View Full Version : DuraMax really 300hp?? and 520lb torque?
Guys after taking my truck in for several dyno pulls and seeing some others post their results something is starting to bother me. Dont get me wrong I love my truck and the power seems just fine, after all its not a sports car.
But, on the average Duramaxes pull about 240rwhp(rear wheel horse power), and from what I see PSD's pull about 210. Now you do the math, PSD is rated at what? 250hp! The 30 hp between the two at the wheels does not add up, seems like the Dmax is really only making about 280.
Then there is the most important number the torque. 520lb's is what the Dmax is rated at but the dyno results only show about 440 or so, and a PSD pulls about 470!!! How can this be? PSD is rated at less torque.
Just curious if anyone finds that my results are flawed please let me know.
Then there is the most important number the torque.
Horsepower is much more important than torque. Anyone can make a mountain of torque by simply applying more gear reduction. Problem is, gear reduction reduces rpm. Horsepower is torque x rpm, so it reflects the importance of both. Ultimately, horsepower is a measure of how much torque can be made available for a given rpm, or ground speed.
I dissagree, most people on here dont bother thinking about how to generate more torque, rather they want to know what the truck makes.
Besides you are completly off the topic, give me torque lessons at a latter date.
ZFMAX,
Sorry I just read my post and realized that it sounds like I am being kind of a jerk. Just came out that way, didnt mean it too.
cogburne
01-09-2002, 16:41
You have to compare apples to apples. You are not doing that. Take a PSD and a Duramax and mount them in the same chassis, use the same tranny and rear axle and do the dyno. Your numbers would be more realistic then. The Allison eats up alot of torque and horsepower but...It takes much more horsepower and torque to thrash it than a F**D auto.
RWHP, no problem, but I respectfully disagree, my post was both accurate and on topic. You have to understand the relationship between torque and hp to have a meaningful discussion about dyno results, no?
Tader Jack
01-09-2002, 17:08
The real test is out on the road where it counts. There was an article that reported on the Duramax, F--D PS, and D--GE/Cummins in a pulling test with trailers. I can't quite seem to located the url for the article right now, but it told the story quite well. I thing it might have been Trailer Life or one of those camping magazines.
That made me a believer and convinced me to purchase a Dmax over the PSD.
If anyone has the url for the article let us all know.
Jack Schultz, McKean, PA
jackschultz@adelphia.net
http://photos.yahoo.com/bc/jack_schultz2001
2001 Chevy Silverado, 4-WD, 2500HD, Crew Cab, Short Box
LT Trim, Black Onyx w/ Tan Leather
------------------------------------------------
Beltronics 980 Radar Detector
Keep in mind that we have the mother of all automatic transmissions- The Allison. It takes 60 hp to turn the tranny. Other makes with different trannies take less HP away from the rear wheels. The 6 speed should have more RWHP. I haven't heard what that number is? So, you sacrifice HP for the features of the tranny.
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2001 Chevy 2500HD 4x4 D/A LS Regular Cab Una-Goose Hitch, Line-X, Westin CP/SS Nerf Bars, Lucerix Mirrors. Took delivery 12/8/00. Virginia DURAMAX plates.
The real test is out on the road where it counts
Exactly. And the reason the Duramax can out pull the PSD is that it has more horsepower. Not a whole lot more, as RWHP points out, but more nonetheless, and horsepower is what matters, not engine torque. That's what I was getting at in my post, but I guess I wasn't clear.
arveetek
01-09-2002, 17:46
ZFMax,
I have always been taught that torque is more important than horsepower, because torque is what moves the vehicle, and hp is how fast it moves.
There are lots of engines that have enormous hp, but little torque. These are typically high-rpm motors. Diesels tend to have high torque, because they are lower-rpm motors.
Can you explain to me why hp is more important than torque?
Thanks.
Casey
I have always been taught that torque is more important than horsepower, because torque is what moves the vehicle, and hp is how fast it moves.
You're right, torque is what moves the vehicle, and more is better. Torque is rotational force. 1 ft/lb of torque is 1 lb of force applied at a 1 foot radius.
But you're wrong, hp is not how fast it moves. RPM is how fast it moves.
These two things, torque and rpm, are interrelated and both are equally important. Gear reduction multiplies torque but divides rpm. So when you gear something down, you have more torque at the output, but you slow down. This is what happens when you downshift. Likewise, you gear something up and you lose torque at the output but you gain speed.
Obviously, downshifting to get more torque to the rear wheels is not the most desireable solution, since it slows you down. What you really want is as much torque as possible to the rear wheels for a given ground speed. So instead of torque or rpm, you need a metric that reflects both. That's what horsepower is. It's literally torque x rpm (divided by 5252, but that's a nit). Horsepower describes the combination of how much torque you're making and how fast you're making it. You can make less torque with one engine than another, but if you make it faster it allows you to apply more gear reduction and go the same speed, and that gear reduction multiplies the torque. It's the combination of torque and rpm that matters, and that's the definition of horsepower.
In a nutshell, the engine with the most horsepower will put MORE TORQUE to the rear wheels for a given ground speed, because horsepower reflects both torque and rpm.
So how can a PSD out-torque a Duramax on the dyno and yet have less power?
Well, that's because the dyno is showing engine torque as measured at the rear wheels, not rear wheel torque. Read my post here, I think it'll clear up a lot of this:
http://www.62-65-dieselpage.com/ubb/Forum3/HTML/002094.html
[This message has been edited by ZFMax (edited 01-09-2002).]
Dragsled
01-09-2002, 19:16
The mfg states the hp and torque values in accordance with a very specific set of conditions given in the SAE standard. It is also measured at the flywheel so the rating is independent of the vehicle. That is why chassis dynos do not repeat the mfgs numbers.
The mfgs us the corrected horsepower and torque standard SAE J1349. SAE J1349 specifies the brake horsepower and torque be corrected to 29.23" mercury barometric pressure, 77
Does the PS have a longer stroke then the Dmax? The Dmax is "over square" isn't it?
In a nut shell (not all encompassing):
For "pulling" you want TORQUE, example, "Big Trucks", tractors, etc., relatively low HP compared to torque. Long stroke, low RPM's
For cruising (racing) around on the Blvd.s you want HP, example; motorcycles, sports cars. High HP relatively low torque. Short stroke, high RPM's.
NorCalDMAX
01-09-2002, 21:33
Man O Man,
All this HP/Torque is making me real anxiuos to go out and Race my car...
I must say...Numbers are for Ph'd's and statisticians.....because the projected potential is more fun to debate then actually do.
It all matters if goes and does what you want it to do..
Hey here is some numbers for all you number crunching people.....at 4800 rpm with 11 lbs boost my little ol SBC makes appx 851ft lb tq and 780HP, hit 6800rpm and 12.9 boost, It makes 1081ft lbs tq and 1311 hp ...Bring on them PSD's...HAHAHAHAHAHAHAHA I got some stump pulling power for them......Hey I wonder if an Allison would work in my car and be legal for the class. Kind of neat to have a tranny think for me while I am going down the track...1 less thing for to me do..... http://www.62-65-dieselpage.com/ubb/biggrin.gif...What do you think Big Al.......
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2001 Chevrolet K3500 4x4 LS
Duramax/Allison
Crew Cab
Long Bed
Victory Red
Light Grey Leather with Bench front
G80 Rearend
E-mail: cii@onebox.com
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The powerstroke has a longer stroke than the Dmax, but- it has a smaller bore.
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2002 3500 Duramax/ZF6 speed/4x4
LS Interior
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REAL men drive trucks....
REAL trucks are diesels....
www.picturetrail.com/gallery/view?username=dslpowr (http://www.picturetrail.com/gallery/view?username=dslpowr)
NorCalDmax,
How does that blown SBC pull a 6% grade with a 10,000 load? Think it will do it for 200,000 miles http://www.62-65-dieselpage.com/ubb/wink.gif
Like you said, all that matters is it goes and does what you want it to.
When was the last time anyone drove/raced a dyno graph?
Lone Eagle
01-09-2002, 23:14
Very interesting reading! I bought my DMAX to out pull the competion with my 5th wheel on the long steep hills here in the Rockies. At least on paper this engine make 500+ ft. lbs. from 1500 to 3000 RPMs. That should keep a smile on my face from April through Oct. Later! Lone Eagle
Allot of people get hung up on dyno numbers, and will immediately declare a winner on who produces highest dyno numbers. Unfortunately those dyno numbers only state what peak power was produced, they tell you nothing about application performance. Dyno numbers are just that..... numbers. Now looking at dyno horsepower and torque curves tells you much more about the application power output then just peak dyno numbers. What exactly is this dyno number? Well it's the "peak" production of horsepower and or torque. Key word is peak. This peak number doesn't tell you squat about the rest of the rpm range before peak and after peak. When accelerating, that peak moment only lasts a very short time when considering the entire rpm range. That means if your not at peak your somewhere else in the rpm range. You'll spend far greater time when driving towing at other than your "peak". That's why the rest of the rpm range is so important.
Your can have an application that produces more peak power than another, but just because it produces more peak power doesn't necessarily mean that's it's the best performer.
Torque is force performed. A unit of measure for force is Torque. Horsepower is a derivative of torque. Horsepower is basically torque over time. The more horsepower the greater amount of torque is available over a wider range.
Application A is 300hp/550tq compared to application B 300hp/600tq. Application is A is more efficient in using it's torque cause its at or closer to it's peak throughout more of the rpm range than application B. Application B produces more peak but is only at or close to peak for a shorter amount of time in the rpm range when compared to A.
Again, horsepower is derived from torque. Horsepower and Torque are both your friends. Horsepower just give you another perspective on how the torque curve your application behaves. Little horsepower means your application isn't at or close to it's torque peak for long through the rpm range. Lots of horsepower means your application is at or closer to it's torque peak for a longer period throughout the rpm range.
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Derek M
02 Chevy 2500HD D/A CC LB
95 Z28 11.077@132.120
88 Mustang LX
http://home.attbi.com/~z28sc
[This message has been edited by Derek M (edited 01-10-2002).]
How does rotational mass fit into the picture, such as adding wieght to the flywheel - will that increase torque ?
Why does a Cat or Cummins in heavy equipment produce gobs of torque and very little HP in comparison ? rough numbers - 1200 ft.lbs of torque and only 275 hp.
On a dirt bike I had, I added a flywheel weight to increase the torque (or so I thought) to facilitate trail riding.
Any thoughts on my comments ?
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PROUD AMERICAN If you don't LOVE this country - LEAVE
2001 2500HD LS Ext.Cab,short bed,D-max,Allison, Onyx black w/graphite int.Leer 700 hard tonneau,16X8 Eagle Alloys w/265-75-16 Coopers, Powerplay from Kennedy diesel
1988 K1500 shortbed stepside Paxton supercharged 4" Trailmaster lift w/33" tires
2001 Polaris Sportsman 500 HO
77TransAm
01-10-2002, 07:33
Here's a link to one of the more interesting (and in-depth) descriptions of the hp/torque relationship I've read. Taking time to read it may help answer some of the questions in this thread (but not the one about how much hp/torque the DMax really makes...sorry http://www.62-65-dieselpage.com/ubb/smile.gif )
http://www.zhome.com/ZCMnL/tech/torqueHP.htm
For "pulling" you want TORQUE, example, "Big Trucks", tractors, etc., relatively low HP compared to torque. Long stroke, low RPM's
For cruising (racing) around on the Blvd.s you want HP, example; motorcycles, sports cars. High HP relatively low torque. Short
stroke, high RPM's.
