8.1 I'm sure it will once juiced, just thought it would have been more comparable to the 8.1

KevinK

01-28-2003, 16:01

ZFMax,

I agree with you 100%. However, I have to believe that the area under the curve is greater for the diesel than the gasser (although admittedly, I haven't seen the curves for either one). If that is true, then the power generated by the 8.1l is greater than the diesel probably in a very small RPM range. Granted, the more gears you have, the more likely you are to be able to find the "sweet spot", but the heavier the load, the harder it is to find.

Kevin

TraceF

01-28-2003, 17:13

Who keeps lettin the Dodge guy in? :eek:

I hate it when they kinda make sense.

The torque/horse power thing has been beat to death here.

Everything has some kind of compromise associated with it. Anyone familiar with term 'piston slap'?

Wonder what the long term opinions of the early 8.1's will be. I'm talking long like the SB and BB GM engines we all grew up with.

ZFMax

01-28-2003, 17:34

Kevin, I think you'll be surprised. Gassers have wider powerbands than diesels, and as such, they typically put more power under the curve of the range they're operated over.

But don't take my word for it. I found these dyno sheets at the GM powertrain web site:

http://www.gm.com/automotive/gmpowertrain/engines/duramax/apps/images/dmax_curve.jpg

-and-

http://www.gm.com/automotive/gmpowertrain/engines/vortec/apps/vehicle/images/l18curve.jpg

Let's assume both motors get wound out to their power peaks of 3000rpm and 4200rpm respectively. Yeah, I know, area under the curve is greater if you take'em past the power peaks, but we don't have that data, the charts basically end at the power peaks. So let's go with that, it won't skew the results if we apply it equally to both.

Let's go with the Allison since that's the most popular choice. First gear is 3.10. So what happens when we wind out each motor to it's power peak and change gears?

1st to 2nd: the 2nd gear ratio is 1.81. The new rpm will be 1.81/3.10 = 58.4% of the old rpm. Therefore:

- The Duramax will go from 3000rpm down to 1750rpm. From looking at the chart, the power will drop from 300hp down to about 170hp.

- The 8.1 will go from 4200rpm down to 2450rpm. From looking at the chart, the power will drop from 340hp down to about 200hp.

2nd to 3rd: the 3rd gear ratio is 1.41. The new rpm will be 1.41/1.81 = 77.9% of the old rpm. Therefore:

- The Duramax will go from 3000rpm down to 2340rpm. From looking at the chart, the power will drop from 300hp down to about 230hp.

- The 8.1 will go from 4200rpm down to 3270rpm. From looking at the chart, the power will drop from 340hp down to about 300hp.

3rd to 4th: the 4th gear ratio is 1.00. The new rpm will be 1.00/1.41 = 70.9% of the old rpm. Therefore:

- The Duramax will go from 3000rpm down to 2130rpm. From looking at the chart, the power will drop from 300hp down to about 210hp.

- The 8.1 will go from 4200rpm down to 2980rpm. From looking at the chart, the power will drop from 340hp down to about 275hp.

4th to 5th: the 5th gear ratio is 0.71. The new rpm will be 0.71/1.00 = 71% of the old rpm. Therefore:

- The Duramax will go from 3000rpm down to 2130rpm. From looking at the chart, the power will drop from 300hp down to about 210hp.

- The 8.1 will go from 4200rpm down to 2980rpm. From looking at the chart, the power will drop from 340hp down to about 275hp.

Now this isn't an exact comparison because to really calculate area under the curve, you've got to integrate. I mean, it's possible that one motor could be higher at these two data points and yet have less area under the curve. But both of these hp charts are pretty damn linear, heading up and to the right. In fact, the 8.1's is fatter since it's torque curve isn't as flat, the data points all fall on each side of the torque peak. So if it's winning at both data points, which it did on every single gearshift, it has to be winning in area under the curve as well.

KevinK

01-28-2003, 18:35

ZFMax,

Thanks for putting all the effort into gathering real data. That's certainly more convincing than my speculation. I am surprised, to tell you the truth. I expected the 8.1l to be really peaky compared to the Duramax. I guess that's a good argument for cubic inches. Anyway, I'll stand by my earlier statement that I agree with you 100%!

Kevin

Tough Guy

01-28-2003, 19:29

Check this out:
http://www.trailerlife.com/test/0010v8.cfm

Scroll down to where it says "HARDWARE DETAILS"

*Note the Dmax is 1000lbs heavier, and the RPM to peak HP and speed between the two pulling, and the 0-60 times loaded....

The pull-off will be interesting......

Cheers

afp

01-28-2003, 22:28

How long will a DMax last with the Juice cranked up? Longer than the 8.1 will sustaining 4000-5000 rpm. RPM is what kills motors. Especially one with as much rotating mass as the 8.1.

Interstingly enough, the Edge guys say the reason the DMax runs so hard with the Juice isn't because of the extra 250 ft lbs of torque it makes, but it's because the thing makes 200 HP at 2000 rpm. Yes, it does make a total of 330ish HP at 2700ish rpm, but what accelerates it is that 200 HP at coming in at 2000 rpm.

We still haven't fully explained the torque vs HP thing. HP tells us how much power is being made. However, when were talking about transmission life, we talk in terms of how much torque it can take. We know all the standards--450 ft lbs for a beefed 700R4, 750 ft lbs for the Allison, etc. Why aren't we concerned about HP tearing up trannies?

I personally don't see what all the fuss is about between the 8.1 and Dmax. As long as I can remember--and much to the consternation of the diesel guys (who I am now one of)--a big block gasser has always had more ultimate power potential than a diesel. It is not hard to get 900-1000 streetable HP out of a big Chevy. The diesels were usually more durable and got better mileage.

The issue seems to be which truck is better? There is no answer. I bought my DMax because I wanted a truck that would last 20 years and got decent gas mileage in a crew cab configuration. I am the kind of guy who buys something, then takes it home, takes it apart and makes it better. I didn't spend a lot of $$ making my DMax better, and to get equal power from an 8.1--as has been pointed out--I would need to spend more than I have in my DMax, I'd get lousy mileage, and I'd wear the thing out. On the other hand, I fully believe I can get more power out of the 8.1.

If my folks had the money, they'd buy the 8.1. It would have nothing to do with performance, but my mom just doesn't like the smell of diesel. maybe she has the right idea. Buy what smells best to you..........

6 2 Carl

01-29-2003, 02:19

I have been watching this thread for a while, and I have to add my two cents. Although I haven't towed with an 8.1 or Duramax, I did spend my summers trucking, while I was getting my mechanical engineering degree.

One summer I had a dedicated run that I must have ran over 40 times. The trip only about 600 miles but it was very hilly, with grades up to 9%. I made that run with all 5 trucks in our fleet which ranged from 350 to 450hp and 8 to 13 speed transmissions. The trips were usually made in convoys of 3 or more trucks, so it made for some very interesting comparisons.

While there is no denying that the 450hp truck had the potential to make it to the top of the hills the fastest, that wasn't always the case. It came down to how the truck is driven. By the end of the summer I had those hills down to a fine science. I knew when and where to make shifts, and at what rpm's to make it. I drove the trucks very hard and was squeezing every ounce of power out of those trucks, but the result was that 95% of the time I was the fastest up the hill regardless of what truck I drove.

So my first point is that it is that proper driver input is needed to extract maximum performance out of a truck, and this can be a big factor when comparing the pulling performance between two trucks.

My second point comes from George Gozelski's quote "Something that everyone is forgetting here, is that a gas engine will lose rpm's faster under a load than a comparable diesel engine" For the most part diesels do hold speed better on hills do to torque rise. Consider this hypothetical example:

Two identical trucks one with a Duramax and one with an 8.1, both with ZF transmissions, and pulling the same load. The trucks are traveling at 70 mph, at this speed, only 125hp is needed to overcome wind resistance, so either truck has no problem pulling the load in sixth at about 2100. The trucks come to a moderate hill, and start to loose a bit of speed. Since the torque peak of the Duramax is at 1800rpm, it pulls harder the closer it gets to its torque peak. Wind resistance decreases as the truck looses speed and eventually the truck will slow to a speed where the force applied by engine is the same as the forces applied by the load. The 8.1 is on the other side of the torque peak which is at 3200rpm. As the truck slows it the torque is also decreasing, so it will loose speed faster, and continue to loose speed until a downshift is made. This is one of the main reasons people enjoy towing with a diesel since there is less downshifting on moderate hills. Most people don't mind loosing a few mph on a hill, if it saves a downshift. Remember how everyone hated the shift business of the Alison when the first Duramax trucks came out?

To summarize my second point: Maximum power is not needed while traveling on flat ground, so most people run in the highest gear and lowest rpm in order to get the best mileage. Unfortunately this puts most gas engines on the wrong side of their torque peak. This means the 8.1 will always have to downshift before the Duramax, when a hill is encountered. This gives the perception that the Duramax is more powerful, but the fact is the 8.1 is just running outside of its powerband.

I know I have just reworded many points that have already been brought up, but this is my take on this issue

Carl

[ 01-29-2003: Message edited by: 6 2 Carl ]

TraceF

01-29-2003, 08:04

Tough Guy- The 1000# difference is hard to buy. The reason I say this is that my 2000 K2500 4x4 CC SB scales with me in it at 6460. My 2003 HD2500 4x4 CC SB scales at 6980. That's 520 more and looking at the frames in comparison it is hard to believe the K2500 is heavier without the drivetrain.

:confused:

The scaling was done at the same location.

KevinK

01-29-2003, 09:25

MountainMax,

I know exactly where you are talking about. It's a beautiful area up there. We go up to Turquoise every year, so we've been around that area a fair amount. It's great that you are able to live up there.

Kevin

I was going to give you a PM, but they don't seem to allow that here, like they do on the TDR ;) .

[ 01-29-2003: Message edited by: KevinK ]

Bulldogger

01-29-2003, 10:34

I've owned and towed with both. The 2001 8.1l dually and 2003 duramax dually both had the allison. I towed my trailer, an 11000 lbs American Star 5th wheel, down to Florida with the 2001 8.1 and towed the same trailer back to New York with the 2003 Duramax which I bought in Florida. Stock to stock, there is a noticable difference between the two. The 8.1 is faster towing and runs a higher top end with trailer in tow. The real difference is in how they tow. Alot is driver precieved. The top speed achieved isn't as significant as to how differently the trucks respond. Towing with the gas, the throttle is much more responsive to driver input, step on the peddle, get a down shift and hear the RPM's screamin and you know your moving.The diesel traveling at 65 step on the pedal and it drops to the floor without a down shift, no RPM change, and is basically pedal dead. You need to stomp the pedal or take it out of overdrive to get the truck moving and even at that point, it's still much less responsive. The change off is that the diesel is quieter in the cab than the 8.1 climbing a hill. The diesel very rarely drops out of overdrive vs. the gas motor which shifted constantly and runs right to red line. Plus with the gas motor we stopped nine times for fuel and with the diesel we only stopped four times. So the fact that the gas motor tows faster really doesn't matter much because with only half the stops for diesel fuel I managed to shave 1 hour off the full trip. So what you gain in top end speed you loose over the course of the trip to gas stops. But to answer the original question the gas motor is faster and more responsive towing a load than the diesel.
Thanks
Dave
PS Let the attacks begin! smile.gif smile.gif smile.gif smile.gif

mdrag

01-29-2003, 11:24

I think it all depends on your driving style. From what I've personally observed, owners of gassers tend to drive with the seat all the way forward, and diesel owners drive with the seat all the way back ;) ...and we all know how doggy the Dmax is with the seat all the way back :D :D

This is an interesting topic that has brought up many great points (mine excluded). I was looking for a truck when GM came out with the 8.1L and Dmax. Motor Trend awarded the 2001 2500HD the TOTY, and that article convinced me to rethink my decision to buy the 8.1L. I'd never owned a diesel.

In the MT testing, the 8.1L put up better performance numbers, but the fuel economy was horrendous compared to the Dmax... From my previous experience adding power to turbo vehicles - I knew it would be easier and cheaper to add power to the TC vs NA engine. So far, the Dmax has far EXCEEDED my expectations and IMHO well worth the price of admission :eek: and keeps getting better...

I realize this is discussion of stock vs stock performance, but since I did not intend to keep mine stock forever, the unmodifeid performance of the 8.1L vs Dmax was irrevelant to MY decision to buy the Dmax.

It'll be intresting to see the results of the next Pull Off if Tough Guy rounds up a stock 8.1L for comparision...

[ 01-29-2003: Message edited by: mdrag ]

FightinTXag

01-29-2003, 13:39

TraceF - The Duramax in the comparo was a crew cab/sb while the 8.1L was an ext. cab/sb. That along with the extra weight of the diesel could account for close to 1000 lbs of extra weight, I opine.

All-tuned - My 8100 felt monstrously faster than the Dmax unloaded. The 8100 would light up the tires by mashing the go pedal, no brake. My duramax won't. That seemed to add to the perception that the 8100 was faster. Maybe most of my seat-of-the-pants runs were from stoplight to stoplight and the Dmax suffers from turbo lag. That along with the fact that the 8100 was a short bed 2wd and the Dmax is a long bed 4wd probably put the Dmax at a further acceleration disadvantage.

TraceF

01-29-2003, 15:05

From Bulldogger-

<<The diesel traveling at 65 step on the pedal and it drops to the floor without a down shift, no RPM change, and is basically pedal dead. You need to stomp the pedal or take it out of overdrive to get the truck moving and even at that point, it's still much less responsive.>>

This is exactly the driving impression I got when I towed the first time with the DMax after pulling so long with the 454.

Even now, going along at 65 unloaded the truck will sometimes not downshift.

Is this a transmission issue?

DmaxMaverick

01-29-2003, 17:45

"Even now, going along at 65 unloaded the truck will sometimes not downshift"

If the cruise is on and above 50 MPH, it will not downshift for several seconds IF there is not a significant increase in speed, with either driver input, or aproaching a hill/overpass. The downshift is inhibited by programming with cruise on. This was changed about midway through the '01 MY, due to complaints of it downshifting with cruise on in OD.

X38

01-29-2003, 20:43

Heck,

If you guys need a stock 8.1L for the pull off I'll bring mine. I don't know if you would rather have the Allison but if the ZF combo works for your tests, then I offer. Heck, I might just load the old man's Duramax on the gooseneck and bring it as well. Where's the pull-off and when is it? Have food. Will travel.

Someone asked earlier what top speed I seen in 6th. So far I have seen 4000rpms in 6th. External factors cut that run short. I'll let you guys do the conversions. :)

Great thread. Thoughtfull insight with little B.S. You guys make this sight a pleasure.

Stage 1

01-29-2003, 20:58

Trailer Life magazine did a road test of both the Duramax and 8.1 gas engines, which included towing a trailer. In some cases the gas engine performed better and in others the Duramax performed better.
Specifically the DMAX out performed the 8.1 in towing acceleration 0 to 60 MPH, 40 to 60 MPH. The respective times for 0 to 60 were 30.3 secs - 8.1(25% more time) and 24.4 secs - DMAX. For 40 to 60 16.4 secs - 8.1 (26% more time) and 13.0 secs for DMAX.

This data shows that the DMAX has more something under the curve for certain performance tests.

Which engine is better is a individual choose. Key is to provide good information for use in making decision.

For me, the DMAX is what I want for towing my C/SA GSX.

MountainMax

01-30-2003, 09:53

KevinK- e-mail me Mtnguyd@ev1.net

All-tuned-up

01-31-2003, 15:37

Bulldogger; thanks for the reply, it's just a big race over here and everybody is trying to outdue everybody. A good friend of mine was extremely close to trading his '02 CC D/A in for a '03 same truck witht the 8.1 let's just say he's not the easiest guy on equipment. Ok, so he's a fool. He is just not satisfied with the duramax, thinks the 8.1 would be a better truck for him, he tows a bobcat around and he drives like hell on wheels, always 80 on the freeway, he's getting 13 and that's not good enough for him. His cousin has a 8.1 with Amsoil air intake, and claiming he's never gotten worse than 9, mostly 12 on hwy. I don't think the guy can divide! I can't talk him into a juice module, for whatever reason, he's worried about warranty. He's one of those that knows it all. I bought my duramax for the power and the mileage, I'm waiting on a refurbished juice mod, if I ever get it is another story. I'm just can't wait to see if this SRW will get better mileage than my '02 dually did. Oh, he's also had to have the pump pulled and new one put in, it went bad right away, the other day, -10 out and his duramax wouldn't start, no he really hates the truck. Said he had to prime the pump. Dealer told him to run straight number one, we're like, no I don't think that's the answer. I told him to change the fuel filter, he said "the truck only has 14k on it, the manuaul said you can wait to 20k" I said, not! You might have picked up water or bad fuel-change the filter tight _ss.

Thanks for all your replies, it's been a wealth of information.

Love the website, just hope my boss doesn't figure out how many hours I'm on it per day, and he's paying me?? :eek: :eek: :eek:

Bulldogger

01-31-2003, 22:27

All Tuned Up, I drove my 8.1 down to Florida with the 5th wheel in tow and driving at about 60-65 I was averaging 5.9mpg. The truck unloaded never gave better then 10.5 on the highway.The 2001 dually was a crew cab with 4.10's and limited slip rear. The trucks tow very differently but I have a refurbished juice that I'm putting in the diesel, an Amsoil 2-stage filter already in,the spa DG-211a combo gauge is sitting on the fire- place mantel. Only thing left is the exhaust, I'm leaning towards the ATS stainless dual exhaust with matching 5" grapefruit shooters on each side.Even with the Juice and towing at 75 I'm pretty sure the diesel won't drop down to 5.9mpg and even if it does it won't matter because my wife will kill me on the spot anyway. The 2001 8.1 had the Granetteli MAF and the K&N FIPK kit.That add on stuff made no noticable difference pulling except for rasing the cabin noise on hill pulls. I'm hoping that all the mods to the duramax will give me the pulling feel of the 8.1 with the economy of the diesel. AAHH to have a dream is a wonderful thing. Dave

Lower_Suburbia

02-04-2003, 23:32

Interesting posts I have to agree with 6.2 Carl Driver input makes a big diff. I just wish I could get a Dmax and Zf in a 90-91 Suburban with Duallies and a 2 speed rear end. Not that would be a tow vehicle for me.

LittleBigRig

02-17-2003, 20:13

Seems to me we're all forgetting about one big variable: the turbo.

A turbo charged engine will tend to maintain a more constant power profile than a naturally aspirated engine at higher altitudes. As air density goes down, waste gate and electronic management controls will increase the boost to compensate.

It seems to me the question that you need to be asking when you compare the gasser to the smoker is "what altitude were you running at?" My guess is that the difference at sea level is probably much less pronounced than say at a 7000 foot mountain pass.

Diesel Freak

02-17-2003, 23:55

ZFMAX posted 01-28-2003 09:40 AM:
I stand by my original statement: 340hp is more than 300hp.