Torque is twisting force. 1000 ft/lbs of torque is literally 1000 lbs of force at a 1 foot radius from your hub. Torque at the wheel accelerates the vehicle, per f=ma. Doesn't matter whether it's a truck or a sports car. Torque at the wheel is what matters.
But the problem with looking at torque is that it only tells half the story. Torque without considering the RPM it's made at is totally meaningless.
For example, I have a 1/2hp hand held electric drill motor that turns 1000rpm. Therefore, at 1000rpm, it's making 2.626 ft/lbs of torque (torque = (hp * 5252)/rpm)
Say I put a gear on it's chuck that has 10 teeth. And I mesh it with another gear that has 10,000 teeth. And I hold the drill motor on. What happens to the 10000 tooth gear?
Since the drill motor is making 2.626 ft/lbs of torque, and it's geared at a 1000 ratio (10,000/10), the big gear will have 2,626 ft/lbs of torque!
Wow, that's 5 times as much torque as a Duramax. Why don't they just put 1/2hp electric drill motors in our trucks and gear them like this instead?
The answer is that although the gear reduction increased torque by a factor of 1000, it also decreased rpm by a factor of 1000. The big gear is only turning 1 rpm. Yeah, you can pull a trailer, but not very fast.
This illustrates why torque without rpm is so meaningless. To make it meaningful, we have make that torque at a suitable rpm. This is why horsepower was invented. It's literally defined as torque times rpm. It considers both, and recognizes that they're equally important.
Just like with the drill example, torque at the wheel of your truck varies depending on the gear you're in. Because of this, manufacturer's (and dynos) don't show torque at the wheel. They show it at the engine. And torque at the engine is not what moves the truck, torque at the wheel is what moves the truck. Because horsepower considers the rpm as well as the torque, it alone describes how much torque will be available at the rear wheels for a given ground speed. And that's what matters.
So I disagree. When looking at the specs, the horsepower is what matters for towing performance. Assuming it's geared properly, the truck with the most horsepower is going to get the trailer to the top of the hill first, not the truck with the most torque. This isn't my opinion, it's a fact of physics.
[This message has been edited by ZFMax (edited 01-10-2002).]
When looking at the specs, the horsepower is what matters.
Ahhhh,
Probably why all manufacturers quote horsepower numbers first when spec'ing and engine.
Ask an experienced big truck mechanic what size engine is in a particular truck. He will either quote the cubic inches or horspower or both with torque secondary.
The Duramax is said to have 300/520. Don't the rear wheel numbers roughly confirm that when d/t loss is taken into account?
Maybe the Ford drivetrain is much easier to turn thus less d/t loss. Is that good or is that an indication of drivetrain strength? Heavier components absorb more power.
It's also difficult to compare engines as cogburne said....
You have to compare apples to apples. You are not doing that. Take a PSD and a Duramax and mount them in the same chassis, use the same tranny and rear axle and do the dyno. Your numbers would be more realistic then. The Allison eats up alot of torque and horsepower but...It takes much more horsepower and torque to thrash it than a F**D auto. when there are so many differences in the trucks themselves.
The bottom line is how they perform in real world usage.
One thing that bothers me is the implied higher power of the Dmax but in real world towing, there are conflicting results as to the Dmax's ability to outpull the 250hp PSD on a long steep hill. Anybody have an explanation?
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
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1994 K1500 Blazer 350 Loaded, Flowmaster duals
NorCalDMAX,
There is a tranny for you (S9600 - 1250 nhp input), but the "box" weighs in at nearly a ton!!! All that weight won't help your "rocket" much!
P.S. They're used in big, Off-Highway haul trucks (150 Ton Payload)! Anybody wanna try to haul 150 tons with their HD??!?!?!?
http://www.62-65-dieselpage.com/ubb/wink.gif
Chevy Ryan
01-10-2002, 10:45
Just wanted to clear up the bore and stroke issue.
Duramax: 4.06 x 3.90
Power Stroke: 4.11 x 4.18
Cummins: 4.02 x 4.72
Long stroke equals lots of torque. That's why the Cummins can make 660 lb-ft (non-pickup applications) with only 5.9 liters.
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Ryan
2001 Chevy 2500HD 4x4 6.0L
Percentage wise, it's not that great a difference. 84% efficient for the Dorf and 80% for the Duramax. I can live with the 4% difference as my 'max was very noticeably quicker when I compared it to the PSD before I bought. The noise difference alone is worth the 4% to me.
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John Brunsgaard-jeb
01 Silverado LT SB CC D/A 4x4 2500HD
ZF,
Your "practical" explanation of torque is irrelevant in this case (even though it true from the physics stand point as you go on to say). 3.55, 3.73, 4.10 gear ranges are much closer to one another then your example of a 10 tooth compared to a 10,000 tooth sprocket.
My point is; for pulling heavy loads over long distances you want an engine that produces torque down low. (fuel&longevity) This why KW's, Pete's, JD's, IH's, etc... don't run formula one engines in them just because they make a lot of HP. Useless HP in these applications, unless you run one of those 10,000 gear sprockets some where in the transmission.
I personally can't imagine working ground all day turning 14,000 RPM's. I know it would use a lot of fuel and I'm thinking that the TBO would be about 5hrs verses 4,000+ hrs??
Sorry little off topic but: I use to fly an airplane (T-34C) with a Pratt & Whitney PT6, that made 550 shp and 1315 ft/lbs at 33,000 RPM. It went through the fuel like crazy! This engine would be all but useless in a truck because of it torque curve; nature of turbines.
Your "practical" explanation of torque is irrelevant in this case (even though it true from the physics stand point as you go on to say). 3.55, 3.73, 4.10 gear ranges are much closer to one another then your example of a 10 tooth compared to a 10,000 tooth sprocket.
Well, I disagree, I think it's completely relevant. Yes, it was an extreme example, but sometimes extreme examples are useful to illustrate a point. The point is that torque can be easily created with gearing, and torque by itself means absolutely nothing because it has no time component. You have to consider the speed at which the torque is made to have a meaningful number, and when you do that, you're working with a number we call horsepower.
My point is; for pulling heavy loads over long distances you want an engine that produces torque down low. (fuel&longevity)
"torque down low" associates a torque figure with an rpm, no? You've added a time component. Now you've made torque meaningful.
The torque and rpm of an engine together create this thing we refer to as "horsepower". Their relationship is:
horsepower = (torque x rpm) / 5252
When we have situation like towing a big load down the highway at a given speed, there's a certain amount of horsepower required from the engine to make that happen. The horsepower at the engine is made up of some combination of torque and rpm, but whatever the combination, it follows this formula. We use gearing to transform that torque/rpm combination into some other torque /rpm combination at the rear axle, and it will still follow this formula. So if we have 300hp at the motor we'll have 300hp at the axle, although it may be structured as 3000rpm/520ft-lbs at the engine and 804rpm/1940ft-lbs at the axle (if we're in 4th gear on an Allison). Both are 300hp.
We can get to that desired mix at the rear axle with a high rpm/low torque engine (applying more gear reduction), or we can get there with a low rpm/high torque engine (applying less gear reduction). Yes, us diesel fans choose the low rpm/high torque motor because lower engine rpm causes less frictional losses and less wear. So I absolutely agree with your statement.
But we don't choose the low rpm/high torque configuration because it out-pulls a high rpm/low torque engine. When geared properly, whichever engine has the most horsepower (i.e. combination of torque and rpm) will out pull the other one. Every single time. That was my point.
Torque is not "more important" than horsepower as some seem to believe, torque is a component of horsepower, the other being rpm. Both torque and rpm are equally important, and if you want to know which engine will get the trailer to the top of the hill first, look at the combination of the two: horsepower.
Sorry little off topic but: I use to fly an airplane (T-34C) with a Pratt & Whitney PT6, that made 550 shp and 1315 ft/lbs at
33,000 RPM.
I'm not familiar with "shp", but 1315ft/lbs of torque at 33,000rpm is 8,262hp.
This engine would be all but useless in a truck because of it torque curve; nature of turbines.
With that kind of horsepower it would tow a trailer like gangbusters. It would require a whole bunch of gear reduction of course.
[This message has been edited by ZFMax (edited 01-11-2002).]
shp= shaft horse power
It didn't make 8,000+hp
Please explain the math formulas for HP/Torque. Can you explain why the hp and torque pass one another at less than 5252RPM
Breck,
Seems the 5252 thing might true with any gas engine....
A quick look at a dyno pull from my car with supercharger, low and behold the HP/TQ cross at 5252 rpm.
http://home.attbi.com/~z28sc/dyno/dyno9-556.jpg
Why's it different? Dunno... The type of combustion? Ingnition versus Compression combustion?
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Derek M
02 Chevy 2500HD D/A CC LB
95 Z28 11.077@132.120
88 Mustang LX
http://home.attbi.com/~z28sc
[This message has been edited by Derek M (edited 01-12-2002).]
a64pilot
01-12-2002, 20:15
I know this is a truck forum, but I believe I can explain why your formulas may not have worked for the PT6 (airplane Engine).
It's possible that the torque is measured at propeller RPM, something less than 2500 I would guess. The 33,000 or whatever the RPM was is probably the turbine output shaft RPM.
I will say that this string is interesting, just waaaay above my head.
http://www.theunholytrinity.org/cracks_smileys/otn/funny/moon.gif
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2001 C3500 LT Charcoal Grey
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No, this formula is a fundamental relationship that applies to any rotating power source. It's derived from the basic definition of a horsepower: the ability to do 33,000 ft/lbs of work in one minute. Some fella named "Watt" a long time ago figured out that's how much work a horse can do in a minute.
If you take a shaft that's spinning 5252rpm, a point at a 1 foot radius from that shaft will travel 33,000 feet in a minute's time. If it also has a force of 1lb, now you have 33,000ft/lbs in that minute, which is the definition of a horsepower. So that's where the 5252 comes from. It's literally 33,000 divided by the circumference of a circle that has a 1 foot radius (33,000 / (2*pi))
If you take your actual torque and multiply it by your actual rpm, and then divide it by this special rpm where 1 ft/lb = 1hp, you get your actual horsepower. Essentially, you're scaling the result to meet the definition of what some horse could do a long time ago. Conceptually, it's convenient to think of horsepower as just (torque * rpm), i.e. the combination of the two.
So it has nothing to do with the engine type, it applies equally to handheld electric drills and steam locomotives and the rear axle on our trucks.
If someone ever hands you a dyno sheet where torque & hp aren't the same at 5252rpm, and both sides are scaled the same, something is wrong.
I dove into all this because some folks seemed to think that torque is somehow a better metric of towing performance than horsepower. It's not. It's actually just a component of horsepower. Typically, when we say a motor has a lot of torque, really what we're saying is that it makes it's horsepower (the parameter that matters) without having to turn a whole lot of rpm. That reduces frictional losses and wear. But a motor with more horsepower and less torque, like the 8.1, will out tow us any day of the week, let's not kid ourselves. I say that as devout diesel fan, too, I've had only diesel pickups for 10 years now. But it's a simple fact of physics.