Sure, the Duramax has more torque, but torque is not a performance metric. Big torque is just an adjective that says the horsepower is made without turning a lot of rpm. That has advantages, but I don't care how much torque you have, it won't make 300hp as strong as 340hp. That's not an opinion or a theory, that's a fact.

By that rationale, I should change the 330hp Cummins in my Freightliner to a 340hp 8.1. Let's even supercharge that 8.1, make it a 500hp monster, then I can really move that 80,000lbs up the mountains. :rolleyes: Don't discount torque, you're right to a point, but when you get into BIG torque #'s, it's gonna get that load up the hill. That's not an opinion or a theory, that's a fact. ;) tongue.gif

Duramaxerado

02-18-2003, 00:01

excellent post diesel freak!! smile.gif

[ 02-17-2003: Message edited by: Duramaxerado ]

imported_

02-18-2003, 00:08

the common conversion factor of most sanctioned racing that involves both turbochaged gas and n/a gas engines it 1.4 therefore a 6.6l duramax diesel they would class it as a 9.24 liter engine but with the weight involved i am sure that the formula would be more like 1.2 correction factor.
also it is a diesel not a gasoline engine.
I originally puchased the diesel for towing and i am very impressed with my duramax. the juice just takes all that goodness to the next level.

ZFMax

02-18-2003, 11:52

Dieselfreak, there's an amazing thing about the laws of physics: they just keep right on doing the same thing even when people don't understand them. Make up all the nonsensical definitions you want, doesn't change a thing.

Redhawk

02-18-2003, 12:30

As a kid growing up in Southern California, the bible for those who wanted to go fast was, of course, Hot Rod Magazine. Their number one rule, all things being equal, was "there is no substitute for cubic inches". Their number two rule for going fast asked "how much do you want to spend?"

Diesels were not mentioned in either equation, but I'm sure some of that advice rubs off as concerns my Duramax. If you are asking a 6.60L engine to out-perform an 8.1L engine, INHMO you are asking too much from the diesel. Granted, the turbo-diesel narrows the difference somewhat, but the gearing is not the same either, so the gasser should still win every time.

That would be true on the flat, and on hills below 5000 ft or so, but once the game is shifted to altitude the turbo might narrow or exceed that difference. So overall the larger displacement engine should outperform the smaller engine.

Once you start adding performance equipment to the diesel to catch the gasser nothing is really proven about whose truck is faster up the hill unless both trucks have the same "improvements".

Rule three should be: "drive the truck that suits you", and quit worrying. For me, I'll keep the Duramax. It's been far more truck in every way than any gasser,OR diesel I've ever owned so far. All that having been said, I stlll read all the "improvement" ads for diesel engines.

Tough Guy

02-18-2003, 19:31

ZF-

Check this out:

http://www.trailerlife.com/test/0010v8.cfm

Scroll down to where it says "ACCELERATION"

**Note the Dmax is 1000lbs heavier, and towing the Dmax beats the 8.1 in 0-60 and 40-60......With less HP how in the world does it do this? Now imagine if the test would have included 0-60 and 40-60 on a 6% grade........

Its NOT just about HP. ;)

Cheers

Diesel Freak

02-18-2003, 19:55

ZFMAX, I certainly hope you are not foolish enough to try and tell me and everyone else on this sight that a 340hp 8.1 motor will out pull a 330hp M-11 Cummins engine, please say it ain't so!! There's a funny thing about physics as you say, guess what, TORQUE DOES MATTER! I'm not going to get into a p*ssing match with you. I'm sure every person will agree that torque is a huge factor when it comes to moving huge loads. Certainly a pickup with an 8.1 is going to be faster than my Freightliner EMPTY, but it doesn't stand a flippin chance grossed out at 80,000lbs. Reguardless of how many gears at whatever ratio you give the pickup, it's JUST NOT GONNA HAPPEN!

When I posted my earlier comment, I was joking, I can't believe you are actually challenging me. I'm not trying to be nasty, but come on, obviously torque is a HUGE factor.

ZFMax

02-19-2003, 09:45

Well Dieselfreak, it's like this: geared for the same rear wheel speed, more horsepower = more torque at the rear wheels.

I don't care if one motor has 1000ft/lbs of torque and the other has 10ft/lbs of torque. If the motor with 10ft/lbs has more horsepower, and you gear both motors for the same rear wheel speed, the 10ft/lb motor will have more torque at the rear wheels.

That's not an opinion, it's a fact that's very simple to prove. To deny it is just silly and ignorant.

If you want to understand why this is true, I'll help you. But you need to let go of your preconceived notions of what the words "torque" and "horsepower" mean and how they're related, because it's apparent that you don't understand them.

Let me know if you're interested. If not, and you prefer to live in denial, that's cool too, I'm not concerned.

[ 02-19-2003: Message edited by: ZFMax ]

Steve Cornell

02-19-2003, 17:53

Hey !!! I've got an idea !!! :D

I know this will never be a replacement for all the great torque vs HP theory.. ;)

But lets take 2 identical trucks (one a Duramax \ one a 8.1) both stock with the same load and pull the same hill side by side and see who gets to the top first :rolleyes:

I know this is not very scientific but it may give us the much sought after answer ;)
but if one beats the other I'm sure there would be something not fair as something must have surely not have been right with one of the trucks so we would need 3 of each truck for a complete comparison.

LOL. just joking around.....

I had a 01 8.1 and now I have an identical 03 Duramax (same gears 3.73) and while the Diesel is not even yet broken in it seems to me that the 8.1 would slightly outrun the Duramax empty, I do have data though from several past trips pulling my 15,000 lb car hauler and I'll be making a trip to Florida next month with the same load and I'll post my "unbiased" results when I return.... of coarse even though this will be the same load at the same weight on the same highway it may mean nothing unless the temp. and humidity are exactly the same, right ?? LOL :D

Just remember.... my trucks ALWAYS faster than yours :D

EWC

02-19-2003, 19:20

OK ZFMax , I'm interested in learning what you mean by HP and torque . Please use the correct terminology so that I can follow along . I'll start : torque is measured in lbs/ft not ft/lbs . Most people use ft/lbs , this is a misnomer . I also thought when you dyno an engine , you measure torque and calculate HP . Can you help me ??

Diesel Freak

02-19-2003, 21:26

okay, ZF, I'll bite, explain to me how a 340hp / 420 lb/ft torque 8.1 liter gas engine is going to pull 80,000lbs up a 6% grade better than the Cummins M-11 330hp / 1400 lb/ft torque engine? I can do that at 1800 rpm and 43mph. You tell me exactly what kind of gearing it is going to take for that 8.1 to do the same thing, only better?? Come on guy, we all know it's not possible. I understand what you are trying to say, and as I said earlier I was merely joking until you challenged me. There is absolutely no way that a motor with nearly 1000 lb/ft of torque less is going to out pull the other motor at the same speed just because it has 10 more hp. REGUARDLESS of the gearing. Just like the 200hp engine in my Ninja sure isn't going to out pull the 195hp 6.5 GM.

orange2

02-19-2003, 23:55

diesel freak, you got a zx 12? I do, ain't they fun!!

ZFMax

02-20-2003, 00:18

Okay DF, here goes. Let me know the FIRST statement you have a hard time with, that'll help me zero in on where you're confused:

1) If the Cummins M-11 is making 330hp @ 1800rpm, that means it's making 962.867 ft/lbs of torque.

2) The Chevrolet 8.1 is rated at 340hp at 4200rpm. That comes out to 425 ft/lbs of torque.

3) Let's say both trucks are geared for 50mph with the same 28" tall tires. With a 28" tall tire, 50mph is 600 rear wheel rpm.

4) To gear the Cummins for 600 rear wheel rpm, we have to apply 3:1 overall gear reduction. 962.87 ft/lbs or torque at 1800rpm from an engine, geared 3:1 overall, results in 2,888.6 ft/lbs of torque at 600 rpm at the rear wheels

5) To gear the Chevrolet for 600 rear wheel rpm, we have to apply 7:1 overall gear reduction. 425 ft/lbs or torque at 4200rpm from an engine, geared 7:1 overall, results in 2,975 ft/lbs of torque at 600 rpm at the rear wheels.

6) 2,975 ft/lbs of torque at the rear wheels of the Chevrolet powered truck is greater than 2,888.6 ft/lbs of torque at the rear wheels of the Cummins powered truck. With the same tire size, it's capable of pulling more load.

Like I said, let me know the FIRST statement you have a hard time with, and we'll work on that.

EWC: The definition of a foot/lb of torque (not to be confused with a foot/lb of work) is 1 pound of force applied at a 1 foot radius. Whether you say it that way, or say a 1 foot radius with 1 pound of torque applied, makes no difference. I checked my old dusty college textbook and it refers to torque in ft/lbs.

Yes, you are correct, a dyno works by measuring torque and rpm and calculating horsepower. There are two popular types, the "brake" dyno and the "inertia" dyno. They do it slightly differently but that's the general idea.

Generally a water brake or eddy current brake is used in conjunction with a strain gauge. So it measures the torque directly. The inertia dyno by comparison extracts torque by measuring the acceleration rate of a drum of a known mass.

Diesel Freak

02-20-2003, 09:01

Okay ZF, here we go, I understand how you are calculating torque based off of HP and RPM. The problem I have is you are saying the Chevy will out pull the Cummins, I got a fistful of cash to bet on that one :D But seriously, the ratings on Cummins websight for a ISM (I couldn't find the M-11) is 330hp (no given RPM) and 1350 lb/ft of torque at 1200 rpm. Did you actually say, or did I misunderstand you, that the Chevy will outpull the Cummins if it had the correct gearing? That's what I have a problem with, it's just not gonna happen. Now maybe you can sit there and run all sorts of calculations @ rpm, gear ratio, wheel speed etc. And have it look good on paper, but the fact is, no chevy pickup, reguardless of gearing is going to outpull a semi, period. That's my only point. Obviously this is because although the semi has slightly less HP, it has a tremendous more amount of torque. We can't really sit here and argue that fact. If the Chevy motor was capable of pulling better, obviously it would be in a semi for a savings of $10,000 or more. My point was not to sit here and argue math and physics with you, any monkey with a formula and a calculator can do that. tongue.gif All I was merely trying to state, rather tongue in cheek, is you guys are talking about a pull off of the 8.1 vs. the Duramax and how the 8.1 will win because of more HP. I want to bring my Freightliner to put it up against the 8.1 chevy. We all know the Chevy stands no chance whatsoever, which is why my original post was started as a joke. If you still feel your chevy can outpull my Freightliner, heck, let's put some money on it. How about 10 grand? :D tongue.gif :eek:

So ZF, why don't we shake hands and part as friends. This is really getting silly.

PS. I'll bring the beer to the pull off!
;)

svpdiesel

02-20-2003, 14:31

DF- No offense, but ZF is right as far as the big block out running the Cummins if the 8.1 is geared right. What ZF is trying to get you to see is the fact that, if the 8.1 was dropped into your freightliner, it would be running many gears lower and at a much higher rpm, and yes, putting more power to the rear wheels. If you put both engines in the same gear, same rpm, the cummins will win because it makes more HORSEPOWER at LOWER rpm. The reason they don't put 8.1's in Freightliners is mostly that the 8.1 will not last long running at max power, but the Cummins will.

Tsckey

02-20-2003, 15:55

I must say, I love this topic every time it rolls around. I have learned a great deal from ZF and thank him for his patient, thorough explanations. Initially, I shared DieselFreak's consternation about the image of a piddly little gas motor out performing a massive, high-torque bull diesel. The image of my little, 150hp Toyota 4Runner performing right alongside an early Cummins pickup seemed pretty incongruous. I could barely get my middle sized tent trailer up hills without the Toyota screaming its lungs out. My friend used to tow enormous sailboats with the Dodge. But, physics, is physics. These laws of nature are not affected by opinion, they just are.

Gradually, I began to understand what ZF was talking about. He's talking theory, very doable, practical theory and he's right. He explained how the 8.1 could out pull the big Cummins and this is not his opinion, this is an immutable law of the universe. The engineers who design and build heavy haulers know and understand the same phenomona. There is a reason they choose to configure their trucks the way they do. They need to factor in not only the ultimate performance characteristics of the machinery they are designing, but also the nature of the work it will be called on to do and the manner in which that work will be performed. Looking at the requirements of economy, durability, and drivability they choose the big, heavily built slow turning diesels with a bunch of gears to do the work over the high winding gassers. They are right, too.

DieselFreak, I'd withdraw that offer If I were you or ZF will be buying his wife some expensive Christmas presents with your money.

TC

2K2AD

02-20-2003, 16:10

TC,

Well said! I have also enjoyed this topic whenever it rolls around. I appreciate everyone's (esp. ZF's) time. Keep up the great work, guys!

Kevin

ZFMax

02-20-2003, 16:12

"I understand how you are calculating torque based off of HP and RPM."

Well, um, that IS the formula after all. Torque = (horsepower x 5252) / rpm. Ignore the engine for a minute. Just looking at the rear wheels only, 330hp at 600 rear wheel rpm comes out to less torque than 340hp at 600 rear wheel rpm. If you believe the formula, then you also believe more hp = more torque at a given rpm. That's exactly what the formula says.

"The problem I have is you are saying the Chevy will out pull the Cummins, I got a fistful of cash to bet on that one"

The problem with that bet is that we'd have to essentially move a Cummins motor to a Chevy (or vice-versa) and make gearing changes to be able to do the comparison. Otherwise the loads won't be the same and they won't necessarily be geared for the same speeds.

"But seriously, the ratings on Cummins websight for a ISM (I couldn't find the M-11) is 330hp (no given RPM) and 1350 lb/ft of torque at 1200 rpm."

1350 ft/lbs of torque at 1200 rpm is 308hp. So that data point is the torque peak, not the horsepower peak. If we do the comparison at the Cummins' torque peak instead, it needs 2:1 gear reduction to get to 600 rear wheel rpm, and that puts 1350 x 2 = 2,700 ft/lbs of torque at the rear wheels versus the Chevy's 2,975. So it loses by more. The horsepower peak is always the point where the most torque reaches the rear wheels when geared for a given ground speed.

You didn't give me the rpm of the horsepower peak for the Cummins so I went with the 1800rpm you referenced. Doesn't matter though, rpm (and torque for that matter) is a component of horsepower. That's what the horsepower number is all about. It says hey, for performance, what matters is the total combination of torque and rpm. The makeup isn't important for performance because we can use gearing to convert it to whatever makeup we want at the rear wheels.

Now svpdiesel hit the nail on the head. For considerations other than performance, the rpm & torque makeup coming from the motor most certainly does matter.

"Did you actually say, or did I misunderstand you, that the Chevy will outpull the Cummins if it had the correct gearing?"

Absolutely. Assuming it has more power, geared correctly it's capable of putting more torque to the rear wheels for a given rear wheel speed. That's the very definition of horsepower, the combination of torque and rpm, and rpm is every bit as valuable as torque because it can be very easily converted to torque with gear reduction.

"That's what I have a problem with, it's just not gonna happen. Now maybe you can sit there and run all sorts of calculations @ rpm, gear ratio, wheel speed etc. And have it look good on paper, but the fact is, no chevy pickup, reguardless of gearing is going to outpull a semi, period. That's my only point."

Okay, you're sure it's not true. You can't explain, but you're sure anyway. That indicates an emotional attachment. Fine with me.

But this ain't rocket science. These are well understood facts. Anyone who's taken Physics 101 and understood the material can confirm it for you. Sayiing it ain't true doesn't change a thing. That was my point eariler, misunderstanding the laws of physics doesn't change them a bit. It's like arguing the world is flat. Doesn't change a thing.

"Obviously this is because although the semi has slightly less HP, it has a tremendous more amount of torque."

Your statement indicates that you don't understand the meaning of the word torque. Torque by itself is not a performance metric. Hell, I can make 100,000 ft/lbs of torque with a battery powered handheld electric drill motor, if I apply enough gear reduction. It'd be moving awfully damn slow though. Torque is only meaningful for performance when you consider the rpm it's made at; anyone can push hard if you don't have to push fast. When you consider the rpm AND the torque together, that number is called horsepower. Torque is not some independent entity that you add to the horsepower to get the total performance capabilty; torque is literally a component of horsepower, it's already built into the number. The other number that's built into horsepower is rpm, and it's every bit as important.

"We can't really sit here and argue that fact."

Especially if your argument is based in emotion. I assumed you were really interested in learning. It appears you've closed your mind.

"If the Chevy motor was capable of pulling better, obviously it would be in a semi for a savings of $10,000 or more."

See svpdiesel's response.

"My point was not to sit here and argue math and physics with you, any monkey with a formula and a calculator can do that."

Can you? That would be infinitely more productive than arguing an emotion-based position.

[ 02-20-2003: Message edited by: ZFMax ]

ZFMax

02-20-2003, 16:19

Great post TC. You got it, those engineers know this too, but they're designing for a whole bunch more parameters than just how fast it can pull a load up a hill. Operating costs and rebuild intervals have got to huge considerations in the design of an over-the-road truck.

FightinTXag

02-20-2003, 19:05

Guys it could be worse. It could be 8 years ago and ZF could be telling us that our 6.5TD's would be outpulled by 4.3L V6's. At least we're now measuring up to big blocks, plus we have 80-100% better mileage, early reviews seem to indicate the drivetrain will have excellent longevity, and that means our package will hold its value.

The 6.5L's in stock form will be outpulled by 4.3L V6's.
Think the 6.5L will get better mileage than the 4.3L?
Think the 6.5L will be more reliable than the 4.3L at 100k+?
Think the 6.5L will have better resale than the 4.3L?

Think again. I've owned both and the shortened 350 has the diesel beat in every category.

EWC

02-20-2003, 19:42

OK ZF , how about going over horsepower peak and ground speed again . The interesting point to remember was the 8.1 would beat a Duramax to the top of the hill . I'd like to see a test with 2 similarly equiped trucks , especially the rear axle ratios , and find out which engine is the best . I'd also like to see the Cummins run with the 8.1 . Why ? As you said , this is pure theory and you know what they say about theory , " believe the results and invent a new theory " . Theoretically I could take 100 weedeaters and strap them together and beat a Duramax . Not very practial . It's also interesting to note that you apply laws of physics but miss the point of torque , lbs per foot . You can't invert the words and come out with the same meaning . It does make a difference .

Burner

02-20-2003, 19:44

ZF,

Thank you for being good sprited about this issue. You have done well. ;)

I thought I might mention that "gassers" were used in "Big Rigs" after WW II. The truckers were trying to "get to the top of the hill" faster. They started dropping the big V's in. Well, It did not take long before the "gas motor" idea was in the can. The gassers demanded (by design) more RPM to reach the same torque and HP numbers. Although the trucks did pull harder and run faster they had problems. The motors were turning more RPM and eating clutches, gear boxes and FUEL. One of the really big problems occured when the trucks hit Ice patches. Do to the increased RPM, torque and HORSEPOWER the trucks were "snapping" drivelines. The "gassers" created HP & TQ so fast that when they hit Ice the tires spun too fast for recovery. I cannot imagine roasting that much mass, with that much weight and slamming it back on to dry pavement. :eek:

I guess every motor has it's place. If I really wanted to out pull and out run the CAT or 8.1 I'd get a really nice electric engine. ;) Like I said every engine/motor has it's place.