[This message has been edited by ZFMax (edited 01-12-2002).]
As stated in earlier posts, the HP and torque MUSt cross at 5252. It is simple math.
IF the Dmax could be revved that high, the numbers would cross.
From what I've seen, the HP and torque peak at the same RPM on the 2002's. I've seen 520ish down where it is claimed to peak rising to 580's at 2800ish. The 2001's seem to peak a few hundred RPM sooner and a bit less on torque.
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John Kennedy
www.kennedydiesel.com (http://www.kennedydiesel.com)
John@kennedydiesel.com
2002 Chev. K2500HD Dmax/Allison Crew Cab Long Bed Pewter/Tan LT Driving it!!!
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hunter98
01-12-2002, 22:43
Torque is a figure that is a function of horsepower. An engine with 800 ft lbs at 2200 RPM's will produce twice the horsepower than an engine that produces 400 ft lbs. That 800 ft lb engine if it produced 800 ft lbs at 1100 RPM's would give it half the amount of horsepower at that RPM of 1100. Generally speaking, torque is wonderful, in the since that the more of it you have, the more horsepower you have. The difference that we have with our duramax compared to the 496, is that at 1400 RPM's the durmax may have 500 ft lbs of torque, while the 496 may have only 300 foot lbs. Hence we yave 2/3 more horsepower at 1400 rpms to cruise down the road.
It is as simple or as complex as you want it to be.
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
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MNBowTie
01-12-2002, 23:33
Hunter98,
You are mostly correct in the relation ship between the dmax and the 8100. However, you are assuming the same gears 3.73's. Now lets set the 8100 up with the available 4.10 gears and now we have a closer comparison and on level ground. I bet 0-60 with a 10,000 behind, would be neck and neck, or I would put a small wager on the 8100 getting to 60 first. I remember reading an article from Trailer Life Magazine with identical trucks and trailers except one was a dmax and the other a 8100 with 4.10 gears. They did some around town driving,as well as a 6 percent grade and a 7 percent grade. In the 6 percent grade the 8100 had pedal left and toped the hill 3-4 mph faster than the dmax with the pedal to the metal. However, the dmax shined on the 7 percent grade by holding it's speed where the 8100 loss speed. I wish to heck I would have printed this article. It wasn't an all out test between the two trucks just kind of first looks report from about a year ago. My 2 cents worth.
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<UL TYPE=SQUARE> 2500,Silverado LS,Carmine,D/A,CC,SB on order TPW Mid. Feb. !!FOR SALE 98,GMC, 7.4,4.10 lckr, auto, CC,LB, 62xx,5/75GM war. $19,000[/list]
Maverick
01-13-2002, 00:44
I have raced a 2500HD CC SB 8.1/Allison up hill with my 3500 D/A up here in Alaska. We were both pulling close to 5500#. I had a very slight edge pulling against him. I beat him though.
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01' Chevy Silverado/ Reg. Cab LS 3500 4x4/ Duramax Diesel-Allison/ Aluma Flatbed Body/ Curt Gooseneck Hitch/ Lucerix Mirrors/ Amsoil Air Filter/ 9' Sno-Way Snow Plow/ High Idle Installed/ Lund SS Screen Front
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ZFMax,
Good post. The history lesson was enligtening. I think I'll save that one. http://www.62-65-dieselpage.com/ubb/wink.gif
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
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Posted by ZFMAX
I dove into all this because some folks seemed to think that torque is somehow a better metric of towing performance than horsepower. It's not. It's actually just a component of horsepower.
I would think it would be the other way around, since torque is actually measurable force/work, and horsepower is calculated or derived from torque therefore horsepower would be a component of torque. If it
I can't say which is more important for everyone, but for my truck, I would take torque over horsepower. My Porsche can make 240 hp and go 150 mph, but I wouldn't ask it to haul my boat out of the water on a steep ramp.
Here's some informtion I pulled/ torqued/twisted off the internet:
Horsepower and torque are related measurements of engine output in practical terms, an engines horsepower rating (hp) is most relevant to how well the engine performs at high speed, while it
MNBowTie
01-13-2002, 14:30
Not that I want to end this thread, but the simplistic way to interpret all of the above math is to evaluate the combined hp and torque IE Dmax= 820, 8100= 795. Seems to me that would be the easy way to measure a workhorse.
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<UL TYPE=SQUARE> 2500,Silverado LS,Carmine,D/A,CC,SB on order TPW Mid. Feb. !!FOR SALE 98,GMC, 3500, 4x4 SW,7.4,4:10,lckr, auto, CC,LB, 62xxx,5/75 GM war. $19,000[/list]http://www.picturetrail.com/gallery/view?p=999&gid=570842&uid=46235 (http://www.picturetrail.com/gallery/view?p=999&gid=570842&uid=462385)
Well, I see a number of people still don't get it.
the simplistic way to interpret all of the above math is to evaluate the combined hp and torque
Yeah, that would be simplistic, but unfortunately it would be wrong.
Torque is a component of horsepower. The other component is rpm. In other words, multiply torque by rpm to get horsepower. You can't evaluate a truck by combining a component of the horsepower with the horsepower, that makes no sense at all. That's like evaluating a drink by combining the tequila with the margarita. Combine the tequila with the lime juice instead.
My Porsche can make 240 hp and go 150 mph, but I wouldn't ask it to haul my boat out of the water on a steep ramp.
Remember the golden rule, hp = (torque * rpm) / 5252
Geared for a 50rpm rear wheel speed, 240hp will generate 25,210 ft/lbs of torque at the rear wheels: 240 = (25210 * 50) / 5252
By comparison, a 225hp PSD geared for a 50rpm rear wheel speed will generate 23,634 ft/lbs of torque at the rear wheels: 225 = (23,634 * 50) / 5252
A 300hp Duramax geared for 50rpm will generate 31,512 ft/lbs of torque at the rear wheels: 300 = (31,512 * 50) / 5252
A 340hp 8.1 geared for 50rpm will generate 35,714 ft/lbs of torque at the rear wheels: 340 = (35,714 * 50) / 5252
Noticing a pattern? Assuming it's geared for it, the motor with the most HORSEPOWER is capable of putting the most torque to the rear wheels at a given ground speed. Regardless of the peak torque of the motor.
Your Porsche's motor has less torque than a 225hp PSD, yet with enough gear reduction, your motor is capable of putting more torque to the rear wheels at the same speed. Why? Because it has more horsepower. What it lacks in torque, it more than makes up for in rpm. Therefore, you can apply more gear reduction (which multiplies torque) and voila, you end up with MORE torque for a given speed where it really matters, at the rear wheels.
horsepower is calculated or derived from torque therefore horsepower would be a component of torque
Hmm, if green is derived from blue and yellow, does that make it a component of blue?
No, that means blue and yellow are components of green. Mix them together and you get green.
Mix torque and rpm and you get horsepower. Same thing. Torque and rpm are the components. Horsepower is the result.
Anyhoo, I'm just about out of analogies and examples to explain the concept of torque, rpm, and hp, but I'll give it one more shot ... I'll make this real world ...
Let's say we're towing down the highway with our Duramax. The conditions are:
2045rpm engine speed
our Allison is in overdrive (.71)
we have the stock 3.73 rear axle ratio
772rpm rear wheel speed (2045rpm / .71od / 3.73 axle)
stock 245/75R16 tires
70 miles per hour (30.46" tires * pi * 772rpm * 60 / 12 / 5280)
Let's say we're pulling a load that requires 1000ft/lbs of torque at the axle to hold this speed
What's happening here?
The motor is generating 147hp. It's making this in the form of 2045rpm and 378ft/lbs of torque (it's not making 520 because we're not at full throttle). 147hp = (378 * 2045) / 5252
The gearing is converting this 378ft/lbs & 2045rpm makeup of 147hp at the engine into a 1000ft/lbs & 772rpm makeup of 147hp at the axle: 147hp = (1000 * 772) / 5252. The gearing isn't adding or subtracting horsepower, it's just changing it's torque/rpm makeup. It's increasing the torque and decreasing the rpm. The torque goes up by the same amount that the rpm goes down. The amount is the total gear reduction, which in this case is .71 * 3.73 = 2.65. Divide the engine's rpm by 2.65 to get the wheel's rpm: 772 = 2045 / 2.65. Multiply the engine's torque by 2.65 to get the wheel's torque: 1000 = 378 * 2.65.
Okay, now say we come to a hill. To hold our 70mph (772rpm at the axle) we now need 1940 ft/lbs of torque at the axle, in other words, almost twice as much. 772rpm & 1940ft/lbs comes out to 285hp: 285hp = (1940 * 772) / 5252
We floor it. The torque at the motor jumps from 378ft/lbs up to 520ft/lbs. That's all she has. For the moment anyway she's still turning 2045rpm, so we've got 202hp available: 202hp = (520 * 2045) / 5252
But 520ft/lbs at the motor times the gearing (.71 * 3.73) is only 1377 ft/lbs at the rear wheels. That's not enough! The truck will start slowing down if we don't do something quick!
So we downshift to 4th. The transmission is now 1:1. What happens?
Well, assuming the rear wheels are still turning 772rpm, the motor is now turning 2880rpm: 2880rpm / 1:1 / 3.73 = 772rpm.
We still need 1940 ft/lbs at the rear wheels to hold this speed. With a 3.73 axle and a 1:1 transmission, this means we now need 520ft/lbs at the engine: 520 = 1940 / 1:1 / 3.73. Fortunately, the Duramax has this much available at 2880rpm so we continue right up the hill at 70mph.
Notice that we don't have any more torque at 2880 rpm than we have at 2045rpm, but we can climb the hill at 2880rpm and we can't climb it at 2045rpm.
Why? Because we have more horsepower at 2880rpm. The torque hasn't gone up, but the rpm has, and therefore we can apply more gear reduction and that multiplies torque that the rear wheels have. We raised the rear wheel's torque without raising the engine's torque.
What if the hill was steeper? What if, instead of requiring 1940ft/lbs of torque at the rear wheels to hold 70, it required, say 2245ft/lbs to hold 70?
In this gear, we now need 602 ft/lbs of torque from the engine: 602 = 2245 / 1:1 / 3.73. Our Duramax can't provide that even at full throttle.
We have to drop down another gear. 3rd on the Allison has a 1.41 ratio. At 772rpm rear axle speed, that would put our poor Duramax at 4060 rpm: 4060 = 772 * 3.73 * 1.41. Well above it's rev limit. We'll have to slow down to the 3200rpm limit, which puts our speed at 55mph.
Since we're not trying to go 70 anymore, it won't take as much torque at the rear axle to hold this load. It'll take about 55/70th's of 2245, or 1764ft/lbs. With this gearing, 1764ft/lbs at the rear wheels is only 335ft/lbs at the engine: 335 = 1764 / 3.73 / 1.41. The Duramax can easily provide this at 3200rpm at a little over half throttle.
It wouldn't matter what we had for an axle or gearbox. A 772rpm rear wheel speed and 2245ft/lbs of torque is 330hp. Try all you want, but you will not find a torque & rpm combination of the Duramax that can be geared into 772rpm & 2245ft/lbs of torque. It can't be done, even if you put in 4.10's or 4.56's or a ZF or a CVT or whatever, because the motor doesn't have 330hp. Not without a power box anyway.