Burner smile.gif

afp

02-20-2003, 20:22

ZF,

You are 100% correct in your comments about HP vs torque. However, you are including some unnecessary emotion in your posts. You do not need to do this. You do not need to defend yourself this way. Your logic and info stand by themselves.

Blaine

FightinTXag

02-20-2003, 20:59

EWC,
Torque is measured in ft-lbs or lb-ft. That would be foot-pounds or pound-feet. It's the force applied TIMES the moment arm. It's not pounds PER foot which would be the force DIVIDED by the moment arm.

You guys that keep wanting to talk about the 4.10 ratio versus the 3.73 are missing the point. The point is that the higher rpm that the gas motor is capable of turning allows us to use the 4.10 rear end and/or a lower tranny gear for a greater mechanical advantage. Arguing for a comparison between like-geared rear ends is just like insisting the tranny be in the same gear. If you want max power from the 8.1, the allison will be in 4th or 3rd when the duramax is running in 5th or maybe 4th. That's where the horsepower of the gas motor comes from. It turns higher rpms so that the gear can be lower to get more leverage on the tires. The diesel will be turning fewer rpms so it's consuming less and its parts are subjected to less accelerating force and fewer fatigue cycles.

We, of all people, should be familiar with this concept if you stop and think about it. The 7.3L PSD's made close to the same torque numbers as the Duramax, but it could never come close it (stock for stock) in pull-offs or races because the Dmax made more horsepower by turning higher rpm. Thusly, we could hold a gear longer supplying more torque to the ground. It's greater horsepower came from the higher redline. I believe the last year for the 7.3L PSD, it made 525 ft-lbs. That's 5 ft-lbs more than the duramax, but it still didn't hold a candle to the dmax because of the horsepower and rpm differance.

Diesel Freak

02-21-2003, 02:23

Okay ZF, let's pull emotion out of this before it gets nasty. I appoligize right now for anything I said that offended you. I do not disagree with your calculations at all, and as I stated before, I understand how you are basing what you are saying. Where I'm coming from is this: and if you can explain it to me, I really would appreciate it. I am basing my opinion on a real world experience as follows: My 01 Dodge Cummins, turned up to 450hp (estimated flywheel, 400rwhp) it put 900 lb/ft to the ground, so I would guess it would be rated around 1000 at the crank. Can you tell me why, and I ask in all sincerity, that I could only gross out at 24,000lbs to maintain 65mph up a 6% grade, that was turning about 2500rpm in direct drive, which was right at the motor's hp peak. Any more weight, and I couldn't hold 65. The semi I was driving at the time had a 370hp Cummins in it. The exact same hill, @ 65 mph @1800rpm would handle a gross load of about 40 - 45,000lbs before it would start to lose speed. Both motors were running at their hp peak, and both vehicles were running 65mph, so I would think that the gearing was correct in both applications. Based on what you are saying, shouldn't my Dodge handle more weight?

I'm really not trying to be a smart@ss, because the scenario above is fact, I drove both rigs up the same hill numorous times with varying loads. This is where I am coming from. And I really am interested in seeing an explanation because from what you are telling me, my Dodge should beat the semi since it has 80 more hp, but it's just not that way for whatever reason.

ZFMax

02-21-2003, 02:33

Thank you FightinTXag, I read EWC's comments and was about to respond but you took the words right out of my mouth. As you pointed out so perfectly, comparing the a gas and a diesel with the same axle ratio would make the comparison invalid, not more valid, and to even make such a comment is indicative of a lack of understanding as to the differences in the motors.

EWC, on the ft/lbs thing, like I said that's what it says in my textbooks. I can give you the address of the publisher and you can argue it with them. It's a giant don't care for me.

Afp, not sure what sounded emotional fromme, but I can assure you, I couldn't be less emotional on this deal. Hey, I get insulted and it doesn't even phase me, I really don't care. If I came across that way, you can chalk it up to the distortions inherent in this medium. I'll be more careful though, thanks.

It sure is amazing to me how creative people can be arguing that these facts just *can't* be true. I'm not even remotely interested in making someone look or feel stupid, I just try to calmly lay out the truth and do it from various angles if that's what it takes. But a person has to open his mind to the notion that perhaps his long-held understanding could be wrong. Not everyone is willing to do that. Which is fine, it ain't my mission in life to educate folks who don't want to be educated. I don't think I'm going to succeed with DF.

[ 02-21-2003: Message edited by: ZFMax ]

Diesel Freak

02-21-2003, 09:22

Look ZF, I am being open minded, and I really do want you to explain why the Dodge wouldn't outpull the semi. I understand what you are saying about torque multiplication with gear reduction. I'm assuming that each vehicle has the optimum ratio for the given 65mph speed since both motors are running right @ their hp peak. I really would like this explained, like I said, looking at the numbers, the Dodge should outpull the semi, but for some reason it wouldn't. :D :D :D :D

FightinTXag

02-21-2003, 13:03

huntindog,
Ok, take my example on the first page. The 3.73 geared 8.1L would be turning 3500 rpm @ 61mph. Here it is making around 450 ft-lbs of torque.

450 ft-lbs
x1.41 3rd gear ratio
x3.73 rear end ratio
------
2370 ft-lbs to the rear wheels

This is still much higher than the 1940 ft-lbs that the duramax can put to the ground at the same speed.

FightinTXag

02-21-2003, 13:12

DieselFreak,
You're post doesn't make sense. You say you're Dodge makes 450 hp at 2500rpm. This means it would be making ~950 ft-lbs of torque. The semi makes 370 hp at 1800 rpm. This means it would be making ~1080 ft-lbs of torque.
Even if engine torqe mattered more than rear wheel torqe (which it doesn't) do you really think 130 ft-lbs of torque would let you pull 21000 more pounds up a 6% grade?? Think 14% more engine torqe should increase pulling capacity 88%?
Something is wrong in your numbers.

ZFMax

02-21-2003, 17:42

DF, I apologize, our posts crossed in cyberspace and I missed yours and I see that you do in fact have an open mind and are genuinely curious about that scenario.

Thing is, once again, Fightin took the words right out of my mouth. Something's not right about the numbers.

The only thing I can really guarantee you about any given scenario thrown at me, I mean without seeing the vehicles and measuring the power and weight and gearing myself, is that both vehicles will obey the laws of physics. The results will follow them exactly. And the laws of physics say that if the wheels are going the same speed, the wheels with the most horsepower also have the most torque at them. That's not something that's even in question. I'm highly skeptical when anyone describes a situation that violates the laws of physics. The data has to be wrong.

afp

02-21-2003, 19:25

ZF,

You and I approach this stuff the same way. I like what you post and how you post. Like you said, this is a distorted medium when it comes to accurately conveying info. Things that we can say in person and get laughs are often perceived as offensive in Internet forums.

I almost hate to explain myself further, but I am afraid I'll leave you with the wrong impression if I don't. Also, I really don't weant to sound judgemental here, as I struggle with the same stuff myself. I find whenever I use one of these "mildly" emotional statements, I am "zinging" someone and have to admit I'm just trying to show how clever I am. Maybe I am totally off base and just reading my own usual motivations into your comments. Anyway, here are a couple things you have said on this thread.

"To deny it is just silly and ignorant."

"If not, and you prefer to live in denial, that's cool too, I'm not concerned"

"Okay, you're sure it's not true. You can't explain, but you're sure anyway. That indicates an emotional attachment. Fine with me."

In the above staements, you have called whoever you were responding to "silly and ignorant," "living in denial," and "emotional" (emotional in a negative way). None of those comments really add anything to the excellent information you present and the sound logic you apply.

Sorry for sounding like "Mr Posting manners." I am fairly certain you don't mean those comments as I am taking them, so apply the appropriate "grains of salt" to this post.

Now I do have a real question on the meat of the topic. Why is it that when it comes to converters holding up, we worry about torque output instead of HP?

Blaine

Diesel Freak

02-21-2003, 20:39

ZF, looking at the numbers, I would agree that the wheels with more hp, should have more torque. I'll tell ya as much as I can. The Dodge was dyno'd on a chassis dyno @ 400rwhp, that I'm sure of, I'm pretty sure the hp peak was right around 25-2600. The torque came out to about 900, @ I believe 16-1700rpm. I'm estimating, and tell me if I'm wrong, that should be about 450/1000 at the flywheel. The only thing I know about the Cummins is it is rated @ 370 hp and 1450tq @1200rpm. I don't know what the rpm for the hp peak is, but the motor was "low rpm" motor (governed at about 1900rpm) 1800rpm seemed to be the "sweet spot" it pulled best at. Which was 65mph in 9th gear (direct drive 1:1) The Dodge pulled best @ 2500 or so, which was 65mph in direct.

I'm really scratching my head on this one, because it doesn't make sense. If I was loaded over 25k with the Dodge, I couldn't hold 65mph. The semi weighed 32,000 empty, and it would fly over the hills @ it's governed 72mph speed. When I grossed much over 40k, I couldn't hold 65 and would have to drop another gear or two. Is there some other factor we are forgetting? The Dodge had a 3.55 rear end, I couldn't tell ya on the semi, I would guess around 3.11.

Thanks!!

EWC

02-22-2003, 10:44

FightinTXag , thanks for correcting me . You are correct that torque is measured in lbs-ft . As you have stated ; torque is measured as force multiplied by a moment arm . In this example force ( lbs ) times a moment arm ( ft ) = torque . Another way to look at this , take a 3 ft breaker bar and apply 200 lbs force to the end of the bar , at a 90 degree angle to the end of the bar , and you have a measured torque of 600 lbs-ft at the center of lets say a 1 inch socket . Now turn this around and apply a 3 ft breaker bar to 200 lbs of force and you get .. ah .. you get .. help me here . What do you get ? Yes the math says that you can flip the numbers around and still get the same answer , but does it make any sense ? MPH , RPM and other abbreviations are easy to figure out , what about torque ? Most of the people use the incorrect terminology , even Snap On with their torque wrenches , except 2 people that I know of . One was a college professor that first said something about ft-lbs being a misnomer ( my response was you're crazy and everybody says it anyway ) and the other more current person is Warren Johnson of NHRA Pro Stock fame . In the October 18 2002 issue of the National Dragster , under Speed Reading , he refers to the Chevy engines and torque rating in pounds-feet of torque . This is not the first time he has used the correct terminology and it will not be the last . Remember , you will need an open mind to talk about torque and may have to dispose of some common misconceptions . The world is still flat because it was printed in all the books and was believed by all to be common knowledge , right ? Now on to the running of the trucks with the same rears , the purpose of running the same rears is to eliminate any variables so that the only comparison is the engines . If you want to run them with the 4.10 rears , run them both . Then run them with sticks . The point is to only change one thing at a time so that you can come to a valid conclusion , not that I don't understand the difference between a gas and a diesl engine . I'd also like to know when you dismiss torque and look harder at HP . Remember you said the HP is what matters but in the formula you need torque and RPM to get HP . If the torque is constant and you increase RPM you get more HP . What if the torque falls off ? You now need more RPM . It seems to me that HP is more dependant on torque than the other way around . Someone else posted that torque is a twisting force and HP is how fast you accelerate work . What happens if you have no acceleration ? The torque is still there but no increase in HP . Now what ? Others have posted about results from the hill climb , Tough Guy for one . Now we have a yardstick to shoot at , Bill Heath's Dodge and some numbers . These are results not heresay . What facts can you supply to back up you claims ? And you still have not answered the last question about the Cummins .

Lower_Suburbia

02-22-2003, 11:30

I love these discussions. There has to be something we are leaving out of the equation.

I know in the real world from driving big rigs that as your rpm drops towards your peak torque rpm a truck will pull harder. I

pinehill

02-22-2003, 11:39

From a dimensional analysis standpoint, ft-lb is every bit as correct as lb-ft. The problem lies in the English system of measurement (as opposed to the metric system). Unfortunately, in the English system, pounds can mean either force or mass. In the metric system, we have slugs for mass and newtons for force.

So, in the English system, we distinguish between a measure of potential energy (a mass which can drop a certain distance) by using ft-lb, and torque (a force applied to a certain lever arm) by using lb-ft.

This is really just scientific esoterica, and anyone who uses (or misuses) either term is still OK in my book. ;)

Diesel Freak

02-22-2003, 20:40

Lower Suburbia: I agree! It does feel like the truck pulls harder at the lower rpm. And actually according to the equation, it does have more torque. My 370hp motor is only putting out like 900 tq @ 1800, but 1450tq @ 1250. That's something that kind of confuses me. So would you say that the torque peak rpm would be the best rpm for towing and not the hp peak? Is that the part we are missing that explains why the semi will outpull the pickup? Not being a smart a$$, I really am wondering???

afp

02-22-2003, 22:08

We need to know the final drive ratio where the semi makes peak power. The we need to know the final drive ratio where the pick-up makes peak power.

FightinTXag

02-23-2003, 19:35

EWC, you're playing games. You say 200lbs applied to a 3 ft breaker bar makes sense. Apply a 3 ft breaker bar to 200 lbs? How about a 3 ft breaker bar with 200 lbs applied? That makes sense. 200 lbs with 3 ft breaker bar applied? No. This is semantics and it's pointless. You're filling in words to try to determine the order of primary units when defining secondary units. How does that work in other languages where the nouns, verbs, and adjectives are often in different order. A Newton is a kg-m/s^2 (kilogram-meter per second squared). It doesn't matter if you say m-kg/s^2 (meter-kilogram per second squared). It's the same thing. Bottom line is you can say ft-lbs or lb-ft and it means the same thing. I'm not going to argue about this anymore.

EWC, If the rear ends must be the same between trucks for any comparison to be valid, then I guess the diesel pull-off was a waste of everyone's time. The point of my original post using the 8.1/A/4.11 gearing was to respond to the topic starter's question about how his D/A could be outpulled by an 8.1/A. If all a truck buyer cares about is getting a load up the hill as fast as possible, which is what we were talking about, the 8.1/4.11 is a better choice than the Duramax. Besides, this is a moot point since an 8.1/A/3.73 still gets more torque to the ground than the D/A. This is another dead horse as far as I'm concerned.

EWC, If torque falls off the table as rpm increases then, all that means is the horsepower peak may be lower in the powerband. Horsepower is a combination of torque and rpm. Where that combination is maximized is where the potential to do work the fastest is. That's what horsepower is, a measure of how fast work can be done. If an engine's torque falls dramatically at rpm above the torque peak, then the horsepower peak may be close to the torque peak. Maybe that's why DieselFreak and LowerSub think their semis pull harder at low rpm. That may be where the horsepower peak is. Nobody claims their Duramax pulls hardest at 1800rpm. If that were the case the allison would never downshift.

EWC, Every one of my posts is fact. They're not "claims." I responded to the post about the Diesel Freak's Cummins. The numbers don't make sense. See above.

HUNTINDOG, I see what you're saying, but I believe the Duramax would upshift before the 8.1. I owned an '01 8.1/A and it was much easier to get to downshift than the dmax. The dmax would be more likely to upshift and then downshift again at the next hill. If the 8.1 upshift, it would surely downshift at the next hill and be supplying more torqe to the rear wheels again.

AFP, because torque converters are in line between the engine's output shaft and the transmission's planetary gears, the engine's max torque output is the most torque it will see. The driveshaft and U-joints are after transmission's gears so it could be subjected to the engine's torque times the first (or reverse if it's higher) gear ratio (also factor the transfer case's LO ratio). Wheels and axles could be subjected to the max torque the driveshaft and U-joints see times the differential ratio.

PINEHILL, slugs are actually an English unit. That's what's confusing about English units. It's set up to where a pound of mass will weigh one pound of force on Earth. A slug will actually weigh 32.2 pounds of force on Earth. A pound of force then is actually defined as 32.2lbm-ft/s^2. Since there are 32.2 mass pounds in a slug, you can also say a pound of force is 1 slug-ft/s^2.
The metric system uses grams or kilograms to measure mass and Newtons to measure force. One Newton is 1 kg-m/s^2. However, one kg will actually weigh 9.8 N. Much less confusing. ;)

FightinTXag

02-23-2003, 20:28

Nope, it was a 4.11.

pinehill

02-23-2003, 20:47

FightinTXag,

I agree; you're correct on the slug. It's been so long since I took college physics that my memory must be getting slug-ish. smile.gif

Paintdude

02-23-2003, 20:49

I have always seen the dyno numbers taken at the engine are higher than at the rear wheels..Our Motorcycles make 106hp at the crank stock and 97hp at the rear wheel stock..Just what I have experianced..Loss of hp through the mechanics to put it to the ground..

Plus it is the compresion of the diesel that makes the difference..twice a ratio of the 8.1..

we measure the torque while riding our motorcycles in top gear roll-ons with same gearing..The bike with the most torque always pulls ahead even if it does not make the most HP, but when the higher HP engine gets to its power band, it will tend to shorten the gap..

It took me alot of years to figure it out, but deisel is definatly the way to go..

VaDmax2003

02-23-2003, 21:16

I pulled a 32 ft TT (approx 8,000lb.)with my 96 Suburban, 2500, 454 vortec, and 4.10 rear end. I had about 20,000 towing miles on that combo, including a 12,000 mile Alaska trip in 2000. I could always maintain decent speed (45-60 mph) on most interstate mountains but it really struggled on a west bound Alaskan Highway pass between Ft. Nelson and Watson Lake and I topped it at about 20 mph while holding my breath. I have only pulled that trailer with my 2003 Duramax about 30 miles on the local flat terrain and it will be summer before I really get to test its mountain pulling performance. However, I can say that its level terrain performance such as accelerating from a stop light or accelerating to pass and other vehicle is outstanding and is no comparison the suburban, and, I need to keep remember I am towing something. The transmission braking in tow/haul is also out standing. I towed a UHaul car carrier loaded with a Nissan 2dr car back from Chattanooga. On I-81 from near Knoxville to Staunton, Va., and, on eastbound I-64 over Afton Mountain it ran at 65 mph easily in overdrive. In Chattanooga on the hilly local streets, after touching the brakes on a rather steep down grade, I did not use the brakes again till I brought it to stop at a traffic signal. I cannot wait to get it on the road this summer for some serious trailer pulling.

RATDOC

02-23-2003, 21:39

NOT to add fuel to the fire, BUT.........
there's 2 things everyone is overlooking:
1) the POWER CURVES of each engine.
2) the simple fact that these engines are both COMPUTER CONTROLLED.