BUT, if we had an 8.1, it's easy. Leave your 3.73 in there, put the Allison in third gear. 4060rpm is no problem and the 8.1 can make the required 427ft/lbs of torque there: 427 = 2245 / 3.73 / 1.41. In other words, that 427ft/lbs of torque will be 2245ft/lbs of torque after we multiply it by the 1.41 3rd gear ratio and 3.73 axle ratio. This is because the 8.1 can make 330hp and the Duramax can't.
So the 8.1 is going to motor right up the hill at 70 while our Duramax goes 55. Even if we had perfect gearing for the hill, we couldn't go 70. We could get closer, but we couldn't go 70.
In a nutshell, horsepower wins every time, because it describes which vehicle can put the most torque to the rear wheels for a given ground speed. And that's what pulls the freight.
[This message has been edited by ZFMax (edited 01-13-2002).]
Lone Eagle
01-13-2002, 21:11
NWBowTie, There were two good articles on the DMAX/8.1. I have the first one here on my desk. It is the Oct.2000 issue. Both trucks were towing 10,400 lbs. The times are listed below. I have the second article. I just have to find it. Later! Lone Eagle
Demax 8.1
0 to 60 solo 9.5 9.0
0 to 60 towing 24.4 30.3
40 to 60 towing 13.0 16.4
hunter98
01-13-2002, 22:43
When buying a new Farm tractor, which spends most of its time pulling at close to full load. We look at and buy Horsepower. One tractor size produces 375 Horsepower at 2000 RPM's and 410 HP at 1800 RPM's, while the other tractor produces 325 Horsepower, and 350 at 1800 RPM's. It isn't the torque but the horsepower that we are paying six figures for. The reason that the horsepower increases from 2000 to 1800 RPM's is that the peak torque is lower than 2000 and increases at a faster rate than the RPMs decrease. Providing more horsepower to do the work. And yes these engines are all rated at over 1000 ft lbs of torque. MORE LOW END TORQUE = MORE LOW END HORSEPOWER!
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
That's the way I recall it, the 8.1 will out accelerate the DMax, towing is another story. As we all know the most difficult scenario for a gasser is when it tows up a hill and the RPMs drop from the HP sweet zone. The DMax's torque maintains hill climbing speeds while using more a fuel efficient torque sweet zone at lower RPMs.
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'01 Silverado 2500HD Dmax/Allison EC 4x4 SB, Westin Bars, Fumoto Valve
"Assuming it's geared properly, the truck with the most horsepower is going to get the trailer to the top of the hill first, not the truck with the most torque. This isn't my opinion, it's a fact of physics."
Boy, now I'm really confused. Let's see, the Duramax outpulled the 8.1 with a load of 10,500 lbs. So, the 8.1 must not be geared properly???
Anyway, it looks like you need that torque to increase that rpm to get that horsepower going, but once you get moving, the horsepower takes over provided there's enough of it to keep the rpm up, and if there isn't, the torque has to increase the rpm again through a gear change, so that the horsepower can take over again. (Sounds like handoff from a fullback to a halfback...) Anyway, pulling my boat up a steep ramp slightly above idle does it for me. I like that torque...
I need a beer...
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BBugg
No, more horsepower = better acceleration as well. The vehicle with the most average horsepower over it's operating range will accelerate the best.
I can't account for one set of anectdotal results.
I'm just repeating myself. I'm going to stop now. This is pure physics. I haven't given one single opinion.
Hunter98 has it exactly right.
slapshot44
01-14-2002, 01:33
ZFMax,
I've been following this post and I applaud your patience. You've done a great job taking a complicated physics problem (work) and explaining it in layman's terms. I sure wish I had you for a study partner when I took my dynamics course. At this point, I think you might want to defer to Kennedy's quote in his signature. http://www.62-65-dieselpage.com/ubb/wink.gif
redneckcowdoctor
01-14-2002, 05:55
ZFMax
According to my dusty old college physic textbook your right on. None of my professors ever presented the subject as clear and concise as you did--congrats.
As for as the 8.1 not being geared right: It might not be a case of right or wrong gearing but that the available transmissions favor the power curve of the Duramax over that of the 8.1.
Wow, thanks guys. It's good to know someone was following all that drivel!
So, was the original question answered?
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'93 GMC SLE 6.5TD Banks Power Pack D/A Sle XC/LB 4WD TPW 01-01-02 GOA NRA EAA AOPA AMA VFW Good Sam Cessna 180
hunter98
01-14-2002, 18:26
I hope that you all understand now! Rear end gearing is wonderful at allowing you a tall enough gear to run more efficiently, or to have a low enough rear end (4.10.4.56) to get a load started in first gear, or to have enough power at highway speed to be able to tow the load. I.E. A truck with a 4.10 rear end traveling at 2200 RPM's will have more horsepower available than the truck with 3.73 at 2000 rpms. With the Duramax's power curve that is virtually flat at 500-520 ft-lbs, that 10% more RPM's equates to 10% more horsepower available at max throttle at that RPM to move the load.
My truck contraversially enough runs about 4 mph faster at the quarter mile with my 33" tires, than with the 30.5" tires that were factory. This is attributed to the fact that the truck is now geared better to take advantage of the power band. It shifted to 5th before at too low of a speed to take advanage of all the power.
If you gave the 8100 a 10 or 13 speed, it would work great as a grain truck. But who wants to spend all day cruising around at 4000 to 5000 RPM's.
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
I was always tought in simplest terms HP is the measure of the rate at which work is done. If nothing moves then no HP has been applied. Torque is a twisting force that can be applied and have nothing move.
Both numbers are very important for pulling loads up a hill. HP is how fast it can pull it up the hill and torque is how much it can pull it up a hill. If you have three engines with 300 HP and one has 520 TQ, one has 600TQ and one has 700TQ. Loaded the one with the most torque will pull the hill fastest. Now if you have three engines with 520 TQ one has 300 HP, one has 240 HP and one has 200HP. The 300 hp engine will pull it fastest.
Not to long ago Ford, Dodge and Chevy Diesels made around 180 HP and around 450 TQ. My big block gasser made 235HP and just shy of 400TQ. With 10,000 pounds of trailer I could climb 6% grades on the east coast faster than the diesels could. Now with the New much higher HP diesels and some more torque they can out climb that truck.
I know my duramax will out climb my last gasser. Better yet it will get better mpg. But it has more HP and more Torque. The older diesels with more torque but less hp could not.
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2001 Chevy LT C3500 Crew Cab Dually, Duramax, Allison,pulling 12500 pound Holiday Rambler Alumilite.
If you have three engines with 300 HP and one has 520 TQ, one has 600TQ and one has 700TQ. Loaded the one with the most torque will pull the hill fastest.
I'm curious as to why you believe this?
Doesn't 300hp, after gear reduction to any given rear wheel speed, ALWAYS translate into the same amount of torque at the wheel? Regardless of the torque at the engine?
Let's just see ...
with 300hp & 520ft/lbs of torque, how much rpm are we turning? rpm = (hp * 5252) / torque:
(300hp * 5252) / 520ftlbs = 3030rpm
How much gear reduction do we need to turn 3030rpm into 772rpm at the rear wheels (70mph)? gear reduction = input rpm / output rpm
3030rpm / 772rpm = 3.925:1 gear reduction needed
If we apply 3.925:1 gear reduction to 520ft/lbs of torque, how much torque will we get at the rear wheels? output torque = input torque * gear reduction
520ftlbs * 3.925 = 2041ft/lbs of torque at the rear wheels
Now let's repeat those steps for 300hp & 600ft/lbs of torque:
(300hp * 5252) / 600ftlbs = 2626rpm
2626rpm / 772rpm = 3.401:1 gear reduction needed
600ftlbs * 3.401 = 2041ft/lbs of torque at the rear wheels
Hmm, came out the same. Maybe 300hp & 700ft/lbs of torque:
(300hp * 5252) / 700ftlbs = 2251rpm
2251rpm / 772rpm = 2.916:1 gear reduction needed
700ftlbs * 2.916 = 2041ft/lbs of torque at the rear wheels
Hmm. All 3 combinations put 2041ft/lbs of torque to the rear axle at 70mph.
The first thing they teach you in physics class is that force = mass * acceleration. As long as the force and the mass are the same, the acceleration should be the same, right? So why do you think one of these will out-accelerate the others?
I think whoever taught you had it wrong.
Let go of this notion that the combination of torque and hp is what matters for towing performance. Torque is a component of horsepower. The ONLY thing implied by a high combination of the two that the motor is turning less rpm, because horsepower is torque * rpm. You're not saying it can accelerate or climb a hill faster. Only the combination of torque (force) and rpm (rate of application) describes that property (assuming you're geared correctly). And the combination of torque and rpm is called Horsepower.
[This message has been edited by ZFMax (edited 01-15-2002).]
ZFMax, I applaud you for your tenaciousness and your concise and accurate explanations. But not matter how hard you try, some of us will never get it. At some point in time you must use Slpashot44's suggestion. "I think you might want to defer to Kennedy's quote in his signature." Jim
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2001 SILVERADO /2500HD EXT CAB /LWB/ DURAMAX / ALLISON / 4X4 / LT / HUSKY MUD FLAPS /
FIRESTONE AIR BAGS/
MNBowTie
01-15-2002, 13:16
ZFMax,
Now, that was a fantastic explanation and see that easy math doesn't apply when trying to figure what's going to do the job better.
Now, I'm going to have to crunch some numbers to figure out how much weight my buddy was pulling on about a 7% grade with his F**d PSD and walked right by 7.4L 4:10 gasser and a V10 stuper duty. The gassers were both holding to metal about 35-40 mph and the PSD was able to pass at about 50 mph. It might be that both the gassers were over 60K on miles and the PSD was new. Thanks again for spending the time in your reply, Wow! http://www.62-65-dieselpage.com/ubb/cool.gif
ZFMax,
http://www.plauder-smilies.com/nosmile/claps.gif http://www.plauder-smilies.com/nosmile/claps.gif
Now would you mind explaining http://www.plauder-smilies.com/nosmile/atom.gif cold fusion http://www.plauder-smilies.com/nosmile/atom.gif , my 5th grade son had to write a 1 page report on it last week because everyone in the class was talking in the hall. No kidding - Catholic school. http://www.62-65-dieselpage.com/ubb/wink.gif
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mdrag
========================
'01 3500 "BIG DOOLEY" DMAX/ALLISON PICTURES (http://www.picturetrail.com/gallery/view?username=mdrag)<UL TYPE=SQUARE>
<LI>2001 3500 LT Crew Cab/LB7 DMAX 6600/M74 Allison 1000 Series/4x4 G80/Light Pewter/Tan Leather
<LI>12 Disc CD Changer/Escalade Steering Wheel Audio Controls/Pioneer TS-C1653 Component Speakers
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[/list]
This is for all of us who are "wrong". I spoke with James Watt last night and he never heard of a D/A... "Torque Rules"
Check out this website out if you haven't had enough:
http://www.boston-bmwcca.org/bimmer/1999/03/horsepower-and-torque.html
Here's a sample:
The Case For Torque
First of all, torque rules, from a driver's perspective. Any given car, in any given gear, will accelerate at a rate that exactly matches its torque curve, allowing for increased air and rolling resistance as speeds climb. Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear. Yet, if you start plugging figures into that formula, you can see that the horsepower would double at 4000 rpm, with the same level of acceleration. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the horsepower and torque numbers only get friendly at 5252 rpm, where they always come out the same.
In contrast to a torque curve (and the matching push back into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.
You don't believe all this?
Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? OK. Now that we're all on the same wavelength (and I hope you didn't get a ticket or anything), we can go on.
The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?
Because (to quote a friend), "It's better to make torque at high rpm than at low rpm, because you can take advantage of gearing".
For an extreme example of this, I'll leave car land for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a long time ago down in Sturbridge, MA), rotating lazily on a shaft which was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drive wheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice.
On the other hand, twelve rpm of the drive wheels is around one mile per hour for the average car, and, in order to go faster, we'd need to gear it up. If you remember your junior high school physics and the topic of simple machines, you'll remember that to gear something up or down gives you linear increases in speed with linear decreases in force, or vice versa. To get to 60 miles per hour would require gearing the output from the wheel up by 60 times, enough so that it would be effectively making a little over 43 foot pounds of torque at the output (one sixtieth of the wheel's direct torque), which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60.
Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us: 6 horsepower.
OOPS. Now we see the rest of the story. While it's clearly true that the water wheel can exert a bunch of force, its power (ability to do work over time) is severely limited.
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BBugg
Guys, you're very kind, and I appreciate your comments. And I know, I should not keep doing this. But at the same time, should we let misinformation be posted here and go unchallenged?
Like that drivel in the first part of bbugg's post ...
Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it.
This is true, BUT, it fails to consider the fact that you're going two different speeds at the torque & hp peaks.
For a given ground speed, however, you'll accelerate harder if you've geared the vehicle to be at it's horsepower peak instead of at it's torque peak. That's a fact. I'll refrain from giving examples, but if anyone followed my other examples it'll be obvious. Why do you think the transmission downshifts when we floor it?
Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300
foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear.
Same deception is at work in that statement. If you're making the same torque at twice the rpm, that means you can apply twice as much gear reduction and still be going the same speed. And then you'll have TWICE as much torque at the rear axle and you'll acclerate TWICE as hard!
Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker?
That's a poorly designed experiment that proves nothing. Do it this way instead. Take it to it's torque peak in TOP gear. Punch it. Now, slow back down to the speed where you punched it, and downshift to a gear that puts the engine at it's horsepower peak instead. Punch it. It'll be noticeably stronger. That's why we downshift and wind up our motors when we climb hills. Horsepower wins every time, because for a given ground speed, it describes how much torque can be sent to the rear wheels.
Still don't believe me? Get two trucks with ZF's going side by side, each at 2000rpm. Have one guy romp on it, and have the other guy downshift and THEN romp on it. Who do you think will accelerate the hardest?
Bottom line, if you're going to compare acceleration at the horsepower peak versus the torque peak, you have to equalize the speeds where the comparison is made, otherwise it's an invalid comparison.
Okay, I'm done. Really. People can post all the misinformation they want, I won't react. If you believe me, need any swampland in Florida?
[This message has been edited by ZFMax (edited 01-15-2002).]
hunter98
01-15-2002, 16:59
An experiment for all Duramax owners that are 2002 or have had the Cruise control update. Set the cruise at 70 MPH which is about 2000 RPMs, just over the peak torque, and floor it. Ok, see how she responds at that RPM without downshifting. Click the CC off now and try it again and FEEL the POWER!
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
ZFMax,
I did not say out accelerate. I said climb the hill at a faster rate of speed.
Every physics class I have had stated HP is the rate at which work can been done, that means how fast. Torque is the twisting force available. You can apply torque an not move anything. If nothing moves you have not used any HP.
As for the statement about the 454(7.4L) and 4.10 gears. Not the right set up, only rated for 10,000 pounds. The 454 needs the 4.56 gear. Then it will run in the hills with most stock diesels, prior to the 2001's. I know my 96 Crew Cab dooly with the 454 and 4.56 gears pulling 12,000 pounds would run a way from my friends 97 quad cab dodge cummins 4.10 and an 10,500 pound RV on the saluda grade. Now with my crew cab dooly duramax and 3.73 gears I can climb the saluda grade 4 mph faster than I could with the 96, that means 58mph. Not bad, but I want to pull 12,000 over it at 70mph.
------------------
2001 Chevy LT C3500 Crew Cab Dually, Duramax, Allison,pulling 12500 pound Holiday Rambler Alumilite.
Okay Dave, I'm confused.
Loaded the one with the most torque will pull the hill fastest.
Every physics class I have had stated HP is the rate at which work can been done, that means how fast
These two statements contradict each other. Which is it? (hint: your understanding of hp is incomplete)
Anyway, I showed that all 3 of the 300hp motors you described (520, 600, and 700ft/lbs of torque) put the EXACT same torque to the rear wheels at 70mph. The torque at the engine is irrelevant.
If they all have the exact same combination of torque and rpm at the rear wheels, why do you think they'll climb a hill at different speeds?
Isn't it the forces acting on the rear wheels that matters? Why does the specific combination of torque/rpm at the engine matter at all for towing performance?
Didn't we use gearing to convert the engine's combination of torque/rpm into the combination we need at the rear wheels? And didn't 300hp always come out the same, no matter what it's makeup at the motor?
I did not say out accelerate. I said climb the hill at a faster rate of speed.
Doesn't torque available at the rear wheels determine how fast something can go? As well as it's acceleration?
If I have a moving object, and a force of 2000lbs resisting it, won't it accelerate if I apply more than 2000lbs of force and decelerate if I apply less than 2000lbs of force? And if I apply more than 2000lbs, won't it accelerate until the force resisting it matches the force I'm applying? Thereby ending up at a higher speed?
So I repeat my question. At 70mph, all 3 of the 300hp motors (520, 600, 700 ft/lbs) put the SAME force to the rear wheels. Why do you think they can climb at different speeds?
[This message has been edited by ZFMax (edited 01-16-2002).]
Fuzzy math, remember that term from the presidential election?
ZFMax...so what.
"Anyway, I showed that all 3 of the 300hp motors you described (520, 600, and 700ft/lbs of torque) put the EXACT same torque to the rear wheels at 70mph. The torque at the engine is irrelevant"
Yes you did but you changed the gear reduction ratio in all of your examples.
My truck does not have an adjustable rearend. Does yours?, is there a switch I have not found that lets you switch gear reduction in the rear end?
So use your numbers again keeping the same gear reduction but different torque input. My calculator says that the output tourqe will change.
But then again....so what. I will never buy an arguement that says you if keep HP the same and increase torque and you will have no increase in real world driving/towing performance.
------------------
2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
More Power
01-16-2002, 12:36
Power = work/time
That's why The Diesel Page compares the Ford/Dodge/GM trucks on a 6% grade with the same trailer. "Work" is pulling a 10K trailer a measured mile up a 6% grade. "Time" is the elapsed time it took to get from point A to point B (mile marker to mile marker).
Results - an off-the-shelf Duramax "truck" always produces the most "power".
MP
Yes you did but you changed the gear reduction ratio in all of your examples.
Well, if you have 3 different engine rpms, and you want all 3 trucks to run the same speed, you pretty much have to change the gear reduction, no?
My truck does not have an adjustable rearend. Does yours?, is there a switch I have not found that lets you switch gear
reduction in the rear end?
No, not that I know of. But they provide a different way to change gear reduction, this thing called a "transmission". There's this big lever coming out of the floor with 6 forward speeds and a reverse. It's described in the owner's manual. There's a couple different types you can get.
So use your numbers again keeping the same gear reduction but different torque input. My calculator says that the output tourqe will change.
What does your calculator say about the output rpm?
300hp = 520ft/lbs of torque @ 3030rpm
520ft/lbs * 3.925 gear reduction = 2041ft/lbs torque at the rear wheels
3030rpm / 3.925 gear reduction = 772rpm rear wheel speed (70mph)
300hp = 600ft/lbs of torque @ 2626rpm
600ft/lbs * 3.925 gear reduction = 2355ft/lbs torque at the rear wheels
2626rpm / 3.925 gear reduction = 669rpm rear wheel speed (60.66mph)
300hp = 700ft/lbs of torque @ 2251rpm
700ft/lbs * 3.925 gear reduction = 2748ft/lbs torque at the rear wheels
2251rpm / 3.925 gear reduction = 574rpm rear wheel speed (52mph)
Sure enough, if we raise torque at the motor, and keep the hp and gearing the same, we raise torque at the rear wheels. No argument.
But now you're going slower. Hmm.
You could've accomplished the same thing by just downshifting. For example, if I have the 520ft-lb/3030rpm engine, and I just downshifted to a gear that gives me 5.284 of total gear reduction instead of 3.925:
300hp = 520ft/lbs of torque @ 3030rpm
520ft/lbs * 5.284 gear reduction = 2748ft/lbs torque at the rear wheels
3030rpm / 5.284 gear reduction = 574rpm rear wheel speed (52mph)
What's the difference between this and the 700ft-lbs/2251rpm combination geared at 3.925:1?
Tell me again why a high torque/low rpm combination of 300hp will outperform a low torque/high rpm combination of 300hp?
Bottom line, there's no free lunch here. Torque and rpm are equally important. Your argument ignores rpm.
I will never buy an arguement that says you if keep HP the same and increase torque and you will have no increase in real world driving/towing performance.
Funny thing about the laws of physics, whether or not we believe them doesn't change them a bit.
I'm a big fan of diesel pickups. I got my first one 10 years ago. I will never own another gas powered pickup. The combination of towing power and fuel efficiency and longevity is worth the extra money to me. But, I don't kid myself into thinking that my 300hp is somehow stronger than someone else's 300hp just because mine is made of higher torque at a lower rpm. That'd be silly.
[This message has been edited by ZFMax (edited 01-16-2002).]
Allison Jettester
01-16-2002, 14:27
ZFMax'
I took physics in college, too. That's why I am a mechanical engineer. We all know that it's the throttle that makes it go up the hill! http://www.62-65-dieselpage.com/ubb/rolleyes.gif You have a lot of patience! but you are correct. Jet engines have a lot of torgue, too, but it just makes the airplane roll http://www.62-65-dieselpage.com/ubb/smile.gif Force = Mass X Acceleration and Horsepower is Force over Time--torgue doesn't even enter the equation. It is used on a dyno to calculate horsepower by spinning wheels on a load cell. In an airplane we measure force directly by pulling on the load cell. Well, that's my $.02 worth.
Joe
[This message has been edited by Allison Jettester (edited 01-16-2002).]
Thanks, Joe. I also are an in gan ear (if that wasn't obvious by my obsession with such mundane matters)
The real problem here is that too many people have it stuck in their heads that torque is some separate property that you can have in addition to horsepower, rather than looking at it as a component of horsepower. But old notions die hard. Sigh.
[This message has been edited by ZFMax (edited 01-16-2002).]
ZFMax.
"Sure enough, if we raise torque at the motor, and keep the hp and gearing the same, we raise torque at the rear wheels. No argument.
But now you're going slower. Hmm."