An engine with more power can easilly be beaten by one with less IF the lesser of the two has a better power curve and offers a more constant pull rather than one that offers a burst of speed and then falls off.......slow and steady gets the job done. This of course will apply only to those that have been optimized with the proper gear ratios, shift points, etc..... Plus we all have to remember that both of these engines are NOT set up for their full potential in a pull-off. Being that they're both controlled (and limited) by the factory computer programs, neither one was properly optimized for pulling but rather a combination of everyday driving, fuel ecconomy, towing, proper emissions, longevity, etc.....
Comparisons can only be made in a proper fashion IF ALL the cards were on the table. While I'm NOT siding with either engine, we must all realize that each has a plus side as well as a minus side and certain laws of physics that DO apply DO NOT neccessarilly prove one as 100% better than the other.
Tom

orange2

02-23-2003, 22:06

Here is how it was explained to me. torque is the amount of work an engine can do, hp is how fast it can do the work. lets talk farm tractor, cause its all I know. A 300 hp tractor with 1200 tq will pull a 30 ft implement 6mph but a 425hp tractor with 1400 tq can pull it 8mph. My Dads semi has 1200 tq and mine has 1250, his has 350 hp mine has 450hp, with 80000 pounds going up a hill we both hit the hill at about 45 mph, at the top of the hill he is down to about 35, mine is only down to 40mph, that is what hp does for you. He can do the same work or move the same load, just not as fast.

ZFMax

02-24-2003, 09:31

In any given gear, of course a vehicle is going to pull hardest at it's torque peak, not it's hp peak. However, keep in mind it's going slower at it's torque peak, which makes it an invalid comparison. The way the comparison should be done is at it's torque peak versus a gear lower and at it's hp peak going the same speed. When you do it that way, you quickly see that the truck pulls hardest for a given ground speed at it's hp peak. Which is obvious when you look at the formula. Hp is torque x rpm, or in other words at the same rear wheel rpm, the rear wheels with the most hp have the most torque.

If you don't believe that then by all means, don't bother downshifting when you come to a hill. Just stay in the right lane, because people who understand that they get more torque to the rear wheels (where it matters) at a given speed at their hp peak are going to be moving around you.

Orang2, I like your post, I mean technically torque is not work and you can have a million ft/lbs of torque that can do nothing if you have zero rpm, but you've got the basic idea other than that and I'm just nitpicking over the terminology you chose.

Look at it this way instead. Torque is just twisting force, without regard for whether you're applying that force at 1rpm or 10,000rpm. If you need more torque because you got a big load pointed up a hill, you downshift. That lowers the rear wheel rpm but raises the rear wheel torque. Even a handheld electric drill motor can move that 80,000lbs up the hill, it's just a matter of gearing it deep enough and how long you're willing to wait.

Ultimately, how fast you're going to get the work done is therefore a function of both how much twisting force the motor is making and how fast it's spinning as it's doing it. In other words, the COMBINATION of torque and rpm. That number is called horsepower.

Contrary to popular belief, torque is not more important than rpm when determining how fast work can get done. In fact, the two are completely interchangeable. Gear something down by 2:1, and you double it's torque and halve it's rpm. Gear it up by 1:2 and you halve it's torque and double it's rpm. Ultimately, it's the total combination that matters for performance, and that's called horsepower.

afp, the engine's peak power point is not a function of it's gearing.

Paintdude, the type of dyno you're referring to actually shows engine torque as measured at the rear wheel, not rear wheel torque, and there's a HUGE difference. Rear wheel torque will vary radically depending on the gearing of the bike and what gear you do the pull in. A Dynojet won't even attempt to show torque unless you use the tach pickup so it can calculate how much gear reduction there is between the engine and the drum. Notice how when it shows torque, it plots it against engine rpm, not rear wheel rpm. It's engine torque. The Dynojet's results will vary slightly from one gear to the next largely due to the variation in frictional losses through the gearbox for various paths.

The hp is actually the same at the crank versus the rear wheel and all points in between. It consists of different combinations of torque and rpm at various points but the it's all the same horsepower. Sure, the drivetrain causes losses, but the crankshaft sees those losses too so long as it's hooked up. The only way you'd get higher hp readings at the crank is if you test it there with the drivetrain disconnected and removed those losses.

RATDOC, the scenario described was at two fixed rpm points. The curves don't matter when you're talking about that.

RATDOC

02-24-2003, 10:07

ZFMAX- while I totally understand about your comparison being at a fixed r.p.m., the main point of my post was to elaborate a little further and show how we're ALL going off the beaten path from the original topic. At specific r.p.m.'s, one engine would beat the other, and at a different r.p.m. the other might win........we should try to make a more general comparison instead of dwelling on varios laws of physics which don't always prove something as being "generally" better. While I agree that specific passenger and light truck engines CAN make better pulling power than one found in a big rig......it's the GENERAL and OVERALL results that count. Quite possibly the reason that companies like Cummins, Detroit, and Catapillar exist and why we don't see too many big rigs with stout big blocks in them.
We need to make a comparison in a more general matter based upon each engine's strong points.....
I personally DON'T drive at a specific r.p.m., nor does anyone I know.
Like I originally stated, EACH engine has its strong points as well as some weak ones......it's up to each of us as "educated consumers" to choose the one that best fits our needs prior to putting down the $40K. :rolleyes: :rolleyes:
Tom

afp

02-24-2003, 16:01

ZF,

Yes, but we need to know the respective power peaks to determine the optimum final drive ratio for each engine. That way we can gear each rig accordingly, then test them to see which gets to the top of the hill first with the same GVW.

Also, why are we concerned with peak torque instead of peak HP when deciding how much a torque converter can handle?

Blaine

ZFMax

02-24-2003, 23:00

Well, torque is twisting force, and horsepower is torque times rpm. Clutches & converters are rated for maximum torque instead of hp because they have to withstand that twisting force but they're not sensitive to the speed they're going when they do.

Look someday at how a Harley engine is put together versus say a Japanese sportbike. The Harley is a long stroke, low revving, relatively high torque engine. It uses massive flywheels and crank pin and connecting rods and sprocket shaft and all that stuff because those things have to carry the torque.

Now look for example at a R6 motor. Small, lightweight stuff. It doesn't have to be big because the motor makes very little torque. The R6 winds to the moon (15K rpm!) to make it's hp instead. And it'll flat kick the snot out of any Harley ever made. Why? Because it uses gear reduction to turn that low torque at the engine into high torque at the rear wheel. Even though it's torque is lower, it's total combination of torque and rpm are greater than the Harley's.

FightinTXag

02-25-2003, 21:38

RatDoc, the comparison wasn't at a fixed rpm. It was at a fixed speed which gives us two rpm cases for the two engines. Most people pull near the speed we were discussing. Also, ZFMax did a good job of estimating the difference in curves for the two engines on page 2 of this topic. Everything else you say about engine comparisons is dead on. We've been saying all along that there are other considerations aside from how fast we can get a load up the hill. That's just the subject of this topic.

AFP, I was trying to explain about the converter thing earlier, but I guess I should've started by saying that forces and moments are what breaks things, or in this case may cause slipping. The torque that an engine puts on converters is more of a concern than the forces associated with their rotating speed. If the converters were at each wheel, however, we would be concerned about horsepower because they would be subjected to rear wheel torque instead of engine torque. This is what I was trying to convey in my response to you.

Huntindog, I don't understand the apples, oranges, and grapes comment. If getting the vehicle up the hill the fastest is what we're worried about, then if and when the hill flattens slightly, we won't be letting up on the pedal. Therefore, the only reason the 8.1 would upshift is if we have reached the top of the rpm range. If we have gone up in rpms then we must have increased speed. If we have increased speed, then we have increased momentum, not decreased.

Huntindog, I think instead what you're trying to say is that we will have an instant of no torque to the rear wheels during a shift. Finding a hill that kept the 8.1/A combo constantly upshifting and downshifting to where the time spent shifting was significant enough to offset the horsepower difference would be difficult. At least, I think it would be since constantly shifting is detrimental to transmission life and the Allison is computer-controlled to limit that type of behavior. I would think that any busy shifting would be more of a hindrance for the D/A since the power will drop off right before, during, and right after a shift as the Dmax defuels to protect the transmission. I don't think the 8.1 does any computer governing of the engine except on takeoff.

afp

02-25-2003, 22:30

ZF and Fightin,

Makes sense. If I apply 100 ft lbs of torque to a bolt rated at 75 ft lbs, it will break regardless of how fast I move the wrench.

All we need to do now is put an 8.1 in a semi, gear it approproately, and see how fast it gets 80,000 lbs GVW to the top of a hill.

Blaine

Mic

02-26-2003, 18:23

What if we were to govern each engine at 3000 rpm. Then which one would get there the fastest?

;)

FightinTXag

02-27-2003, 01:06

Mic, if we governed each engine at 3000rpms, then the 8100 would be dead in the water since it's only making about 250 horsepower at that rpm. I don't know why anyone would do that though.

Huntindog,
[That's news to me.
Are you saying that the engineers for GM didn't think it was necessary to protect the Allison from the "more powerful" 8.1???]

That's exactly what I'm saying if you read some of the above posts you'll see that engine torque is what will break a transmission. The duramax has more of it than the 8.1L.

[On both of these hills the grade flattens out to the point that you actually (depending on load) have to back out of the throttle to keep from gaining too much speed. ]

On the way up the first part of the hill the 8100 should be able to pull faster and reach the flat spot sooner. Since the trucks have similar handling characteristics, they should be able to take the curves at the same speed. The 8100 should pull the second part of the hill faster again.

FightinTXag

02-27-2003, 04:49

Yeah, you're right Huntindog. All engineers live in fairy-land and we have nothing to work with, but heresay formulas and dreamland theories. That's why nobody can ever predict the way anything is going to behave or perform. I tell ya what. It's 4:30 in the morning and I'm here at a refinery that is starting up after the revamp of a unit. I'm taking measurements and inspecting construction to make sure that my dreamland theories perform the way their supposed to in reality because if they don't at the very least, millions of dollars will have been wasted, and at the worst lives will be lost. Later on when I'm standing on top of a 250' tall vessel making sure things are happening the way my calculator says they will, I'll have a little chuckle about your "armchair engineer" comment. ;)

Tough Guy

02-27-2003, 10:06

Acceleration (sec) 8.1L 6.6L
Solo 0-60 9.0 9.5
Towing 0-60 30.3 24.4
Towing 40-60 16.4 13.0

I have asked why the 8.1 with more power is SLOWER than the Dmax loaded 3 times now....

All anyone wants to talk about is calculations of TQ/HP.......

http://www.trailerlife.com/test/0010v8.cfm

Scroll down to where it says "ACCELERATION"

**Note the Dmax is 1000lbs heavier, and while towing the Dmax beats the 8.1 in 0-60 and 40-60......With less HP how in the world does it do this? Now imagine if the test would have included 0-60 and 40-60 on a 6% grade........

Its NOT just about HP.

Cheers

ZFMax

02-27-2003, 18:04

Which is geared shorter relative to the engine's power peak, a 3000rpm motor with a 3.73 axle, or a 4200rpm motor with a 4.10 axle?

Did you not see all the references to gearing in the above explanations?

Are you aware what effect shorter relative gearing has on acceleration?

If I showed you an example of a 100rwhp, 40ft/lb motorcycle (Yamaha R6) stomping a 70rwhp, 80ft/lb motorcycle (Harley), would that prove the opposite point?

Sigh. This is silly. You describe basic, well understood physics from 14 different angles, and people still find a way to cling to what they want to believe. It's like a religion or something.

I guess I can see how no one wants to be told that they didn't understand what they were buying when they shelled out an extra $5K for a high torque motor. Whatever, it ain't my mission in life to convince you, I really don't have any interest in this anymore. Rest assured though that I bought mine full well knowing what the word "torque" does and doesn't mean, and I bought it anyway. It has advantages. Performance just doesn't happen to be one of them.

Tough Guy

02-27-2003, 18:32

I offered a simple fact, one very relevant to the first post in this topic thread....

Loaded with 10,000lbs the Duramax will outperform the 8.1 and with 40HP less, why?

Quoting ZFMAX:
"The notion that many people seem to have that somehow horsepower made of high torque and low rpm (i.e. a diesel) is stronger than horsepower made of low torque and high rpm (i.e. a gasser) is pure nonsense. The high torque/low rpm diesel motor has certain advantages, but performance over a gasser of the same horsepower is not one of them"

Better 0-60 and 40-60 times would indicate to me that the "performance" of the Duramax is superior to the 8.1......

The gearing difference you describe in your above post would only give the Duramax a bigger advantage.

Cheers

afp

02-27-2003, 21:01

Here is the acceleration results from trailer life. One thing that strikes me is the towing tests were accomplished a 2000 altitude. At higher altitudes, the DMax's waste-gated turbo will lose less performance than the naturally aspirated 8.1. Most likelt the DMax can maintain full boost against the wastegate at 2000 feet altitude and thus maintain very close to it's rated power output, while the 8.1 will lose a significat amount of power. When I drag raced, I remember that a 10 sec naturally aspirated car's index was adjusted by about 1/2 sec at 3000', and the slower vehicles were adjusted even more. These were cars optimized for acceleration. It's easy to see how 16 sec class truck could lose even more.

What this does show is another advantage the DMax has over the 8.1 when towing--the turbo allows the Dmax to maintain it's power much better at altitude. Now, if we turboed the 8.1, there would be no contest interms of raw power and acceleration.

***************************
Acceleration
There were no major surprises during the acceleration tests, in that the figures were as we'd expect for these engine-and- load combinations. The solo 0- to 60 mph runs were done at sea level, and the towing tests were performed at approximately 2,000 feet elevation. It's probable that acceleration runs at sea level would have cut a minimal amount of time from these results.

Acceleration (sec) 8.1L 6.6L
Solo 0-60 9.0 9.5
Towing 0-60 30.3 24.4
Towing 40-60 16.4 13.0
*********************************

Blaine

Tough Guy

02-27-2003, 21:23

Another fact you left out Blaine was that in that test the Duramax was 1000lbs heavier...

I think that would more than make up for the altitude...

Loaded the Duramax is just plain quicker than the 8.1...

Cheers

FightinTXag

02-28-2003, 01:30

Toughguy, scroll down to where it compares the two pulling. The 8100 pulled the hill 10mph faster than the dmax with full throttle applied for each truck.
They ran them on a twisty hill and found both could only run 40mph because they have similar handling.
The last hill has the 8100 pulling the hill 8mph faster than the dmax.

It doesn't make sense to me for the 8100 to pull a hill faster than the D/A, but not out-accelerate the D/A on flat land.

I don't know much about the turbo systems on the Duramax. Maybe AFP is onto something.

Huntindog, sorry that in your work, as a food clerk according to your profile, you have experience that leads you to believe engineers are not held accountable for real world results. I advise you to not make that assumption for engineers in general because most of the time, it flat out ain't true.

[ 02-28-2003: Message edited by: FightinTXag ]

Colorado Kid

02-28-2003, 10:50

When is the next pull-off?

Until I've seen what an 8.1 can do with a load I've pulled up the same hill I'm refraining from further comment. I have my hunches, but that's all they are. I will not be betting any 8.1 owners that I can climb it faster than they can.

Last year I offered a PSD (7.3) owner dinner if he beat me up the hill, but he didn't come out to play (and he lives in western Montana!). I'll admit that I expect a stock G2 to beat my time this year, and I'm hoping a Hemi will show up as well. It will be depressing if a Hemi beats everything else up the hill, it would have the highest rated power...but it's going to spend some time in first gear getting it wound up to where the power is...the standing start test works against it. Like I said, I hope one of everything shows up, and we'll see how they do.

Tough Guy

02-28-2003, 13:33

FightnTXag-
I did read the article, compare the RPM of each truck relative to each trucks peak HP...the Duramax ran all the hill 2200-2400 and 8.1 was at 4200...

Colorado kid-
The pull-off will be in June...

My point is, if the 8.1 can't outperform the Duramax on flat ground it certainly will not on a 6% grade pulling 10,000lbs.

Lone Eagle

02-28-2003, 20:24

Sounds like the Dmax was in the wrong gear. Later! Lone Eagle ;)

ZFMax

03-01-2003, 19:38

"The gearing difference you describe in your above post would only give the Duramax a bigger advantage."

Wow, guess my explanation blew right by you. The point I was making, that you apparently missed, is that the Duramax IS geared deeper than the 8.1, when you consider the engine rpm where they make power. Motors that make their power with higher rpm and lower torque need deeper gearing, we've gone over that ad nauseum. The 8.1 has it's power peak at a 40% higher rpm, but it's only geared 10% shorter. Which explains those results perfectly. To accurately compare the acceleration capability, the 8.1 would need a 4.90 rear gear.

We haven't really gone over the effect of gearing on acceleration, but just conceptually, if you understand the meanings of the words torque, rpm, and horsepower, and the role played by gearing, I'm sure you can visualize how it can have a dramatic effect. I'm not really up for going through the physics of it to be honest with you, and I doubt you'd believe me anyway.

CPMac632

03-01-2003, 20:17

I didn't know the 4.90 ratio was an option on a duramax or a 8.1.

Tough Guy

03-01-2003, 22:21

ZFMAX-

I think my point(s) are blowing right past you....

I will ask one last time:

Why if the 8.1 makes more power than the Duramax as you have descibed, calculated and posted over and over again is it SLOWER than the Duramax 0-60 and 40-60 with 10,000lbs in tow?????

Just give me the answer, not if I told you this or you won't listen, blah, blah....

Just the answer......

Here's an example: Well guys, because of the Duramax TQ/HP curve, the drivetrain is able to transfer the more power to the rear wheels at any given RPM, therefore moving the truck and trailer faster from a stopped position.....Although, at highway speeds the 8.1 is more able to utilize the top end of the RPM range where peak HP is attained thus increasing its performance over the Duramax......

Cheers

afp

03-01-2003, 22:39

Tough Guy,

ZF's point was clear to me. The 8.1 did not have optimal gearing for the test. The Dmax was geared much closer to it's optimum gearing. To have a valid test, both trucks need to be geared optimally.

Blaine

CPMac632

03-02-2003, 08:50

I get his point but think it is irrelevant. The reason a duramax pulls a load better is with the gear ratio and rpm it makes power at, coupled with its long flat torque curves, in other words it puts down more across a wider range of mph in each gear. Sure if the 8.1 had a 4.9 gear it would have more to the ground but it still wouldn't have the broad range of power in each gear so it would probably still get there last with a load.

ZFMax

03-02-2003, 09:05

TG: what afp said. And I'll add that I'm sorry that I apparently can't put this in simple enough terms for you. I've done the best I can. I get the distinct impression that you're resisting the information instead of genuinely trying to understand it.

CPMac: that's not true. Read this entire thread, we went over that point in detail. The 8.1 has a significantly broader powerband.

CPMac632

03-02-2003, 09:09

So your saying the 8.1 already has more to the ground at any given speed but can't pull a load better. Yeah right. And why do you want to gear it differnt with a gear ratio that isn't even available. Put a supercharger on it then it will easily outpull a dmax.

Tough Guy

03-02-2003, 09:18

ZFMAX-

You still did NOT answer my question....

If the 8.1 makes more power, than why is it SLOWER than the Duramax on the loaded 0-60 and 40-60??