Kinda sounds like the reason low end torque is useful in a diesel engine. You gain pulling power at a lower RPM. Fuel efficiency is a benefit. With more power at a lower RPM (and speed in your simplistic augument) I can do one other thing, Speed up. Hmm. By doing that I still have more power at the wheels.
And given a one sided simple viewpoint the laws of phyics apply. Apply multiple inputs and you have the real world.
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2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
Kinda sounds like the reason low end torque is useful in a diesel engine. You gain pulling power at a lower RPM. Fuel efficiency is a benefit.
Yep! But that's a separate metric than pulling a trailer up a hill.
With more power at a lower RPM (and speed in your simplistic augument) I can do one other thing, Speed up.
Do you mean by just applying more throttle and raising rpm?
Keep in mind that the basis of our debate is that all these different motor configurations make 300hp. They're just making it with different combinations of torque & rpm.
If you raise rpm, and horsepower stays at 300hp, then torque has to go down.
Hmm. By doing that I still have more power at the wheels.
I thought we agreed that all of these configurations have 300hp?
Go back and check every single pair of torque & rpm figures in those examples, whether they're at the engine or at the wheels. They're all 300hp. hp = (torque * rpm) / 5252
Are you saying you have some way to take 300hp at the engine and have more than 300hp at the rear wheels? And the way to do this is to make the 300hp with higher torque and lower rpm?
Show me.
And given a one sided simple viewpoint the laws of phyics apply. Apply multiple inputs and you have the real world.
I hate to break this to you, but the laws of physics describe the real world. That's what the whole field is about, understanding the real world and the rules that govern it. If you think I missed an input, please let me know which one it is.
I really think you've got it stuck in your head that torque is something you can have in addition to horsepower. I don't know why you're so married to that concept. It's wrong, and as long as you cling to it, you'll continue trying to rationalize that somehow the physics isn't real world.
Torque is a component of horsepower. The other component is rpm. A high torque version of X horsepower means low rpm, nothing more. A low torque version of X horsepower means high rpm, nothing more. Once you gear them for the same rpm, you'll have the same torque. That's not an opinion, and it's not leaving out an input, and it's as real world as anything gets.
[This message has been edited by ZFMax (edited 01-16-2002).]
cantravel
01-16-2002, 18:43
ZFMax: How I wish you had been my physics teacher back in high school. Instead of struggling for an MBA, I might have accomplished a PHD in mechanical engineering.
Your analysis and the examples you utilized, have clarified this question for me.
Now I know my Duramax diesel is a better choice to power my truck than 300 horses. And no poop to clean up either!
Thank you for sharing your knowledge.
01 Chev K3500 D/A LT Crew LBx
Diesel page member #40
ZFMAX,
Lets hope you are self employed, because you are spending way too much time at work teaching physics.
Everyone else,
The funny thing is that we are still stuck with the main question does the DMAX make the power claimed.
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2001 Silverado
3500CrewCab, 4x4, Duramax/Allison
Towing a 40' Enclosed Exiss 2 car race trailer.
ZFMax,
One more try and I'll let it end, for the good of all mankind.
Trust me here I KNOW torque is a component of horsepower. That is why you can't say:
"All of this really points out why it's truly horsepower that matters, not engine torque." It is a component after all right?
It's important to remember the dyno measures torque and rpm and then from these calculates horsepower. On the dyno it takes more water flow to the water brake to increase the load on the engine being tested. As the test engine's torque rises more water flow is needed. As the test engine's torque drops less water flow is needed. The dyno's water brake does not respond to horsepower. Major adjustments to water flow are needed as an engine crosses its torque peak but none are needed as it crosses its horsepower peak. In other words the water flow to the brake during a dyno test follows the engines torque curve and not its horsepower curve. Torque is what twists the tire, prop, or pump. Horsepower helps us understand an amount or quantity of torque. (Torque + time)
At or below 5252 rpm any engine's torque will always be higher than its horsepower, and above 5252 rpm any engine's horsepower will always be higher than its torque.
Why because they are a component of each other.
One more point (I promise RWHP)!!
Horsepower can be converted into other units as well. For example, 1 horsepower is equivalent to 746 watts or 2,545 BTU (British thermal units) per hour. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts. If you took that 746 watts and ran it through an electric heater, it would produce 2,545 BTU in an hour (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F). One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, the horse would burn 641 Calories in one hour doing its work if it were 100-percent efficient. So if horsepower is the be all end all, I will burn 192300 calories driving my truck for one hour. I'm hungry and tired.
Mark
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2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
Sigh. To teach something, the other person has to actually want to understand. This is a waste of time.
Oh well, it's nice to know all this 'splaining was helpful to some. Thanks. I'm done.
I have read about all I can get my hands on concerning this subject and I have not read one document outside this forum that does not state that torque determines acceleration. I even spoke with a couple buddies that race funny cars and they put torque over horsepower. These guys will be at the Winter Nationals and that ain't no drivel. Actually, contrary to one fella, I see no drivel here.
Lexus puts out an engine that has variable valve timing eliminating the usual compromise between low-end torque and high-rpm horsepower Why not just more horsepower??
When I selected a cam for my Harley, I picked a high torque cam, cause I like to be quick off the line. Should I get my money back from Crane??
Because people do not agree, does not mean they do not want to understand, and be careful, because it goes both ways.
In any case, there has been a lot of thought and work put into these two pages and I've enjoyed reading everything.
I will have to admit that I demonstrated this torque/horsepower thing to my girlfriend and she preferred horsepower... so there, I'm wrong!!
Anyway, I've pasted one last article just to bore everyone. If you think it says horsepower is more important, you might want to stop here...
"The terms horsepower and torque can be confusing at times. One of the top authoritative magazines on engines, Hot Rod Magazine, took twenty pages to explain torque vs. HP. Here's a paraphrase of what they said.
Simply defined, horsepower is the rate of doing work over a given amount of time. According to experts from SAE, one horsepower (1 HP) equals 550 ft-lb. per second or 33,000 ft-lb. per minute. Another familiar formula is the one which states RPM x Torque / 5252 = horsepower
Torque is the measurement of the strength of the rotational movement and determines how fast a car, boat, or airplane accelerates up to a required speed.
An example here should be helpful:
Think of a V-8 car engine that puts out approximately 300 HP or more at 6,000 rpm compared to a large diesel semi-truck that puts out 300 HP at 2,200 rpm. They are both 300 HP engines; however, they are very different and offer different performance capabilities. The V-8 car engine puts out 300 HP and produces 263 ft-lb. torque at its top working speed of 6,000 rpm. The diesel truck engine puts out 300 HP but puts out 716 ft-lb. torque at its top working speed of 2,200 rpm.
If you put the V-8 car engine into a diesel truck (even though it is also 300 HP) it can not even move the truck. This is because the low speed strength (TORQUE) of the V-8 is not sufficient to even get started. The diesel engine has much higher torque but is very large in size and weight, i.e. 700 - 900 cubic inches and 2500 lb. in weight. And obviously, you could not put a diesel engine in a car because it is too big and heavy."
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BBugg
Mr. ZFMax, could you please step off the soap box. My 21 years in school AND my job teaching, (I think) show a desire to learn.
The components of horsepower are force, distance and time. Distance and time are self-explanatory but force, specifically a twisting force, is what torque is all about. Torque is stated as foot-pounds and represents how much twisting force is at work
As you may have noticed, this measurement of torque does not include time. One-hundred foot-pounds of torque is always 100 foot-pounds torque, whether it is applied for five seconds or five years. So, if you want a quick answer to the difference between horsepower and torque, just keep in mind that horsepower involves the amount of work done in a given time, while torque is simply a measurement of force and is thus a component of horsepower.
So now we have a technical understanding of how torque interacts with horsepower, but let's move beyond that to some real-world examples. For instance, we all know that a car moves from a dead stop in 1st or low gear, yet as the car's speed increases, the gears must be moved up through 2nd, 3rd and 4th to maintain acceleration. This is because at low speeds the transmission's gears work to transmit maximum torque from the engine to the wheels. (ahhhh the torque of a diesel) You want this because it takes more force, or torque, to move a vehicle that is at rest than it does to move a vehicle in motion (by the way ZFMax, that
Of course torque determines acceleration.
Torque at the rear wheels!
And torque at the rear wheels will be at it's peak, for a given ground speed, when the motor is at it's horsepower peak. I proved that. Several times!
If you put the V-8 car engine into a diesel truck (even though it is also 300 HP) it can not even move the truck. This is because the low speed strength (TORQUE) of the V-8 is not sufficient to even get started.
You still don't understand the concept of gear reduction, do you? Because the V8 is making it's 300hp at 6000rpm instead of 2200rpm, you can apply almost three times as much gear reduction to it for a given speed. This multiplies it's lower torque into the same torque. Look at the examples above.
If you still insist that you can accelerate hardest from a given speed at your torque peak, or if you insist that you can pull a trailer up a hill best at your torque peak, go right ahead. Just stay in the right lane, okay? Because I'm going to downshift, put my engine at it's horsepower peak, and go around you. Every time.
Y'all have closed your minds. As Marks comments about gearing clearly demonstrate, you don't understand the role of gearing. But I've explained it every way I can think of.
[This message has been edited by ZFMax (edited 01-17-2002).]
"And torque at the rear wheels will be at it's peak, for a given ground speed, when the motor is at it's horsepower peak. I proved that. Several times!"
How and when did you prove that?
I have seen about numerous post on dyno results that have (Rear Wheel)Max HP of around 250 @ 2900 RPM. Max Torque is around 475 ft lbs @ 2600 rpm. Torque drops off after that.
How and when did you prove that?
Read the examples. It's all there.
I have seen about numerous post on dyno results that have (Rear Wheel)Max HP of around 250 @ 2900 RPM. Max Torque is around 475 ft lbs @ 2600 rpm.
As I explained before, those dyno charts are showing engine torque as measured at the rear wheels, not rear wheel torque. There's a big difference. Engine torque does not reflect the multiplication you get with the gear reduction offered by the transmission and rear axle. If you only had 475 ft/lbs at your rear wheels, the truck couldn't get out of it's own way.
hunter98
01-17-2002, 09:10
I want to be done TOO!, Torque shows how much HP is produced at a given RPM. More Torque means more HP, and that is why Torque is important. If an engine produced 650 Ft. Lbs at 1400 RPMs, and 450 Ft. Lbs at 2000 RPMs, compared to an engine like the Duramax that produces roughly 520 at both points, give me the 520. With the 650 at 1400 RPMS the important HP number is 173, at the 2000 and 450 ft lbs it would be 171. Hmmm, now with this engine the RPM's increased, but the HP didn't, now with the Duramax, at 1400 RPM's, would produce 139 HP, and at 2000 RPM's would produce 198 HP, hmmm, the HP increased this time. I would rather have the ability to have increasing and the Higher HP, than the higher torque. I will bet any one of you that whether your 650 ft lb engine was at 1400 or 2000 RPM's, I would pass you in my Duramax at 2000 RPM's!, Now you say that your 650 can be made at 2000 RPM's, well you now produce 247.5 HP, which is why you could now pass me.
Higher Torque is a function of when the engine makes its HP, a diesel is a High Torque engine, and inherently produces its HORSEPOWER at lower RPM's than a gas engine.