Remember, 340hp is more than 300hp......

Is it that hard to admit you are wrong???

Cheers

Tough Guy

03-02-2003, 09:30

AFP-

Now you are making excuses too?

I think you should also re-read this thread, from what I read I thought that the 8.1 made more power all the time, had a wider power band...etc...

It can't perform as "theory" suggests, so now we are at a gearing debate...please, just admit you are wrong.

The Duramax is faster with a load than the 8.1 reguardless of HP.

This not an opinion, this is fact.

Cheers

CPMac632

03-02-2003, 09:36

Ok I went back and read every one again and your misrepresenting physics scriptures still doesn't convince me.

[ 03-02-2003: Message edited by: CPMac632 ]

afp

03-02-2003, 12:06

Reread this thread? I have better things to do that enagage anyone in a pi$$ing contest, and that is exactly what is starting to happen here. I'm out of this thread.

Blaine

[ 03-02-2003: Message edited by: afp ]

JoeyD

03-02-2003, 14:54

WOW. This is long reading...

Tough Guy, It looks like the next pull off needs a 8.1 HD with 4.10 gears for a comparision. Do you have any pull with the owner of the site to make it happen?

Diesel Freak

03-02-2003, 15:25

I never did get my question answered about the semi vs. pickup either. I can take this a little further and ask why my 320hp V-10 Dodge, my 320hp Denali, and my buddy's 345hp Hemi Dodge won't outpull my Duramax. There has GOT to be something we are all missing, I wish I knew what it was. Sure doing the calculations applying the laws of physics, the 8.1 at a specific RPM with a specific gear ratio is putting more hp to the ground, I'm not arguing that point. What I am arguing is that my "lesser HP" semi will drastically outpull my pickup with more HP. Both vehicles apparently have the correct gearing, because both engines are running right at their HP peak, which has been explained is where they put the most power to the ground. So WHY will the semi out pull the pickup??? I know I'm not the only one here who has driven truck, and I feel quite certain that those of us with cranked up D-Max's will never put them up against a semi and expect to win. What are we missing in the calculations??

CPMac632

03-02-2003, 16:28

Anyone know where to find a dyno chart for the 8.1 at?

EWC

03-02-2003, 16:37

OK Fightin and ZF , I have scheduled a 3 way conference call with you and Chevrolet so that you may explain to them that all the literature on their website , that has listed torque as ft-lbs , is incorrect and needs to be corrected immediately . Everywhere that I looked , torque was listed as lbs-ft . What do you guys know that Chevrolet does not ? Will you share your knowledge with us, please ? You keep saying that the 8.1 puts more power to the ground , but that is not true . If you do the calculations that Fightin did , on the second page , and go all the way to the overdrive gear , you will see that the only one that makes more power is the 8.1/ZF/4.10 combination , 1377 lbs verses 1417 lbs . This includes the 8.1/Allison/3.73 and 4.10 combinations . You compare the Duramax to the 8.1 @ 60 MPH and see that the Duramax runs @ 1800 and the 8.1 runs @ almost 4000 Rpm in 3rd gear . Who the heck runs 60 MPH in 3rd gear ? Apparently you do . What about the article that TG brought up ? You claim that the 8.1 isn't geared correctly , but dismiss the fact that the Duramax is carrying almost a 1000 lbs more as irrelevant ? You are missing the fact that the Duramax has a flat torque curve from 1800 RPM to almost 3000 RPM and that is what moves the load . The 8.1 has a narrow peak and doesn't make as much torque . You keep bringing up 340 HP @ 4200 RPM . How do you propose to run the 8.1 at the pull off ? Bring it up to 4200 and pop the clutch ? It's funny that you keep saying that because of the higher usable RPM the 8.1 can run a taller gear . I always thought if you had a weaker engine more gear would tend to help it . No TG is right , admit that the Duramax is the winner in this one . It will go easier on you in the future . smile.gif

EWC

03-02-2003, 16:43

I found the HP and torque on the GM powertrian web site . Diesel Freak , mind if I take a crack at it ? What exactly is your truck , trans , rears , etc .

CPMac632

03-02-2003, 17:27

ZFmax where in my figures am I going wrong. The 8.1 will pull to around 4300 then shift and drop to around 2700, the Max will pull to 3100 then drop to 2100, both of these should be loaded situations. The 8.1 is around 425 tq from 2500 to 4300 and the max is 500 from 1500 to 3000. Using the equation with the 8.1 geared 4.10 and the max 3.73, the minimum rwtq across each gear is always higher on the Duramax. In fact I can't find one example of the 8.1 having more rwtq than the duramax in any given gear.

[ 03-02-2003: Message edited by: CPMac632 ]

Diesel Freak

03-03-2003, 00:05

EWC, be my guest, my question is on the previous page, Dodge with 450hp, 3.55 rear, in 5th gear (direct) vs. Semi with 370hp, 3.11 rear (I'm assuming I'm pretty close considering rpm and extra height of tire) 9th gear (direct) Both motors at their respective hp peak (or dang close) both vehicles @65mph, Dodge with ~22k Semi with ~40k. Why won't the Dodge pull more weight than the semi since it has quite abit more HP? Now I realize I might be off a little on the semi's rear end, and maybe off just a tad from absolute peak hp with the RPM's, but you can't tell me that I'm so far off as to make damn near double the difference. The Semi is moving practically twice the weight of the pickup which has substantially more HP. WHY????

RATDOC

03-03-2003, 07:16

The bottom line here is like I said earlier....... every engine has a sweet spot and in some instances can LOOK better than another one in certain senarios and that's how he made the claim about the semi engine being beat by the pick-up engine. HOWEVER, it's the OVERALL results that need to be looked at...........Like I said earlier, IF these engines were so good at putting all this power down, WHY DO THE BIG RIGS EVEN BOTHER TO USE CATS, CUMMINS, DETROITS, ETC.....
While I enjoy a good debate, I believe that this horse is LONG DEAD!!!
Tom

FightinTXag

03-03-2003, 12:26

TG,
>My point is, if the 8.1 can't outperform the
>Duramax on flat ground it certainly will not on
>a 6% grade pulling 10,000lbs.

Ok let me get this straight, you agree that the 8100 is capable of putting more torque to the ground. You see that the very article you quote shows the 8100 to pull hills faster. You don't believe any of this matters, but you insist because they have stopwatches showing under some circumstances somehow the duramax accelerates on flat ground quicker (which I find hard to believe) that it MUST be capable of outpulling the 8100. Even though every person with experience with both motors will tell you it ain't so? Even though the article says it ain't so? Even though physics says it ain't so?

EWC,
>OK Fightin and ZF , I have scheduled a 3 way
>conference call with you and Chevrolet so that
>you may explain to them that all the literature
>on their website , that has listed torque as ft-
>lbs , is incorrect

I never said lb-ft wasn't correct. Re-read my post. It's just as correct to say lb-ft (pound-feet) as it is to say ft-lbs (foot-pounds). We've been through this over and over.

>go all the way to the overdrive gear , you will
>see that the only one that makes more power is
>the 8.1/ZF/4.10 combination

You won't be pulling in overdrive with any combination if you're trying to get up a hill fast.

>the 8.1 runs @ almost 4000 Rpm in 3rd gear . Who
>the heck runs 60 MPH in 3rd gear ?

If you have an 8.1L you can pull a hill in 3rd gear at 3900 rpm. If you're trying to get up the hill as fast as possible, that's exactly what you'll be doing. 3900 rpms isn't much when your redline is up at 5000 if my memory serves correctly.

CPMac,
>ZFMAX, where in my figures am I going wrong. The
>8.1 will pull to around 4300 then shift and drop
>to around 2700, the Max will pull to 3100 then
>drop to 2100. The 8.1 is around 425 tq from
>2500 to 4300 and the max is 500 from 1500 to
>3000.

You have to think about the fact that when the D/A shifted at 3100, it just reduced rear wheel torque because it's now using a higher gear. Meanwhile the 8100 keeps on trucking in the lower gear until at least 4300 or so, all the while delievering more torque to the rear wheels because of the lower gearing. When the 8100 does finally decide to shift, the duramax will be close to making another shift. The 8100 will always stay 1 or 2 gears lower than the dmax using the mechanical advantage of the lower gears to deliver more torque to the ground.

RATDOC,
>IF these engines were so good at putting all
>this power down, WHY DO THE BIG RIGS EVEN BOTHER
>TO USE CATS, CUMMINS, DETROITS, ETC.....

We've said a hundred times there's more to consider than just how fast a load gets up the hill. We've all seen studies about how we can justify the $4,000 diesel cost in fuel savings alone in ~65,000 miles versus the 8100. How many times will a $10,000 diesel engine pay for itself in 500,000 or a million miles? How many long block gas engines would we go through making a rig reach that many miles when it's screaming away near the top of its rpm range? Trucking companies are in business to make money not race trucks up hills.

[ 03-03-2003: Message edited by: FightinTXag ]

[ 03-03-2003: Message edited by: FightinTXag ]

Diesel Freak

03-03-2003, 17:43

To those people still convinced the pickup will outpull the semi because it has more HP: I offer my services anytime somebody wants to do a real world comparison. Been there, done that!

EWC

03-03-2003, 20:53

Fightin , apparently Chevrolet doesn't agree with you on the torque measurements and feels that there is a certain way to have the words arranged . I quess they feel that semantics are important . You should go back and do your calculations again . Using your calculations , the Duramax puts more power to the ground than the 8.1/Allison/4.10 combo . I quess you are having a hard time believing the results . Like TG asked , how can a 300 HP combination beat a 340 HP combinastion ? I was taught to believe the results and invent a new theory . How about you ?

CPMac632

03-03-2003, 21:27

Fighting the 8.1 does not always stay 1 to 2 gears lower. That is the dumbest statement yet. What about 1st gear? You tell me how a 8.1 allison can put more to the ground (without being in low range of transfer case) from 34 mph to 41mph. It can't it is impossible with factory options. So if your wanting to compare at a certain mph then there you go that is 8 for you to work with. Sure either one can get hung in a gear in a certain loaded condition but that isn't the point. The duramax on average is putting more to the groung and you don't have to drive it like your mad at it. Up to 76 mph the 8.1 allison 4.10 outpulls the Dmax allison 3.73 at 36 different mph. That leaves 40 other mph the Dmax outpulls the 8.1.

[ 03-03-2003: Message edited by: CPMac632 ]

[ 03-03-2003: Message edited by: CPMac632 ]

FightinTXag

03-04-2003, 09:36

EWC, show me where in the Chevy literature it says explicitly that ft-lbs is wrong.

CPMac, Ok you've got me. The 8.1 obviously won't be in lower gears when they're running in first, and for a range of about 4 or 5mph you'll be in the same gear in 2nd. I was trying to emphasize that in my post where I say that "when the 8100 does finally decide to shift, the duramax will be close to making another shift." At that point I should have said FROM THEN ON "the 8100 will always stay 1 or 2 gears lower than the dmax.." But assuming we were talking about pulling a hill at close to normal freeway speeds it doesn't matter.

Anyway, here we go. Assuming the 8.1/A shifts at 4900 and the D/A shifts at 3100. They'll both be in first up to maybe 24mph. While in first the D/A will put ~5800 ft-lbs to the ground while the 8.1/A/4.10 puts ~5400 ft-lbs to the ground. Then the D/A will upshift while the 8.1 stays in first until 35mph. So for the next 10 mph (from 25-35) the 8.1/A/4.10 continues to put ~5400 ft-lbs to the ground while the D/A's output drops to ~3400 ft-lbs. When the 8.1 upshifts to second at 36mph its rear wheel torque will drop to ~3200 ft-lbs while the D/A's is still at ~3400 ft-lbs. This is the way it will remain for 5mph until the Duramax has to upshift and it's rear wheel torque drops to ~2600 ft-lbs.

8100/A/4.10 D/A
0-24mph 5400 (1st) 5800 (1st)
25-35 5400 (1st) 3400 (2nd)
36-41 3200 (2nd) 3400 (2nd)
42-55 3200 (2nd) 2600 (3rd)
(At 55 both trucks will shift)
56-70 2500 (3rd) 1850 (4th)
71-75 1750 (4th) 1850 (4th)
76-100 1750 (4th) 1300 (5th

This should be a decent estimate since the torque curves are fairly flat for the rpm range we're looking at on each engine. Whether or not the allison would shift consistently at the rpms we talked about is debatable since the allisons probably don't shift the same from truck to truck with the adaptive business.

Basically it looks like the D/A holds 400 ft-lb edge in rear wheel torque at 0-24, a 200 ft-lb advantage 36-41 and a 100 ft-lb edge 71-75. All the rest of the time the 8100 can provide AT LEAST 600 ft-lbs of torque more to the rear wheels. These points include the bulk of freeway towing speeds which is what the thread began by talking about. So if you do a lot of towing in the 0-24mph range, congratulations you're D/A will pull more of a load at those speeds than an 8.1L.

[ 03-04-2003: Message edited by: FightinTXag ]

CPMac632

03-04-2003, 10:17

No fighting your wrong again. The 8100 torque falls of fast over 4500rpm so at 4900 rpm the torque is not 425 in fact it is way less that 400 so do the comparisons fairly. The point is if you don't load heavy enough to stall either one in a gear the dmax will pull better across the board. Sure we both agree either one can be stalled somewhere and that does suck but they are both exceptionally good towing vehichles and both have their place where they are better but towing stock to stock would be more pleasurable in a dmax in most situations.

FightinTXag

03-04-2003, 10:40

Got to thinking about it and the Duramax's advantage in first gear isn't that big (if it exists at all) because it doesn't start making torque until the turbo is wound up. So for the first 1200 rpms, the dmax doesn't look like it's making as much torqe as the 8.1L (~300 ft-lbs versus ~390 ft-lbs at idle which translates to ~3500 ft-lbs versus ~5000 ft-lbs at the rear wheels). This makes sense since a D/A can't touch an 8.1L off the line. 1200 RPMS takes you to about 10 mph so for the first 10 mph the 8100 should be providing considerably more torque to the rear wheels. Once the turbo is spooled up the duramax takes over until it shifts at 25mph.

>The 8100 torque falls of fast over 4500rpm so at
>4900 rpm the torque is not 425 in fact it is way
>less that 400 ..

What curve are you looking at? The only one I know of is here:
http://www.gm.com/automotive/gmpowertrain/engines/vortec/apps/vehicle/images/l18curve.jpg
It doesn't show what it does at anything above 4500rpms. At 4500 it looks to me to be around 425 still. The minimum torque between 2000 rpms and 4500 shows to be around 425 with a peak in the middle at 455. If whatever you're looking at shows torque to be anywhere near 400, I'd still say 425 is a good average torque number for that range. Since it will spend ~2000 rpms making 425-455, it can stand to spend ~500 rpms making less than 425 and still average ~425.

>The point is if you don't load heavy enough to
>stall either one in a gear the dmax will pull
>better across the board.

Ok, if you're insisting we run both trucks in the same gear, you're right. Otherwise, you're not. If I'm traveling anywhere from 45-70mph on a hill, on flat ground, with a load, or without, and I stomp on the pedal, the allison downshifts, I'm going to have a lot more rear wheel torque available with an 8100 under the hood. I'm going to accelerate or hold my speed better than a D/A traveling the same speed with the same load.

>they are both exceptionally good towing
>vehichles and both have their place where they
>are better but towing stock to stock would be
>more pleasurable in a dmax in most situations.

Couldn't agree with you more. :D

[ 03-04-2003: Message edited by: FightinTXag ]

[ 03-04-2003: Message edited by: FightinTXag ]

[ 03-04-2003: Message edited by: FightinTXag ]

CPMac632

03-04-2003, 19:34

If you were talking about 6 speed trucks I might believe you but on the autos the convertor will let you get well above 1200rpm without even moving so there goes that theory.

EWC

03-04-2003, 21:01

Fightin , what graph are you looking at ? The GM graph looks like the Duramax makes about 350 lb-ft @ 1000 RPM and the 8.1 makes about 380 lb-ft @ 1200 RPM . In just 800 RPM the Duramax goes to 520 lb-ft and holds that number for about 1500 RPM more . That is called torque rise . It takes the 8.1 2000 RPM to get an additional 75 lb-ft of torque . If you call that an advantage over the Duramax , man do I have some swamp land for you . No , you need to do your calculations over again for the 8.1/Allison/4.10 combo . Using your formula , and I guess a good calculator , the Duramax doesn't lose to the 8.1 except in 3rd gear . But you still haven't answered TG's question : if the Duramax is only making 300 HP and the 8.1 is making 340 HP , how did the Duramax out pull the 8.1 in the 0-60 and 40-60 tests in the Trailer Life article while carrying a 1000 lbs more ? It's a simple question really . No smoke and mirrors , just a straight answer . Get with ZF on this one . And as far as the torque terminology goes , there's ft-lb ( your choice ) and lb-ft ( my choice and Chevrolet , Ford , Dodge , Cummins , Cat and Detroit Diesel ). Why don't you ask them why they choose the wording that they did ?

FightinTXag

03-05-2003, 13:48

CPMac,
>on the autos the convertor will let you get well
>above 1200rpm without even moving ...

You're right. If you're going to rev the motor with your foot on the brake on launch, you might help the D/A. The problem with that is that the torque numbers on the curve are for full-throttle. So even though you have the duramax turning 1200+ rpms, what's on the graph is not on tap when you let off of the brake because the accelerator hasn't been on the floor and boost isn't all the way up for that rpm. When you do let off the brake and punch the accelerator, it's going to take a second or two for the turbo to spool up. By that time you may be out of the 0-10mph range we're talking about. I don't know how much you're going to help the Duramax doing this so I'm not sure if it'll be enough to offset the 8100's low rpm torque advantage if you do a similar launch with it.

I really don't think it matters much because not many people do a ton of pulling at less than 10 mph. Even if you can manage to average 500ft-lbs from the Duramax in first gear you're only getting 7% more torque than the 8.1/A to the ground for the first 24mph before the duramax shifts and the 8.1 gets 59% more torque to the ground. Then the two combos are pretty close again for 5mph (36-41) before the 8100 has the edge all the way up to 70mph.

EWC,
>Fightin , what graph are you looking at ? The GM
>graph looks like ..

The 8100 chart shows ~380 ft-lbs available at the first point on the chart. It looks to me like this is around or maybe slightly less than 1000 rpms. I assume they ran this test from idle and that ~380 ft-lbs is at idle. Torque range is from 380 up to 455 ft-lbs.

The Duramax chart shows 300 ft-lbs available a the first point on the chart at around 800 rpms. Torque range is from 300 ft-lbs up to 520 ft-lbs.

>That is called torque rise . It takes the 8.1...

If you think "torque rise" is more important than a flat torque curve, I've got some ocean-front property in Arizona for you. That 80 ft-lb difference at idle rpms manifests itself through the drivetrain for a 1500 ft-lbs difference at the rear wheels.

>if the Duramax is only making 300 HP and the 8.1
>is making 340 HP , how did the Duramax out pull
>the 8.1 in the 0-60 and 40-60 tests in the
>Trailer Life article

My guess (and that's all it would be) is that the allison isn't letting the 8100 spin high on flat ground to take advantage of its higher revving. The allison will let my duramax rev all the way to 3100 rpms unloaded on flat ground taking full advantage of the entire rpm range. My 8100 never got near the redline. But acceleration on flat ground was never the topic of this thread.

Let me turn this question around. If the Duramax's torque is more important for pulling than the 8100's horsepower, how does the same article you quote have the 8100 pulling hills faster? How does everyone with experience with both of these engines attest to the 8100 being faster?

>...Chevrolet , Ford , Dodge , Cummins , Cat and
>Detroit Diesel. Why don't you ask them why
>they choose the wording that they did ?

I will right after you call API (American Petroleum Institute) and ASME (American Society of Mechanical Engineers) and let them know that the moment units in all of their codes and standards is incorrect. Maybe they'll satisfy your need to argue about this issue some more. :rolleyes:

pinehill

03-05-2003, 14:09

Fightin,

OORAH & OOAH!

Tough Guy

03-05-2003, 20:24

FightnTXag-

Quote(s) from Trailer Life:

"While both trucks have identical travel trailer tow ratings, it should be noted that this test drive was not intended as a specific head-to-head comparison between the two dissimilar engines. Readers can draw their own conclusions about comparative performance details, but we placed a priority on showing you how these new engines performed individually rather than being pitted against each other."

"Our highest-elevation test came at Sherwin Summit near Bishop, California, which tops off at 7,000 feet elevation. The Duramax 6.6L truck and trailer climbed most of the hill at 55 mph @ 2,300 rpm in fourth gear, and crested it at 53 mph @ 2,200 rpm in fourth gear, and the Vortec 8.1L made it most of the way at 61 mph @ 4,000 rpm in third gear."

This "towing test" was not a performance competition as stated in the first quote. Also note in the second quote the rpm of each truck. What would the speed of the Duramax have been in 3rd gear??

The 0-60 and 40-60 however IS a direct performance comparison between the two.....

Cheers

FightinTXag

03-06-2003, 08:51

TG,
>The 0-60 and 40-60 however IS a direct
>performance comparison between the two.....

I don't know how you figure that that quote only applies to the "hill climbs" portion of that article. The article has the following sections:

Chassis, Body, Interior
Hardware Details
On the Road
Transmission Impressions
Hill Climbs
Downhill Braking
Fuel Economy
Acceleration
Conclusion

That quote is in the Hardware Details section that precedes both "Hill Climbs" and "Acceleration" sections.

Quote:

"While both trucks have identical travel trailer tow ratings, it should be noted that this TEST DRIVE was not intended as a specific head-to-head comparison between the two dissimilar engines."

The next paragraph says:

"The TEST DRIVE covered approximately 1,360 miles of city, free-way and two-lane state highway travel, solo and towing, and ranged from 282 feet below sea level at Badwater in Death Valley, California to elevations higher than 7,000 feet. Temperatures varied from the 60s to more than 118 degrees F during the pass through Death Valley and thereabouts in the desert. "

I'd say they mean more than just the hill climbs when they're talking about the "TEST DRIVE." So that quote applies to the acceleration data as much as the hill climb results.

>What would the speed of the Duramax have been in
>3rd gear??

The fastest the duramax could've been going in 3rd gear is 55mph at redline. That's the same speed they say it pulled most of the hill at. So basically, it had the power to pull up to 55 mph in 3rd gear and then it had to upshift and lacked the power to pull any faster in 4th gear.

The 8100 was able to stay in 3rd gear and pull up to 61mph. That's the advantage that horsepower gives you.

Colorado Kid

03-06-2003, 09:08

Hey Tough Guy, you finally asked a question I can answer...we all know what the speed of the D-max would have been in 3rd gear...52 MPH, see every Pull-Off to date. ;)

I don't know why the D-max out accelerated the 8.1 in Trailer Life's test. Maybe they got the numbers backwards when they took them out of their notebook after the day of testing...stranger things have happened.

I'm content to wait till June to see what happens.

Tough Guy

03-06-2003, 18:00

1st pull-off Dmax 55mph
2nd pull-off Dmax 56mph
3rd pull-off Dmax 54mph

*This was 3rd gear with the Allison equipped trucks....(I was in each of the trucks when these numbers were made..)

If anyone recalls this is the post that started this whole thing...

All-tuned-up wrote:
Had someone pull my 42' Race car trailer the other day with his '02 8.1 gas, pulled it up a hill that my duramax would top out at 50, he did it at 75 mph! With room to move."

I call BS on this one.

The pull-off will be interesting this year because the "test" is 1 mile from a dead stop on a 6% grade. As I posted before it would seem likely from the 0-60 tests performed by Trailer Life that the Duramax will win.

Cheers

EWC

03-06-2003, 18:11

TG , did you run the Power Project truck at the hill climb ? If so , how did you do ?

Colorado Kid

03-07-2003, 15:54

TG, OK, you got me by a little...I was relying on my famously unreliable memory since we cannot read any of the Pull-Off stories any more. Sorry. I guess the D/A would have been going about 55 MPH in 3rd.

How fast the 8.1/A will be going at the 1 mile point this year is anybody's guess. It's interseting to note that 5000 RPM in second gear (1.81 ratio) with the T/C locked (tow-haul) and 3.73 gears would be about 68 MPH. (or at 4200 RPM (Peak HP) in the same gear is 57 MPH)

For 4.10 the speeds are 62/53

In other words, I think the outcome will be pretty dramatic one way or the other...either the 8.1 won't be able to accelerate the load in 2nd gear, and will finish somewhere around 40 MPH, or I'll have to change my signature. ;)

Maybe they'll split on the ET and terminal velocity...with that load on that hill the D-maxes are very impressive from 0 to 20, and I think the 8.1 will spend more time getting off the line....The clock doesn't start until forward motion does, so it's not like throttle response is an issue...the D/A's are making boost when the brakes are released.

I kin hardly wait till June. :D

additive

03-07-2003, 23:48

Tough Guy,

Evaro hill is just too easy for all these rigs - we need to take to the hill you climb when going into St. Ignatius (or however it is spelled).

Of course now that I have the powerstroke I can really kick some hiney -- just ask the guys at The Diesel Stop. :D :D :D
Additive

EWC

03-10-2003, 16:55

Well Fightin , I was going to reply to your last post but I couldn't stop laughing at your previous assumptions/conclusions with all their inconsistence calculations . In one reply you talk about the torque or power that the Duramax has over the 8.1 at low RPM's , the next you have the 8.1 and the Duramax even and the final reply you state that the 8.1 has a huge advantage over the Duramax at low RPM's . Man , the spin you put on things !! Are you sure you don't work for a politician doing damage control ? Wait a minute , you work in Texas at an oil refinery , are bored with your job, go online during work hours and don't know the correct terminology for torque . Do you work for the big E that got in so much trouble recently ? When you can actually read a graph correctly , like the one at the bottom of the Duramax 6600 section which shows HP and torque (in lbs-ft ) , and make some intelligent calculations please post again . Otherwise ....

FightinTXag

03-10-2003, 19:54

>with all their inconsistence calculations

There is no inconsistency in my calculations. Show me one instance where the numbers or formulas change.

>In one reply you talk about the torque or power
>that the Duramax has over the 8.1 at low RPM's ,
>the next you have ...

I NEVER said ANYTHING about the Duramax having an advantage at low rpms. I don't know where you got that.

I did the calculations based on SPEED using CPMac's average torque numbers and the duramax would have an advantage using his assumption that the Duramax would average 500 ft-lbs throughout the rpm range. Then I thought about the fact that my 8100 would royally embarass my dmax off the line and realized the rpm's won't be up where the Duramax is making good torque when taking off from a start in first gear. Don't believe me? Find somebody with an 8100 and race him from a stoplight, or go test drive one. There's no way the Duramax has more performance in the first 10 mph or so.

Look at the torque curves provided by GM anybody can see that the duramax is making less torque than the 8100 until 1200 rpms.

>don't know the correct terminology for torque.

I've already told you to call ASME and API and let them know that the great and powerful EWC says that their codes and standards are all wrong. Have you made that call yet? Please go argue with them. I'm tired of fooling with you.

>When you can actually read a graph correctly

I don't know what it is that you think I'm reading incorrectly. It's as plain as the nose on my face that the 8100 is making 380 ft-lbs of torque while the duramax is making 300 ft-lbs at idle rpms.

>Do you work for the big E
>Are you sure you don't work for a politician
>doing damage control ?

No, I don't work for Exxon. I don't work for any oil company. I work for an engineering and construction company.

But, let me see if I can figure you out...
You being, a nonsensical, abrasive jerk from Maryland, insisting to argue on things you don't seem to have a grasp on, making politcal references and accusations, falsely attributing comments to people...
Yup you must be a Kennedy! ;)
(No offense JK)

Kennedy

03-10-2003, 20:18

I got my doors blown off at a light by a 2500 HD gasser the other day. :eek: I heard a squawk and he was gone!

I got elbowed hard when I tried to get his attention and ask if he'd like to go again for $500. This time, I'd actually TRY, as I really didn't even realize he was there...

FightinTXag

03-10-2003, 23:57

It just dawned on me that EWC may have been referring to Enron. To the best of my knowledge Enron never owned or operated any refineries, just pipelines for their energy trading business.

JK,
I'm sure you would've thoroughly punished that gasser and made him a little lighter in the pockets, but I guess the hard elbow made all bets null and void.

EWC

03-11-2003, 05:51

Didn't even bother to look at the graph at the bottom of the Duramax 6600 section , under power specs ? That's pretty clear . Not much room for your tactics . Notice the terminolgy . Guess the Diesel Page is wrong to .

FightinTXag

03-11-2003, 09:47

>Didn't even bother to look at the graph at the
>bottom of the Duramax 6600 section , under power
>specs ?

If you're talking about this torque chart:
http://www.62-65-dieselpage.com/news3.htm
It looks to me to be the same as the GM one I've been looking at here:
http://www.gm.com/automotive/gmpowertrain/engines_cartruck/diesel/66lb7_torque.htm

The one you're talking about is a little smaller than the GM chart. Maybe that's why you're having trouble.

>Notice the terminolgy . Guess the Diesel Page is
>wrong to .

On Feb 20 I posted:
Torque is measured in ft-lbs or lb-ft. That would be foot-pounds or pound-feet.

On Feb 23 I posted:
Bottom line is you can say ft-lbs or lb-ft and it means the same thing.

On Mar 3 I posted:
I never said lb-ft wasn't correct. Re-read my post. It's just as correct to say lb-ft (pound-feet) as it is to say ft-lbs (foot-pounds). We've been through this over and over.

Obviously, everything that's been said here supports the fact that ft-lbs and lb-ft are both correct. As you point out, GM, Ford, and Dodge use lb-ft. So does NEMA (National Electrical Manufacturers Association). This is perfectly fine and correct. ASME and API and all of the engineering software we use prefer ft-lbs. This is fine and correct.

You are the only one insisting anybody is wrong.

Kennedy

03-11-2003, 09:53

I believe the technically correct term is lb/ft as in how many LBS per foot of moment arm are applied vs. how many ft per lb...

Not sure if this is a potato potatoe pototo thing, or if there is a TRUE technical difference...

ZFMax

03-11-2003, 09:56

EWC, your obsession with convincing people to use a different terminology is almost comical smile.gif What does it matter anyway? Who cares?

BTW, you can add Dynojet to the list of people to plead your case to, I noticed that Winpep printouts say "ft/lbs" on them. Best of luck!

Fightin', my hat's off to you, your patience exceeds mine by several orders of magnitude. I don't think you'll succeed, though, you're dealing with an emotional stake in the notion that basic laws of physics must be incorrect. They'd rather make that argument than question the data they have, and that says it all. There's really not much point in trying to help someone understand once they've taken that position.

FightinTXag

03-11-2003, 12:41

JK,
It's not pounds PER foot or feet PER pound. This would imply that torque was calculated by dividing the force by the moment arm or vice versa . If that were the case and you had 300 pounds on one foot of moment arm, you'd have 300 pounds PER foot of torque.
300lbs/1ft = 300 lbs/ft or instead
1ft/300lbs = .0033 ft/lb

If the momment arm was doubled to two feet, then the force would have to be doubled to 600 pounds to get the same torque.
600lbs/2ft = 300 lbs/ft or
2ft/600lbs = .0033 ft/lb

This doesn't make sense.

If you're trying to get a bolt off and you double the moment arm by using a cheater bar and double the force, we all agree that you'll be getting more torque on the bolt, not the same amount of torque.

Torque is instead the product of the force and the moment arm. If you have 300 ft-lbs or 300 lb-ft of torque and you double the moment arm or double the force, you will double the torque.
300lbs * 1ft = 300 lb-ft
300lbs * 2ft = 600 lb-ft. or
600lbs * 1ft = 600 lb-ft.

If we double both the force and the moment we will quadruple the torque.
600lbs * 2ft = 1200 lb-ft.

This makes a lot more sense. Because the order of the dimensions doesn't matter when calculating torque we can see:
300lbs * 1ft = 300 lb-ft and
1ft * 300 lbs = 300 ft-lbs.

So lb-ft versus ft-lbs is all a matter of preference. 300 ft-lbs tells us that a one foot moment arm will have 300 pounds applied. A two foot moment arm will have 150 pounds applied and so on.

EWC

03-11-2003, 16:27

ZF , it is comical , isn't it . My first post , on the wording of torque , was really an observation . The terminolgy of ft-lbs for torque is a misnomer , that is a name wrongly or unsuitably applied to a person or object . I mean think about what you just said about physics and understanding the laws . The formula for torque is force multiplied by a moment arm . It is not torque = moment arm multiplied by a force , which is what you are saying with ft-lbs . To get a product from the formula you multiply the numbers but you have also assumed that because you can multiply the numbers and get a product you can also do that with the words describing the numbers . Because of that assumption you feel that the order in which the words appear in the equation is irrelevant . How do you multiply two words ? You can't . The consistency is in the formula i.e. Torque=force multiplied by length , the metric system N-m , the english system lb-ft . Should we just abandon the laws of physics just because we have misused the labeling of the numbers units ? This is really a moot point since someone a long time ago decided that the definition of torque was lb-ft . It's almost like debating the definition of horsepower . It also has already been defined . When Fightin first described torque in an equation , how many responses do you think he would have gotten if he had stated that torque = moment arm x force ? Do I know what you are talking about when you say ft-lbs ? Yes . My only point was that the use of ft-lbs to describe torque was a misnomer . Am I on a crusade to make everyone aware of that ? No . It was just an observation . And not to add fuel to the fire , but Fightin has already said that ft/lbs is ft divided by lbs and that is incorrect .

VA_Dmax

03-11-2003, 16:57

Im not even going to jump into the whole HP vs Torque and what truck does what better. But I will jump in on the units and back FightinAG. When you multiply two numbers (example 100 lbs * 1 foot) each with a respective unit, you multiply the "word" (UNIT) also and see a result of 100 lb*ft or 100 ft*lb. Either way is the same, just like saying 1*100 or 100*1 you magically get the same number, 100. However, the measure l/100 is not the same as 100/1, therefore the order of ft/lbs or lbs/ft is NOT the same. Say I had a 100 lb load of manure in the bed of my HD that is 1 square yard in area (for easy math). I would have 100lb/square yard, and that is not the same as 100 square yards/lb. And as FightinTX has said, Torque is a measure of twist, or a force multiplied by the length of the effective lever arm. Not a measure of load/length or length/load. Just my 2 cents, if you dont like it, I just ask that you tell me nicely to go dump my 100lbs of manure somewhere else. Thanks :D

EWC

03-11-2003, 18:05

Fightin , 3/4/03 - " basically it looks like the D/A holds 400ft-lb edge in rear wheel torque at 0-24 , a 200 ft-lb advantage 36-41 and a 100 ft-lb edge 71-75 . All the rest of the time the 8100 can provide AT LEAST 600 ft-lbs of torque more to the rear wheels . These points include the bulk of freeway towing speeds which is what the thread began by talking about . So if you do a lot of towing in the 0-24 range , congratulations you're D/A will pull more of a load at those speeds than an 8.1 . " Also on 3/4/03 - " Got to thinking about it and the Duramax's advantage in first gear isn't that big ... " So it looks like you admit the Duramx has the advantage up to 75 MPH . Did you or did you not write these quotes ?? You also didn't get the point with the graphs , that is the graph , in the Duramax 6600 section , goes down to maybe 800 RPM but crosses the 1000 RPM line at 350 lb-ft of torque and looks like it continues up to 1200 RPM with 420 lb-ft of torque . You said that the 8.1 makes 380 lb-ft of torque at 1200 RPM . Where is the low RPM torque advantage that you say the 8.1 has over the Duramax . That's what I mean when I say that you can't read a graph correctly . The graph in the Duramax 6600 section does not leave any of the numbers open to your skewed logic . You also say that the 8.1 has an 80 ft-lb advantage that multiplies into a 1500 ft-lb force at the rear wheels . I just proved that the Duramax has the advantage but lets look at your numbers . 80 lb-ft x first gear ratio/Allison( 3.10 ) x rear axle ratio(4.10 ) = 1016 lb-ft . I thought you said that it was 1500 lb-ft advantage . That's off by almost 30% . Are these acceptable loses where you work ? I hope not . You also make the statement that the 8.1 puts more power to the ground than the Duramax and that is NOT a true statement at all ! Do the math if you can . What about the fact that the Duramax had almost a 1000 lbs more weight to pull and yet it still beat the 8.1 from 0-60 and 40-60 ? No it was not the extra weigh of the diesel , the trailer was loaded more . Read the article again . You also run your calculations with the Duramx at its peak RPM but run the 8.1 to a higher RPM than its peak by almost 700 RPM . Same with the dyno conclusions . The turbo doesn't spool up until 1200 RPM ? The dyno doesn't know or care if the turbo is spooled up or not . You make a lot of assumptions that do not compare equally across the boards . If you run one engine to its max. RPM then that is where you run the other engine . The great equalizer is the running of the trucks in real world conditions and that is why the data from the 0-60 and 40-60 tests is relevant . You also state that the 8.1 has a flat torque curve and that is very important . Hmm , the 8.1 torque curve varies by 75 lb-ft over about 3000 RPM and the Duramax varies by 3 lb-ft over 1500 RPm . If you could read the graphs you would see that but obviously that escapes you . Next time be sure of what you write . Any one can go back a few pages and see what you did write .

FightinTXag

03-11-2003, 20:07

>Fightin , 3/4/03 - " basically it looks..
>Also on 3/4/03 - " Got to thinking about it..
>Did you or did you not write these quotes ??

Yes I did. So if posting something and then realizing that the assumptions used weren't totally accurate for that first gear means I'm doing "inconsistent calculations" then I guess I'm guilty as charged.