DO I WANT MORE TORQUE, A RESOUNDING YES, BUT I WANT MORE TORQUE BECAUSE IT WOULD GIVE ME MORE LOW END HORSEPOWER, without sacrificing the high end!
If you don't get it by now, go back to my moms class in fourth grade, maybee she can explain it better! http://www.62-65-dieselpage.com/ubb/wink.gif
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
Let's put this one to bed with PullinPower's test in the Industry News Forum!!
ZF is talking about the rear dif here. 3.73:1 makes for a significant torque increase.
------------------
Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter, Straight Piped PIC (http://uscom.com/~hoot/cars/duramax/gmc/exhaust/jvn03.jpg)
PS2K Propane, 22 Gal. LP Tank PIC (http://onramp.uscom.com/~hoot/cars/duramax/gmc/propane/bigtank1.jpg)
Allison Deep Pan, Transynd Syn ATF PIC (http://uscom.com/~hoot/cars/duramax/gmc/allison/allis10.jpg)
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level PIC (http://uscom.com/~hoot/cars/duramax/gmc/allison/allis11.jpg)
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Kennedy Headlight Booster Kit TRUCK PICTURES CLICK HERE (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
Mark, work out how much torque you'll get to the rear wheels at the torque peak you provided, 475ft/lbs @ 2600rpm (235hp). Do it at any speed you want, it doesn't matter if it's 1mph or 1000mph.
Now, using the exact same ground speed, work out how much torque you'll have at the rear wheels at the horsepower peak instead, 250hp @ 2900rpm (452ft/lbs).
If you don't know how to do this, I'll show you. Or look in my previous example of the 3 300hp engines.
Tell me which one puts more torque to the rear axle for a given speed, running at the horsepower peak or running at the torque peak?
Think of any other example of different horsepowers and torques you want to give, I don't care. Pick 400hp & 100ft/lbs of torque compared to 300hp and 1000ft/lbs of torque. Which is capable of putting the most torque to the rear wheels at ANY given speed? Mark? Bbugg?
Torque is made in an engine through the combination of combustion pressure and stroke (stroke is mechanical advantage on the crank).
But what you're missing is that there's another way to make torque, too. We can gear something down. The more rpm we start with, the more we can gear it down, and the more torque we can put at the rear wheels. So rpm is *really* important. In fact, it's just as important as the torque we start with. This is what you guys aren't getting.
Hmm, if *only* we had a number that combines both torque and rpm into one number http://www.62-65-dieselpage.com/ubb/wink.gif
That would be ideal, because it would truly tell us how much torque we could put to the rear wheels for any given speed.
Doggone it, where could we get such a number? I guess we could multiply torque and rpm, that would give us a combination of both. What do you think? You think that would do a better job of telling us how much torque we can produce after gear reduction than just engine torque or rpm alone?
Let's do it! One more thing, though, to make the number more meaningful, can we divide it by 5252 as well? That'll scale it down to where it approximates how much torque a horse can generate at it's normal speed. And then we can name it after the horse. Any ideas for a name? Hmm, something that represents horse, and power, let me see ...
[This message has been edited by ZFMax (edited 01-17-2002).]
arveetek
01-17-2002, 14:28
Wow! This has been extremely interesting, and just a little bit over my head!
ZF, if I understand you correctly, about the only other thing that could affect performance between various 300hp vehicles with different torques, after the rear axle that is, would be tire size and vehicle weight, correct? That would be a couple of variables that could change things.
If your three 300hp with different torque engines puts the same torque to the wheels thru the transmission and rear axle, but one has larger tires which decreases the torque, and that vehicle also weighs more, meaning more mass to move, then it would be at a disadvantage to an otherwise equal truck, right?
Just trying to see if I'm following this correctly.
Excellent and very perceptive comment!
Torque is defined as ft/lbs ... which means the number of pounds of force at a 1 foot radius from the center of the hub.
If you have say, 2000ft/lbs of torque at the rear wheels, and you had tires that were exactly 2 feet high (i.e. a 1 foot radius), then the tire will exert 2000lbs of forward force onto the pavement.
But, our tires are closer to two and a half feet high. This is functionally equivalent to applying less gear reduction. In other words, because the radius is more than 1 foot, we go a little farther every revolution but we have a little less torque.
How much does that decrease the force applied to the ground? The simplest way to figure this out is to just scale it with the ratio of the difference in size. So just take 30" / 24" = 1.25, which means a 30" tire is 25% taller geared than a 24" tire. Therefore 2000 ft/lbs of torque will be 2000 / 1.25 = 1600lbs of force where the rubber meets the road on a 30" tire. Likewise, if a given rpm gives us 70mph with a 24" tire, it'll give us 70 * 1.25 = 87.5mph with a 30" tire. So it did the exact same thing as applying less gear reduction.
Rule 1 in physics is force = mass * acceleration, or more commonly, f=ma. Acceleration then is a=f/m. If you know the force on the rear tires, and the mass of the vehicle (which has a constant relationship to weight on earth), you can literally figure out the acceleration. So yes, weight is a major factor in acceleration, no question.
There are a whole bunch of other factors at work, too, a truly accurate calculation isn't this simple, this is just close. The biggest one has got to be "area under the curve". Essentially all these examples have been at specific data points, i.e. "X" hp, "Y" torque, "Z" rpm gives you this. But in the real world, most of us don't have continuously variable transmissions. So you have to "integrate" and find the area under the curve for the range of rpm that we operate over. That integrated horsepower is more meaningful than peak horsepower.
And then there are even more factors. For example, rotating inertia (i.e. a big flywheel) goes up with the square of the radius, so it has a bigger effect than static inertia. Essentially, it stores some of our power, which means that it'll rob some away while we're accelerating, which makes us accelerate slower. This whole thing is the subject of debate with dyno guys, whether a brake dyno or an inertia dyno gives a more true representation of torque and power. Other forces skew the results, too, like wind resistance.
I love your question. It shows you've thought it through.
I took 4 semesters of physics. Hard courses, and I never really liked it that much. But it's handy for understanding things like this.
[This message has been edited by ZFMax (edited 01-17-2002).]
Let me get this straight, my old 6.0 Liter Vortec had 300 HP too. If I had only changed the gearing from in it from 4.10 to 3.73 I could have improved my performance to that of the Duramax AND saved $40,000.
Wow I am dumb after all.......
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2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
arveetek
01-17-2002, 20:43
MA,
I'm still not sure that I'm following this correctly, but, if what ZF has said is true, then you may be partially correct. If in fact the 6.0L engine was 300hp, you could in fact change the rear axle to make it pull equal to the Duramax. However, since the 6.0L creates its power in a higher RPM band, you would have to LOWER the ratio to do so. In other words, you would have to go from a 4.10 to a 4.56, or something even lower, I'm not a math guy, so somebody else figure it out. Geared properly, the 6.0L could pull the same load at the same speed. However, it would be way up there in RPM's where the HP is in order to accomplish this, thus, wearing the engine out quickly, sucking the fuel, being very inefficient, etc.
That's why the Duramax is still a better choice. Not necessarily because it simply has more torque, but because it can produce more power at a lower RPM = HP. That way you can tow the same load up the same hill at the same speed but at a lower rpm, using less fuel, being much more effecient, even though both motors have the same HP. I think I'm starting to understand this!
Basically, you're both right. Torque without HP is meaningless, but a higher torque motor can move a load better because it can do so more effeciently....am I close on this?
ZF,
Your remark on the heavy flywheel reminded me of an old fashioned gas engine that my Grandfather and I own.....it's a 1905 vintage International 2HP "hit and miss" engine. It has two, huge flywheels on it. It only fires every one in a while, when it slows down to the point that the governor allows the exhaust valve to close and allow the combustion process to take place. It just sits there and spins for the longest time purely on inertia. It was used to run a water pump back in the old days. This thing probably cranks out a lot of torque, but very little HP, simply because it can't accelerate worth a darn.
Very interesting stuff.
MABurns,
I believe that your old 6.0l gasser would perform as well as a Duramax, as long as you can keep it up around 5000RPMs http://www.62-65-dieselpage.com/ubb/wink.gif
Kevin
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<UL TYPE=SQUARE>
<LI>2k Dodge 3500 CTD, auto, SLT+, Quadcab
<LI>DD2 injectors, Power Edge COMP fueling/timing box, DTT tranny upgrades, 4" exhaust, K&N, Line-X liner, Reese 15k hitch
[/list]
Mark, you're getting there, you went the wrong way on that gearing, but you're getting the idea.
If you accept that hp = (torque * rpm) / 5252, and if you accept that gear reduction divides rpm and multiplies torque, and you know how to multiply and divide, the answer to your question is within your grasp:
1) Pick a target speed. Doesn't matter what it is. It's easier if you just use rear wheel rpm as the units, but you can convert that to mph if you want.
2) Pick an engine hp, torque, and rpm. It can be anything, just make sure it's legal. It MUST follow the formula hp = (torque * rpm) / 5252.
3) Divide the engine rpm by the desired rear wheel rpm to get the needed gear reduction to go that speed. Gear reduction does divide rpm, right?
4) Multiply the engine torque by that amount of gear reduction to get the torque you'll have at the rear wheels. Gear reduction does multiply torque, right?
Now just repeat steps 2 through 4 for ANY other engine hp/torque/rpm combination. Or even another hp/torque/rpm point on the same motor, doesn't matter. As many times as you want. Just make sure your target speed stays the same and your combination of hp/torque/rpm are legal. Otherwise it's an invalid comparison.
Look at the results.
Show me one example where a motor with less horsepower than another motor ended up with more torque at the rear wheels, at the same rear wheel speed. Just one, and you win the debate.
Do you not believe that rear wheel torque determines how fast you can go, or accelerate, with a given load?
Or do you believe that somehow this process is flawed?
There is nothing even remotely fuzzy about this math. It's just working with the basic relationship of torque, rpm, and horsepower, and the effect of gearing. It couldn't be simpler. And it's dead nuts right.
I fully realize this is a non-intuitive concept to you, the idea that extra rpm can be turned into more torque. But it's true.
I certainly didn't buy my 300hp Duramax because I think somehow my 300hp is stronger than another 300hp, just because mine is made with higher torque and lower rpm. That would be foolish, 300hp is 300hp, all you have to do is gear the other motor deeper and you can get just as much torque out of it at the same truck speed. If that's why you bought your truck then I'd have to say yes, you did waste your money.
I bought a 300hp Duramax because it offers better fuel efficiency and more longevity than a 300hp gasoline truck. That's worth the premium I paid for the diesel motor, to me. I don't feel like it's wasted money at all.
hunter98
01-17-2002, 22:59
Arveetek, at least someone is finally getting it! 300 HP is 300 HP, for acceleration the Average HP across the RPM band that is used IE 2000-3300 RPM's is what provides the differences in acceleration, a low torque motor that must make very high RPM's to produce its peak HP, looses too much steam with every downshift, and spends many RPM's at lower power.
A 6.0L that is geared properly, to run at peak power at a given speed should be able to maintain the same as a duramax at peak power with the same load. But who wants to have to Run around towing at 5000 RPM's with the 6.0L, imagine the longevity, fuel milage, and noise of that motor. Also, if the Duramax produces 520 ft lbs at 1200 RPM's, and the 6.0L produces 300 ft lbs at 1200 RPM's, the Diesel has 73% more HP available at that RPM to get the load started.