The fact remains that the duramax won't be putting out more torque than the 8100 until around 1200 rpms. This doesn't play much of a role except in first gear because you'll never be at <1200 rpms in any other gear during a full throttle pull.

It really doesn't matter much anyway. Look at the rest of the speeds. Nobody pulls a lot in first gear at full throttle and less than 1200 rpms. Is it really worth this much energy?

>So it looks like you admit the Duramx has the
>advantage up to 75 MPH .

Nope. Never said that. Again, I don't know where you got that. It's really frustrating having to post the same thing over and over and correct you when you try to put words in my posts. Please read carefully.

>You said that the 8.1 makes 380 lb-ft of torque
>at 1200 RPM

No I said the first point on the 8100 curve looks to be 380 ft-lbs. I'd assume it's at idle. It looks to be at 1000 rpms or mayble less. Definitely not 1200 rpms. So I'd say that the duramax makes less torque up to 1200 rpms. If you don't think so, I don't really care.

Everything you said about the duramax curves looks accurate.

Again who really cares though. Not much time is spent at less than 1200 rpms in first gear at full throttle.

The only reason I even brought it up was because anybody with experience with both of these motors knows the 8100 has much more torque and throttle response off idle. The 8100 (and even the 6000 I'd bet) can light 'em up with no brake. My duramax can't.

>You also say that the 8.1 has an 80 ft-lb
>advantage that multiplies into a 1500 ft-lb
>force at the rear wheels . I just proved that
>the Duramax has the advantage but lets look at
>your numbers . 80 lb-ft x first gear
>ratio/Allison( 3.10 ) x rear axle ratio(4.10 ) =
>1016 lb-ft . I thought you said that it was 1500
>lb-ft advantage . That's off by almost 30% . Are
>these acceptable loses where you work ?

380 * 3.1 * 4.10 = 4830 ft-lbs
300 * 3.1 * 3.73 = 3470 ft-lbs

The difference is 1360 ft-lbs which is "almost 1500 ft-lbs." That's what I said, "almost 1500 ft-lbs."

>You also make the statement that the 8.1 puts
>more power to the ground than the Duramax and
>that is NOT a true statement at all ! Do the
>math if you can .

I have. It's all over the preceding pages of this topic. It's what you've been dissecting and trying to disprove.

>What about the fact that the Duramax had almost
>a 1000 lbs more weight to pull and yet it still
>beat the 8.1 from 0-60 and 40-60 ? No it was not
>the extra weigh of the diesel , the trailer was
>loaded more

Well, you're half right. The duramax setup in the article was 960 lbs heavier. 420 of it came from a heavier trailer. The the other 440 is due to the extra weight of the engine and the fact that the duramax in the test was a crew cab while the 8100 was an extended cab.

I've already taken my best guess at why the 8100 was slower in acceleration. From my experience the allison wouldn't ever let my 8.1L get near redline on flat ground.

>You also run your calculations with the Duramx
>at its peak RPM but run the 8.1 to a higher RPM
>than its peak by almost 700 RPM . If you run one
> engine to its max. RPM then that is where you
>run the other engine .

I assumed both engines would be shifting at 100 rpm less than redline. If I remember correctly the 8100 redlines at 5000. The duramax redlines at 3200.

>Same with the dyno conclusions . The turbo
>doesn't spool up until 1200 RPM ?

Again, that's not what I said. I said the turbo hasn't spooled up for the given rpm unless the pedal is on the floor. If you're launching with one foot on the brake and you're not moving or burning rubber, the pedal must not be on the floor. The turbo won't be spooled up for the given rpm and all the torque on the curve will not be available for a second or two after the pedal is mashed.

>The dyno doesn't know or care if the turbo is
>spooled up or not .

The dyno does care (as much as an inanimate object can) if the pedal is on the floor and if the turbo is spooled up for the rpm. Read some of the posts on this sight about dyno runs. They never look at first gear runs because the turbo isn't spooled up for the lower rpms.

>also state that the 8.1 has a flat torque curve
>and that is very important . Hmm , the 8.1
>torque curve varies by 75 lb-ft over about 3000
>RPM and the Duramax varies by 3 lb-ft over 1500
>RPm

Well here's a new one for you. This time instead of putting words in my posts you're just taking my statements out of context. I guess that's progress.

Anyway we were talking about the low-rpm thing and you were bragging about the duramax's "torque rise." I just said that "torque rise" wasn't something to be valued like a flat torque curve. I didn't say the duramax's curve wasn't flat. It is once it gets above 1500 rpms. But below that, which was the topic we were discussing at the time, the 8100's curve is flatter.

But if you insist on comparing the torqe curve flatness for the two motors, you should look at the entire rpm range for each motor (instead of a snapshot of a narrow range like your numbers use) and look at the torque range that corresponds:
The 8100's torque varies about 75 ft-lbs over its 5000 rpm range.
The duramax's torque varies about 220 ft-lbs over its 3200 rpm range.

I'd really like to let this go, but I feel like I have to keep chiming in to keep you from making up BS I supposedly posted.

[ 03-11-2003: Message edited by: FightinTXag ]

sdaver

07-21-2003, 12:23

SO GUYS HOW DID THE 8.1 FARE AGAINST THE DMAX? I THINK I KNOW :D DAVE

EWC

07-21-2003, 18:34

Personally , I can't wait to see what line of reasoning they try to apply this time around .

NWDmax

07-21-2003, 19:19

I spoke with a 8.1 owner at a campground this weekend and he just ogled my truck while expressing his dissapointment over what he bought.
He said the 8.1 had good torque but felt the acceleration was lacking.
I think a Dmax will be in his future! :D

Tough Guy

07-21-2003, 22:17

I was wondering when this thread would rear its ugly head....

The 8.1 was powerful and did put up a good fight, but the Duramax beat it, with 10,000lbs behind them both it is no contest.

The complete story will be available for reading very soon.

Cheers

DmaxMaverick

07-21-2003, 22:25

Looks like "fuzzy physics".....

JoeyD

07-22-2003, 14:54

Originally posted by NWDmax:
I spoke with a 8.1 owner at a campground this weekend and he just ogled my truck while expressing his dissapointment over what he bought.
He said the 8.1 had good torque but felt the acceleration was lacking.
I think a Dmax will be in his future! :D My brother has a HD with the 8.1 and acceleration is far from lacking towing or not.

EWC

07-22-2003, 17:42

Yep , fuzzy physics and silly science . The theme song has got to be " Twist and Shout " . Oh well , what can you expect from someone who thinks 420 + 440 = 960 .

NWDmax

07-22-2003, 19:40

Joey D;Just passing on what a 8.1 OWNER had to say about his truck.He walked over to my campsite and offered the info with no prompting from me. ;)

Spartus

07-24-2003, 00:57

I've driven both trucks with a car trailer on them. The Dmax actually had a heavier car on it. The Dmax hands down puts the 8.1 to shame.. Stock for stock with no changes on each the Dmax will slaughter a 8.1. ;)

-Tom

EWC

09-06-2003, 10:48

Now that the article on the running of the bulls in Montana ( Power Pull Off ) has been posted , I'd like to hear opinions as to why the 8.1 , with a 4.10 rear no less , didn't better the Duramax time .

afp

09-06-2003, 13:05

I think guys are getting confused here. There are two distinct concepts. The first is efficiency of a given combination for its intended application. In this area the DMax--as it comes from the factory--wins hands down. That's why we all bought one.

However, it is a mistake to confuse efficiecy of combination with power output. My 610 HP (dynoed) drag race car's first pass was in the 12 sec range--way under it's potential, even for a 3200 lb combination. By progressively loosening the stall of the converter (from 5800 to 6400 rpm), changing gears from 5.83 to 6.20), and experimenting with shift points, carb, and cam; I got the car into the 10.70s. I did not increase the power output of the motor, I just made the car more efficiently put it's power to the ground. I still had another 1/2 sec in the car, but I was out of time and money at that point.

The second concept is how power is measured. Power output is measured in terms of HP, not torque. Torque is pure force. You can get 300 ft lbs of torque with a big torque wrench at zero rpm. Now HP is that force under rotational movement, and the faster you spin that wrench while maintaining 300 ft lbs of torque, the more power it takes.

You can get 300 HP at 5250 rpm and 300 ft lbs of torque. You can also get 300 HP at 2625 rpm with 600 ft lbs of torque. It takes the same amount of overall power to do either. Yes, it takes more force to get 300 HP at 2625 rpm, but becasue it is spinning at half the rpm, the total effort required to get 300 HP is the same. However, in a truck, you need different gearing for each combo to most efficently get that 300 HP to the tires.

The 8.1 makes it's power significantly higher than does the DMax. However, it's common for them both to have similar gear ratios. The 3.73 ratio is very good for the DMax, which makes peak power at 3100 rpm, and the 8.1 at 4200 rpm. For the 8.1 to be geared in an equivalent manner to a DMax, it would need over a 5.00 gear, which is not offered.

Now, the above gearing is assuming keeping the motor at peak HP is optimum. My drag race car needed to be shifted 1000 rpm over peak HP, and at least 2000 rpm over peak torque, to make it's quickest runs. As such, we'd have to test for optimal gearing for either combo.

The bottom line, is in trucks of the same weight, a 340 HP motor will out power a 300 HP motor, assuming both are geared optimally.

As to the semi. The reason they put high torque, low rpm motors in semis is because of longevity and efficiency. This is a much greater concern than overall power output. Which trucks in unlimited tractor pulls have the best pulls? Those with big Cummins diesels in them or those with blown alcohol motors?

Blaine

Lawnboy

09-06-2003, 14:29

I feel that the 8.1 was a VERY close contender. Withen 2 mph of a D/A. I'm sure with more runs to average out, you could get the 8.1 to beat a D/A stock. Remember, all the D/A were 2500's and the 8.1 was a Dually. That extra weight when hill climbing/racing is a biggie!

I'm not bashing the D/A. Heck its a HotRodders dream vehicle. $1000 bucks in electronics, and your in the high 13's with a 6K+lb truck!

With the 8.1's torque management hinderance and maybe a owner that didn't want to sweep up pieces of his drivetrain off of the highway, no one really knows what its capable of.

Just have to be happy that GM has TWO very POWERFULL versions of a great truck.

I'd love to see all versions of GM's trucks all with 30K miles on them in different combinations of drivetrain. 2500, 3500, Suburban, Reg, ext, Crew, Short, long, 4x2, 4x4, 6.0, 6.6, 8.1, Allison, 4L80, 3.73, 4.10, you get the idea. Have them all do 3 1/4 mile runs, 3 uphill tow challenges. Then crunch all the numbers. Would make for a great Feature Article.

JoeyD

09-06-2003, 17:22

Lawnboy , I agree with your post 100%. While the 8.1 did not beat the D-Max in the pull off it was very close. Close enough to where you can't say it was blown away like some would have you think. Try running the test at sea leval and see what happens. I am very close to sea leval and there is a 13% grade near by, would make a great test.

ZFMax

09-08-2003, 10:12

afp is exactly right with his comments.

I think all you guys who think torque by itself is a performance metric should just leave your trucks in first gear all the time. You have FAR more torque at the rear wheels in first gear than you do in any other gear. Better yet, put it in first and run in 4 low range, now you're talking torque!

Just stay in the right lane, please ;) Because some us know that wheel rpm matters too, and ultimately what matters is how much of both we have at the same time.

Colorado Kid

09-08-2003, 11:38

Originally posted by Joey D:
Lawnboy , I agree with your post 100%. While the 8.1 did not beat the D-Max in the pull off it was very close. Close enough to where you can't say it was blown away like some would have you think. Try running the test at sea leval and see what happens. I am very close to sea leval and there is a 13% grade near by, would make a great test. My thoughts exactly!

My sister lives in Acton, MA, so I've got a place to stay nearby . . . I'll bring the D-max 6 speed, who's got the 8.1? :D

The 8.1/Allison is as close to the D/As as the D/As are to my truck in Missoula (About 3300 feet elevation, I just checked). If the 8.1 will make 10% more power at sea-level than at 3300' it'll pull ahead of the D/A . . . and the chances are very good that it will make at least 10% more power.

SS396

09-08-2003, 13:19

Now if we can only find a long hill that stays at sea-level smile.gif

The 5-20 mile 6-10% grade hills over the mountain passes out here in the West never start a sea-level and in most cases go much higher than 3300 feet. These are the hills I care about.

I admit the engines are close and was surprised the 8.1 didn't beat my butt (mine was the stock '03 DA). I think people would be happy with either combo. One would expect the 8.1 to out-perform, more horsepower, and 1.5L more than the DMax

Me, I like the DMax and it's 12 MPG and lower revs, pulling a 10,000# 5ver over those mountain passes.

JoeyD

09-08-2003, 17:32

Colorado Kid, My brother just happens to have an 8.1 truck. We have a trailer and the hill all you need to do is come on down.

afp

09-08-2003, 18:13

I'd like to see someone put a Vortech, intake, exhaust, and gears in a 8.1 and see what it does................

Crud, I'd like to see the same thing for a GM 6.0.

Blaine

Colorado Kid

09-09-2003, 08:47

Originally posted by Joey D:
Colorado Kid, My brother just happens to have an 8.1 truck. We have a trailer and the hill all you need to do is come on down. Uh oh :eek: I think I've been called out.

Um, I really didn't have a week off planned for the round trip drive to Mass. I'll have to bring this idea up to my wife. :rolleyes: Did I mention I'm in school right now? And working on a research project in my spare time?

Anybody who lives a little closer to Joey want to stand in for me? Please!

Seriously we're already planning to travel as far east as Sewanee, Tennessee in May, and I suspect that a visit to my sis could be tagged on to that trip, but I don't think I can get there (with the truck anyhow) any earlier than that.

When I pulled the hill I left home at 10:00 PM on Thursday and was back by 5:00 PM on Sunday, and my dad says next time he'll meet me at the other end of my marathon rather than going with me as he did that time. . . . and that was only about 30 hours of driving. MA is more than twice as far from home. If I don't take the boys (ages 5.5 and "almost 3") my wife will kill me when I get home, and if I do take them I'll kill myself, or them, if I try to make the one-way in 2 or 3 days. I love 'em, but that's too far to go with them at this point.

Joey's got the hill, the 8.1L and the trailer. . . come on, somebody with a stock D-max take him up on the challenge! I'll pay for dinner for both of you if it happens, no matter who wins.

Bigwheel

09-13-2003, 22:28

OK, someone please let me know where the pull-off will be located.... Thanks :rolleyes: :eek:

Colorado Kid

09-15-2003, 06:28

Originally posted by Bigwheel:
OK, someone please let me know where the pull-off will be located.... Thanks :rolleyes: :eek: Apparently somewhere near Arlington, Mass.

A visit to my sister in Acton (Mass) is now on the itenery for next May, my wife and sons are coming along. :cool:

Anybody going to do this sooner?

JoeyD

09-15-2003, 11:28

The hill and trailer will be waiting for you. When the time gets closer I will see about having some other beefed up trucks to run the hill.

jeff800

09-16-2003, 05:56

6 pages later, What was the topic?

Colorado Kid

09-16-2003, 06:36

8.1 vs D-max, still is. :D

Tough Guy

09-16-2003, 16:30

Lawnboy and all-

If you go back and read the post that started this topic......

"Had someone pull my 42' Race car trailer the other day with his '02 8.1 gas, pulled it up a hill that my duramax would top out at 50, he did it at 75 mph! With room to move."

"Anybody did any other comparison's? My max is stock- no chip. What gives?"

As a matter of fact we did...

http://www.thedieselpage.com/features/03pulloff.htm

You can make all the excuses you want, (gearing, the truck was a dually it weighed a little more, elevation, the 8.1 had a headwind....whatever.)

The truck was run like all the others, on the floor till the end. In fact we ran the 8.1 twice, guess how fast it was the second time...53 mph go figure. :eek:

You can change the gear ratios, add a supercharger, or take off all the sheet metal and just drive the chasis with a seat and steering wheel. But here in the real world with over-the-counter trucks the Dmax is better able to pull a load uphill than the 8.1...

Obviously this debate could go on forever, but the odds and facts are in favor of the Dmax. PERIOD!

Cheers

afp

09-16-2003, 19:10

.................and a 340 HP motor is ALWAYS more powerful than a 300 HP motor, regardless of torque output. :eek: :eek: :eek:

Blaine

JoeyD

09-16-2003, 19:39

But here in the real world with over-the-counter trucks the Dmax is better able to pull a load uphill than the 8.1... :confused:

Tough Guy, You think the 8.1 in a dooley 3500 being so close to the 6.6 in a 2500 single wheel is the fair and end all tests? Thats crazy. Where is this real world that only you live in? The times were to close as well as the speeds.

Obviously this debate could go on forever, but the odds and facts are in favor of the Dmax. PERIOD! If you say so.

SS396

09-17-2003, 05:54

You think the 8.1 in a dooley 3500 being so close to the 6.6 in a 2500 single wheel is the fair and end all tests? Thats crazy

Well the SRW 2500HD in this story weighs 7,300# and has 3.73 gears, what does a 8.1 DRW 3500 weigh. I would say the gearing offsets any weight increase, I think the test is fair.

In my view the performance of each are the same, it's all about preference. I prefer the DMax and it doesn't matter to me who wins. Mine won't stay stock much longer, so it's really a moot point.

EWC

09-17-2003, 14:10

Blaine , how do you figure a 340 HP motor is stronger than a 300 HP motor ? Were you the one who posted that if the technology was the same for each engine ( 4 valves , turbo , etc ) then the larger engine would always win ?

afp

09-17-2003, 19:05

EWC,

Because 340 is a higher number than 300, and horsepower, not torque, is the true measurement of power. Reference my 09-06-2003 03:05 PM Post on this page for a more detailed discussion.

I'm pretty sure I have posted that with an equal level of technology, the larger engine has the potential to make more power. However, that is not an original idea on my part, it is an old and well understood principal often heard as "there is no substitute for cubic inches".

Blaine

EWC

09-17-2003, 19:31

Yes , I'm aware that 340 is larger than 300 . I thought that you had a more involved answer than just looking at the numbers .

I see that you have some drag racing experience . Would you like to compare a 500 cube Pro Stock engine to a 500 cube Super Comp engine and tell me which one will be the " stronger " ? Both have 2 valve heads , roller cams , etc. but I wouldn't want to try and qualify with the SC engine in PS .

I still don't follow you on how a " weaker engine " managed to beat a stronger engine at the Pull Off . Did the Duramax have a good day and the 8.1 have an off day ? Or could it be that you have no evidence to support your theory that more HP will beat less HP ?

KevinK

09-18-2003, 06:36

What was the elevation of the pull-off? 3k feet or so? If it was and if you believe that a normally aspirated engine loses 3% of its power for every 1k feet of elevation, then the 8.1 was putting out 91% of its rated power (340 x .91 = 309). Since the turbocharged DMAX is not nearly as affected by altitude, both engines were running almost identical power. The difference is in the noise.

In Colorado, a normally aspirated engine cannot compete. At sealevel, it's a different story.

Kevin

SS396

09-18-2003, 11:07

KevinK, I think you are right but the difference will still not be significant. Sure the 8.1 may out-pull the DMax at sea level, I guess one could assume by 10% increase, probably beat it by a couple of MPH.

Surely not by 25MPH as this thread started with.

KevinK

09-18-2003, 11:23

SS396,

I did not mean to imply that I thought the 25MPH difference was right or wrong. My only point was that elevation has a significant impact when comparing a turbocharged engine to a normally aspirated engine.

By the way, A 25MPH difference does seem extreme.

Kevin

SS396

09-18-2003, 11:27

Kevin, I didn't mean to imply you did, just my comment on the thread. smile.gif

I agree with your comment on altitude.

Pat.

afp

09-18-2003, 17:53

EWC,

A 500 CI Super Comp motor motor is not anywhere near the same level of technology as a 500 CI Pro Stocker. They are not even built for the same purpose. There is more to the technology of an engine than number of valves and style of cam.

The DMax is not a weaker engine. It simply makes less HP in stock form. However, as I posted earlier, the DMax is much nearer it's optimized form in a stock truck than is the 8.1. The DMax is more efficient at putting it's 300 HP to the ground in a 3.73 geared 2500 than is an 8.1 in a 3500 with 3.73 or 4.1 gears.

Quote:

"Or could it be that you have no evidence to support your theory that more HP will beat less HP?"

It is not a theory that more HP put to the ground--given all else is equal--will bet less HP. That is a fact. To question that is to deny the laws of physics and call into question real world results from decades of engine performance development. To go faster with the same amount of weight, you need more HP.

I do not know how much experience you have had messing with gear ratios. Gearing is a huge factor in acceleration. I dropped almost 2 sec off my last drag car by changing gearing and the convertor. The power output of the engine did not change, but the amount of HP put to the ground increased dramatically.

Blaine

EWC

09-19-2003, 17:06

I don't have much experience with gearing , just a 68 Camaro that was all steel , except for the glass hood , 8 pt roll bar , 454 + .060 , 9 inch Ford with 4:88 or 5:13 gears and a Doug Nash 5 speed with a Long vertigate shifter . I ran a box stock 850 on a Dart intake or a couple of different tunnelrams with 660's up to 1050's . Best et with the single 4 was in the high 10 teens @ 136 MPH . The tunnelrams were good for mid 137 MPH and a best of 10.05 . 60 ft was poor and around 1.45 to 1.52 . No tubs and 13 inch wide slicks . Left the line @ 6400 and should have been higher . Never saw the tach until 5 th . So no , I don't have any idea about gearing .

The one problem that I have with the statements that you and ZF have made is that they are blanket statements that cover a broad range of items that are never mentioned until someone brings the statements up . You never mentioned that the technology was different between the PS and the SC motors . My point was that according to you , both had 2 valves and a roller cam , etc so there should be no difference in the power outputs , which of course there is . The way that the 2 engines get to 500 cubes is vastly different and that is critical . One theory is the big bore and short stroke and the other is to increase the stroke . Both have very different power curves and needs as well . None of this was mentioned in your claims .

You have also forgotten to even mention torque , almost as if this aspect of power ratings has NO effect and the sole measure of an engines power is strictly HP . Again , this is another blanket statement that does not seem to be supported by the tests that were done .

There is no substitute for cubic inches is a very interesting statement as well . I don't suppose you remember when Buddy Ingersol had the turbo V6 in Pro Stock and took on the 500 cube engines and totally destroyed the class . Again , another blanket statement .

So what we have so far :

1 340 is greater than 300

2 8.1 is bigger than 6.6

Using your above statements and logic , there should be no way the 8.1 will lose to the 6.6 in the hill climb . The results prove otherwise . I say because of greater torque . What about you and ZF ?

afp

09-19-2003, 19:12

EWC,

My own experience with gearing is limited as well. I have messed with gears/converters in just three different vehicles. One car had three sets of gears--5.83, 6.0, and 6.2. With this car, I fooled around quite a bit with gear ratios, three different engines, several converter stall rates, three different carbs, and several cams. This car's last motor was a 12-1 flat-top 350. The car weighed 3200 lbs empty. The small block is very torque limited, and the only way to make it run was by loosening the converter and moving to the 6.20 gears. I saw first hand in a very dramatic way what having the proper final drive ratio does to acceleration.

The "average Joe" small block racer told me I had too much gear and converter, but the more I loosened the converter and deeper I geared the car the quicker it went. The motor was a naturally aspirated, flat-top, 12-1 350 with a single 4bbl. The car weighed 3200 lbs, had a 'glide with a 1.90 low, a 4-link, and a Ford 9". The chassis was Superstock legal, but I did not have enough funds for a class-legal motor.

My car ran a best of 10.70 @ 124, which was a 1/2 sec under it's potential--I needed to use shorter tires to fix my launch, and narrower tires so they wouldn't drag the car down past the 1/8 mile. 60' times were way off--1.6s if I remember correctly (I can't find my old time slips), and 1/8th mile times were indicative of a much quicker/faster pass--6.8 and change at 100 mph on the 10.70 pass. I launched at 6400 rpm, shifted at 8000, and crossed the lights at 8500.

There is no question your 454 made more torque than my 350, but the both ran similar ETs. Why? because HP to the ground was similar. How did I get as much HP to the ground as you did with less torque? By gearing deeper (5.13 vs 6.2) and winding it higher to get the HP with less torque. Also, my engine had "high tech" heads on it, so there may ahve been a technology difference as well.

As a rough general rule, a 454 makes 100 ft lbs of torque more than a 350 at the same HP level. You might see the 454 post 550 ft lbs ad 600 HP, where my small block dynoed 420-440 ft lbs peak torque at 6000ish rpm, and 610 HP at 7000. In equal weight cars, both engines would allow similar ETs and MPH, but the tires, tranny gearing, and rear end gearing would be quite different. Further, as 600 HP small block with 420 ft lbs will out run a 500 HP/500 ft lb big block. This is a common occurrence, because torque is not the measure of acceleration potential, HP is that measure.

Quote "You never mentioned that the technology was different between the PS and the SC motors."

I did not bring up the Pro Stock vs Super Comp comparison, you did. As soon as you put the comparison was on the table, I did indeed point out technology was different between the two engines. Agreed, I didn't mention the bore/stroke ratio, the "top secret" level of development in Pro Stock heads, the twin dominators, etc because I am not the one who brought it up. You brought it up without mentioning any of these things.

Quote:

"My point was that according to you, both had 2 valves and a roller cam, etc so there should be no difference in the power outputs, which of course there is."

I did not put any boundaries on levels of technology, you did. I never said two valves and a roller cam were the overriding technological commonality. My point still stands and has been verified time and again. Given equal technology engines (valves, heads, cam, type of induction, etc) the larger engine will make more power.

I have not forgotten torque, I explained that on page 6 of this thread as well. Torque is just applied force. I can get 300 ft lbs of torque with a big torque wrench at zero rpm, and the HP output is zero as well. It's only as I start to rotate that 300 ft lbs that I start making HP, and the faster I spin the wrench the more effort it takes, and as such the more HP that is made. Torque = force applied, HP = power to do work.

This is also why we worry about torque instead of HP when it comes to the Allison. Force is what will break the converter and slip the clutches. RPM alone (within reason) will not break the tranny. IE, 750 ft lbs at 2000 rpm is more force applied and more stress on the tranny than 500 ft lbs at 3000 rpm.

I have also repeatedly mentioned that torque determines how the vehicle is geared and set-up.

Buddy's turboed V-6s are once again a different level of technology than the 500 CI engines he ran against. Turbo a 500 CI engine and then race Buddy's V-6s.

I guess if I was concerned enough to have a "problem" with your posts it would be this. You misrepresent what I have said, then argue against that misrepresentation. In the world of logic, that is called setting up a "Strawman" then knocking it down. It's either that or you are just not fully reading my posts. However, that small item is way overshadowed by my appreciation that you have not used any negative emotion in this exchange. That is a huge thing to me and much appreciated.

I also said there are two seperate issues here that seem to be getting confused. The first is which is the true measure of power, HP or Torque. The second is why a factory stock DMax outpulls a factory stock 8.1.

Again, the reason a stock DMax outpulls a stock 8.1 is because the 8.1 in a 3500 is not geared as efficiently in factory form as is the DMax in a 2500. As I posted earlier, the 8.1 would need something like a 5.00 ratio to be at it's best. Also, we need to get the trucks the same weight.

Blaine

EWC

09-20-2003, 06:23

Blaine , no my Camaro did not run 10.70 unless I launched @ 5000 RPM . With the single 4 it ran 10.18 @ 136 and the tunnelram ran 10.05 @ 137.40 . The first gear in the Nash was a 3.05 . The MPH readings would indicate a run in the mid 9's . I did have people ask me if I had a small block in the car and I did run it through the traps @ 7600 - 8000 .

My main point was that a lot of the responses were just blanket statements without any results or proof to back them up . You have brought up the issue of weight but have not acknowledged the Trailer Life articule that Tough Guy introduced where the Dmax towed 900 lbs. more and beat the 8.1 from 0-60 MPH by three seconds . In this area the Dmax is the winner , not because the 8.1 is not geared correctly but because the Dmax has more useable torque than the 8.1 . If you were to use the correct gear , as you describe , what kind of MPH would you be able to sustain on the highway with the 8.1 ? If you really want to see a side by side test , get the same gearing in the trucks and run them as I had suggested before . As it is now , the gearing was what Chevy offers and was the best that the 8.1 could get .

I can't help but think that you are trying to use your high RPM theory from your drag car to get a similiar theory set up for the trucks . These are much lower RPM in nature and the HP , I don't feel , is as much of a factor . Torque is the force that moves things , not HP . Another theory is that because the 8.1 doesn't have enough torque to get the RPM's up to use the higher HP , it will not be able to beat the Dmax .

It truely amazes me that there are more excuses for why the 8.1 didn't beat the Dmax than the simple fact that with a 3.73 gear and more torque the Dmax beat the 8.1 . We have covered weight , gearing , HP , torque and more and yet the debate continues . What's next ?

afp

09-20-2003, 20:02

EWC,

I misread your comment about your car. I had not heard the phrase "high 10 teens", and mistook it for "high 10s". I would have called it "low 10s". However, the principals are the same, it just means the direct analogy between out two cars is not as clean as I'd like.

BTW, if I ever build another drag car, it will be a moderate RPM (7200ish) 502-540ish CI Big Chevy with a hydraulic roller, steel rods, a glide, and a 9 inch. It will be in a 2500-2800 lb (max) car/truck. The goal is low 9s and Super Gas capability without having to spend all my frigging time working on the car--as is the case with an 8500 rpm small-block. I also won't be wearing valve springs out in 70 passes, need new rods after 100, won't need funky tranny ratios or an aluminum drum, and won't have to have such odd sized and expensive tires and wheels.

Okay, you said:

"In this area the Dmax is the winner , not because the 8.1 is not geared correctly but because the Dmax has more useable torque than the 8.1."

I disagree. The reason the DMax is the winner in factory form is because it has more useable horsepower, due to being geared more optimally than the 8.1.

You could lock down the rear wheels of your DMax and with a 3000 rpm stall converter, you could put 450ish ft lbs of torque to your rear wheels. However, the HP generated by the rear wheels would be zero. There is still 450 ft lbs of torque being oput to the wheels, but it is not doing anything for you. Now take 300 ft lbs of torque and apply it at 2000 rpm wheel speed and you get 114 HP--114 HP that is working for you and moving you down the road.

The goal is to apply HP to the road. Torque is just the force it takes to generate a given HP at a given RPM. We all get excited about a flat torque curve not because of the torque readings, but becase a flat torque curve allows HP to build rapidly.

The RPM of my drag car has nothing to do with the definition of torque and definition of HP. You call these things "blanket statements", but neither I nor ZF made them up. They are well established principals of measuring force and power, as is the well understood concept (by most) that a larger engine of equal technology will make more power than a smaller one. None of these statements are in dispute.

The proof you ask for is simply to gear both trucks optimally and race them up a hill with the same load. This is a test for power. The mpg the 8.1 will get with a 5.0 gear is irrelevant to it's power output.

Now, if you want to talk efficiency, the the turboed Dmax wins, and that's why I and most of us here bought one.

It appears our disagreement is in how we are defining terms like HP, torque, power, efficiency, equal technology, etc. I imagine that if we were trying to increase the performance of a race car or the efficiency of a tow rig, we'd be doing very similar things--though we'd argue over the meaning of the words..............

Blaine

EWC

09-21-2003, 05:44

The reason I made the statement about the rears being the same was to eliminate any other variable in the tests . Some people totally missed that point . This would mean that the only differences would be the engines and their corresponding power . This would point out that the Dmax has more power , as you say , and would be a clear winner . If this is not acceptable , one would only have to look at the RPM's during the hill climb and then the dyno graphs . I have a feeling the 8.1 would not be at the peak power on the graphs and as you say not at it's peak HP . The Dmax has a lower peak and more torque and that is why it wins . How else do you explain that it runs more MPH with a higher gear ? The 8.1 with more gear can't run that same MPH . That is not HP , that is torque .

The same can be said about your new drag car . Put a big block in , with a lower operating RPM , and you have less maintenance , more torque which allows you to gear accordingly and longer hours of fun .

I hate to say this but , you may have had to much gear and stall in your other car . The 60 ft is way off and this could be from shocking the tires too much at the line . A friend has a street 68 Firebird that has a 400 Pontiac that runs 10.70's . 9 or 10 inch slicks . Not a 455 which is what most think . No tubs either . He is constantly playing with it and has gotten it to run that fast . Last I heard , the rear had a 4.30 gear but that is subject to change at a moments notice as he has 3 other sets .

Drag racing can be a very humbling sport . What you think the car should run and what you get it to run can be very different . With mine being a stick , in a sea of automatics , I had to do things a bit differently . My 60 ft was poor but I did have the HP to cover that . Yes I did say HP . My wheel speed was good and that is one of the reasons that it ran as well as it did . Put a 3.05 first gear in front of a 5.13 rear and then talk about gear multiplication . Most of the cars are geared to peak at a little before the finish line . Mine would not do that . The front end would stay in the air and not drop . It just kept pulling way past the finish line . So according to general theory , I should have had more gear . I couldn't put the power to the ground that I had , so why should I put more gear in ?

It is interesting to note that there are many that put a lot of faith in dynos . They are a good way to test an engines power but are not the end all . Many times you hear of an engine making great power but take it to the track and it just doesn't run . You might not have enough fuel , poor traction , the wrong stall and gear , old slicks , etc . As you have stated the combination is very important . The Dmax might be very efficient at putting its power to the ground or it just might be the torque . The 8.1 had the same trans , with more gear , so that should have been more efficient as you put it .

You still have not made a comment on the Trailer Life articule where the Dmax beat the 8.1 from 0-60 while pulling 900 lbs more weight . I suppose the Dmax made more HP at a lower RPM and that is why it beat the 8.1 ? Or could it be that the flat torque curve allowed it to apply more power over a longer period of time and that built up to a 3 second advantage .

Just as an interesting question , when you talk about combinations and efficiencies , does a rear axle with a 10 inch ring gear make the same power as a rear with a 16 1/2 inch ring gear ?

[ 09-21-2003, 06:23 AM: Message edited by: EWC ]

afp

09-21-2003, 10:42

EWC,

I do not dispute that in factory form, the DMax puts more HP to the ground.

Your comment: "How else do you explain that it [DMax] runs more MPH with a higher gear ? The 8.1 with more gear can't run that same MPH . That is not HP , that is torque."

The Dmax makes it HP at lower rpm, and as such uses the higher gear better than the 8.1. HP is the goal, and torque is what is required to get the HP at the desired RPM.

With the "potential" future drag car, all the increase in force (torque) of the greater displacement does is allow the same power to be made at a lower RPM, which makes things last longer.

Remember my car picked up almost 2 sec going from 5.83 gears to 6.2 gears. With those 6.2 gears, my car was geared close to optimum, when you consider that I was running 14x32s (Hoosiers) that actually measured 15x33--way too big for a small block. My car would quit pulling around 1200ish feet, which is ideal. The problem with the launch was the tires were too tall. I couldn't get the back end of the car level with those tires, even with the four-link all the way down. The launch was very lazy--it wouldn't even lift the front end. Cars with Super Stock chassis and small block typically need to launch hard to run their best.

To fix this I needed shorter tires--like 29x12s, then whatever gear would put the ratio back to where it was. Now with the smaller tires, the car may have liked a slighly taller setting than what it had with the oversize Hoosiers. Regardless, I just ran out of time and money to expeeiment anymore.

The Pontiac has 50 cubes on my engine, and as such would be able to take a taller gear. It is really interesting the different approaches required to make a mall block run vs a big block. You will say this is beacuse of the extra torque of the BB, I'll say it's becasue the BB makes it's HP at a lower rpm, but the end result is the same.

I agree with you on dynos--they are only a starting point. My engine made it's power on the dyno with an 850 Holley and ran okay down the track with it, but it wanted to bog when stalling it against the convertor--it was just too much air. A 750 Holley fixed all that. On the dyno, me engine made peak torque around 6000 and peak HP around 7000, but the best runes were when I launched at 6400 and shifted at 8000, which was well over even the HP peak. I just went with it. At least it was very consistent, and I beat a lot of delay boxes (I didn't have one) who cut better lights but didn't run their number.

I thought I had addressed the Trailer Life article, but I'll do so again. I think it's because the DMax is more optimally geared. I think the DMaxes step up in technology with the turbo is also a factor. When density altitudes become higher, a waste-gated turbo motor will maintain it's advertised power for longer than a naturally aspiriated engine.

With the 16.5 vs the 10 inch, the ratio would be the telling factor. I suppose the 16.5 inch is heavier and and such may have more parasitic losses.

Back to torque. We have gotten very far into exploring opposite sides, and it's probably time to come back a little. I am thinking in terms of sustaining HP. Assuming a flat torque curve, if an engine is making 300 HP and 600 ft lbs at 2625 rpm, if it loses 625 rpm, it loses about 72 HP. If an engine is making 300 ft lbs and 300 HP at 5250 rpm, it can lose 1250 rpm and loses 72 HP. This seems to lend credence to the idea of higher winding engines with flat torque curves at higher rpms. It's probably why the 5.3 (with less torque) I had ran harder than the 5.7 I had--both in ext cab Z-71s. The 5.3 had a 3.73 and the 5.7 had a 3.42. The 5.3 is higher technology, but it was manifest as less torque and more HP at a higher rpm range.

But what if the HP stays the same and the torque decreases as rpm increases? In theory, you'd have an engine that would make the same HP over a broad range and a loss in rpm would not result in a loss in HP. Perhaps this is what is happening when we say and engine is "torquey". In such an engine, you'd want to short shift, where in an engine that has a flat torque curve, you'd want to let it wind.

Blaine