Enough said
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
Hunter, you're right, but keep in mind that the gas motor is geared deeper, which mitigates the problem of getting the load moving and takes away much of our advantage there.
I think the difference here is where you want your rpm to be.
Sure the gasser will out-pull the diesel, but geared down to 6000 rpm isn't the most desirable place to be. I think that's the difference. Higher torque brings your rpms down to reasonable levels.
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter, Straight Piped PIC (http://uscom.com/~hoot/cars/duramax/gmc/exhaust/jvn03.jpg)
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Hoot: Exactly!
Mark: My posts weren't intentionally condescending, I genuinely thought you still weren't getting it because of some grossly inaccurate things you said. So I was trying to simplify as much as I could and present more ways of looking at it. I'm thrilled to see that you've got it and if your anger at me is the price, well, okay. But you've come a long way on this subject, from where you were to where you are. I think that's great.
I don't think you're a moron at all. Not even really sure what the word means. You strike me as someone who overcame his preconceived notion about a tricky subject. To me that means you're smart.
I think if you examine my posts a little more carefully you'll see that I wasn't trying to say all 300hp engines are the same, only that they're all capable of putting the same torque to the rear wheels for a given ground speed. Nothing else. There are probably a few places where I neglected to specifically qualify "horsepower is what matters" by saying "for performance", but it was within the context of the discussion.
Of course the motors aren't the same. If they were the same, who in the world would pay an extra $5000 for a diesel? Not me!
They run at different rpms, they use different fuels at different rates, they have different power curves, etc.
Anyhoo, it's been fun, and despite your anger, I'm gratified that you've got it.
I think this horse is dead. Hopefully bbugg has got it by now, too. If not, let's just agree to disagree, this is getting ridiculous.
[This message has been edited by ZFMax (edited 01-18-2002).]
arveetek
01-18-2002, 08:47
WAIT A MINUTE!!!
I hate to beat a dead horse, but, last night I thought I was beginning to understand all of this. But now I think I'm back to my original conclusion.
Okay, so let's say we have two different motors, both are 300HP, however, one makes 300HP at a low rpm, and the other makes 300HP at a high rpm. You could say the first engine is the Duramax, and the other is the 6.0L gasser.
Now, granted, we could gear the 6.0L truck to pull the same as the Duramax. However, we would have to be running high in the rpm band all the time where the HP is, correct?
The Duramax can pull the same load at a much lower rpm where the power is. Both trucks putting the same torque to the rear wheels.
Now, if the 6.0L was put in the Duramax truck, it wouldn't pull worth a darn, it would be geared wrong. So, using math, we could apply some sort of gear reduction to the 6.0L to make it pull like it had the Duramax.
But, who wants to drive a truck with low gears and a screaming engine? That's why the Duramax is a superior engine to the 6.0L, because it is more effecient, because it makes its power at a lower rpm. Unless I missed something, isn't this a direct result of the high torque of the Duramax? Isn't the high-torque, low rpm motor going to do a better job than the low-torque, high rmp 6.0L?
When this discussion started, it basically was "Torque is what is important" vs. "HP is what is important." Well, one without the other is meaningless.
Maybe to somebody who understands physics, they can deduce what they need from just the HP figure. But, what most of us want to know, is, at what rpm is that HP made?
If we're looking at several trucks to buy, and all of them are 300HP, we want to buy the truck that makes that 300HP at the lowest rpm, to make life easier. Wouldn't the easiest way to figure out which did so would be to look at the torque figures? Wouldn't the highest-torque 300HP be able to produce the power at a lower rpm, thus being able to give us the best effeciency and drive-ability?
The example of the V-8 gasser in the semi truck is a little unfair, I think. Sure, we could apply enough gear reduction to make it work, but it would do an awfully lousy job, the engine wouldn't last long, etc. etc., so the high-torque engine would be a better choice.
Basically, if I thought this thru right, both arguments are correct.
If one truck has a lower HP than another, it's not gonna make it to the top of the hill first.
If both trucks have the same HP and are geared properly, they'll both get to the top of the hill together. However, if one has more torque than the other, it can do a better job in the long run, and be much more pleasant to operate, though still not beating the other.
These are just the thoughts floating around in my head! http://www.62-65-dieselpage.com/ubb/biggrin.gif
arveetek
01-18-2002, 08:49
I posted my last remarks before ZF's last post, so now I see that I'm leaning towards being right!!
You're right, clearly you've got it!
There's only one little line I have a tiny bit of an issue with, but the rest of your text clearly shows you understand.
When this discussion started, it basically was "Torque is what is important" vs. "HP is what is important."
You gotta hang "for performance" onto that! I'm pretty sure I did that in every place I said HP is what's important.
Well, one without the other is meaningless.
For understanding how much torque can be put to the rear wheels for a given ground speed (i.e. performance), only the horsepower is meaningful. It can be made of ANY combination of torque and rpm at the engine, and we use gear reduction to convert it to the combination we want at the rear wheels.
It would be more accurate to say "torque without rpm is meaningless", at least with respect to performance. And the two of them together is called horsepower.
But of course, as you clearly point out, for considerations other than the performance, torque is VERY meaningful, because it tells us the engine makes it's power at low rpm. And that's a WONDERFUL thing!!! It makes the truck worth at least $5000 more in my opinion!
Posts like yours are very gratifying to me, thanks.
[This message has been edited by ZFMax (edited 01-18-2002).]
There is no right or wrong. What ZFMax has proven is that given one constant (5252) you can manipulate the other vaiables to get the desired ouput (Not trying to imply deception here).
He simply used the formula to say that given a constant HP rating (300) and the constant of 5252 you can prove that the same horsepower can get different amounts of torque to the ground through gear reduction. What I tried to prove (and didn't do a good job)was that "Horsepower is not what is important"
It is the combination of the two at a given RPM and how their curves relate to each other throughout the RPM range (they always cross @ 5252).
I feel that what is important is HP and torque (both) down low in the RPM curve. Diesel engines can due this. A gas engine can do it (through gear reduction), but at a higher RPM which normally comes at a cost(efficiency and longevity).
There is not right answer, because it isn't one over the other. There is a relationship between the two, and they can't be seperated and you can't take one over the other.
[This message has been edited by MABurns (edited 01-18-2002).]
"A steam engine turn fairly slowly. 600 rpm is not an unusual or "slow" turning speed. Don
Doggone it, Mark, you're saying inaccurate thigs again. I really thought you had it. I'm NOT trying to belittle you here, but the statements are wrong.
What ZFMax has proven is that given one constant (5252) you can manipulate the other vaiables to get the desired ouput (Not trying to imply deception here).
Keep in mind that I didn't just make up the 5252. It's the definition of a horsepower. 1 foot/lb of torque at 5252rpm is 1 horsepower. Always. For all motors.
He simply used the formula to say that given a constant HP rating (300) and the constant of 5252 you can prove that the
same horsepower can get different amounts of torque to the ground through gear reduction.
No, actually I've been pretty focused on showing that at a constant HP rating, you get the same torque to the ground for a given ground speed, regardless of the torque rating of the motor.
What I tried to prove (and didn't do a good job)was that "Horsepower is not what is important" It is the combination of the two at a given RPM and how their curves relate to each other throughout the RPM range (they
always cross @ 5252).
How the horsepower and torque curves relate to each other throughout the rpm range does not vary from one motor to the next. It's always exactly the same. There's a formula that describes the relationship. hp = (torque * rpm) / 5252. Always. For all motors.
I feel that what is important is HP and torque (both) down low in the RPM curve.
Saying both the torque and the horsepower matter at some certain rpm makes no sense. There's a fixed relationship between those two numbers at any given rpm. If two motors have the same torque at the same rpm, they have the same horsepower at that rpm. Always.
You've made a point of saying that torque and hp always cross at 5252rpm, which is correct. But what about 1500rpm? Did you know that at 1500rpm, torque is always 3.5 times the horsepower? And at 2000rpm, torque is always 2.6 times the horsepower? And at 10,000rpm, torque is always 52.5% of the horsepower?
There's a very fixed relationship between torque, rpm, and horsepower. This relationship does not vary with different kinds of motors.
[This message has been edited by ZFMax (edited 01-18-2002).]
Lone Eagle
01-18-2002, 22:04
ZFMAX, Your #48 post says it all as far as I am concerned. My DMAX will pull the wheels of my 5 th. wheel from 1500 to 3000 RPM. At 3000 no one but another DMAX is going to keep up on the hills. Later! Lone Eagle
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2002 2500 HD EC,SB,Back Country Bars, B&W Hitch, Pace-Edwards Roll Top Cover.
a64pilot
01-19-2002, 08:07
OK,
I have to enter into this in my uneducated redneck mechanic way.
My question is this, Back in the mid 70's I had a D***e W200, a 3/4 ton 4wd truck. It ran fine, accelerated well, but wouldn't pull the hat off of your head. I replaced the cam with an "RV" cam and took the 4bbl and manifold off and on with a 2 bbl. I lost horsepower, the truck wasn't nearly as quick in acceleration, but it would pull better. I had always assumed that I had decreased horsepower and increased torque. At least that is what I had been told by all the other rednecks.
What you are telling me I believe is that I lost peak power period, just simply moved the peak power point down to a lower RPM. and the fact that the truck would pull better was actually an illusion?
Lastly if TQ. is irrelevant, why do all of the manufactures quote it?
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2001 C3500 Charcoal Grey
Putco Boss Boards
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Catch All Mats
Q: What would've happened if you had geared it down instead of moving the engine's powerband down?
A: For a given ground speed, you would've had MORE torque to the rear wheels.
FACT 1: for understanding how much torque you can put to the rear wheels at any given speed, how much you can multiply the engine's torque by (with gearing) is just as important as how much torque it produces.
FACT 2: For any given target vehicle speed, the more rpm the engine has, the more you can gear it down and the more you'll multiply it's torque.
FACT 3: For evaluating performance, engine torque alone only tells half the story. What good is it to know how much torque you have if you don't know how much you can multiply it by, for a given target speed?
FACT 4: For evaluating performance, engine rpm alone only tells half the story. For a given target speed, what good is it to know how much you can multiply the torque by if you don't know the torque?
FACT 5: Because it's the product of BOTH the torque produced AND the amount we can multiply it by for a given target speed (aka rpm), horsepower alone fully describes the performance capability of a motor. Torque and rpm are both built into the number.
FACT 6: For any given ground speed, a truck will always pull hardest if it's geared to put it's motor at it's horsepower peak, because that's the point where the combination of torque and rpm are the highest.
Anyone disagree with any of those? Well, they're all easily provable facts.
If someone's genuinely interested in understanding these facts, I'll continue trying to help. But I have to ask you to let go of preconceived notions, and approach it logically, not emotionally. Otherwise we'll just be wasting our time.
[This message has been edited by ZFMax (edited 01-19-2002).]
Lastly if TQ. is irrelevant, why do all of the manufactures quote it?
Torque is most certainly relevant. Anyone who tells you otherwise is blowing smoke. It's a major part of the horsepower equation.
The other part is rpm.
Torque by itself, without rpm, is pretty irrelevant, though, at least for evaluating performance. As is rpm without torque. Each one only tells half the story. So either one is meaningless without the other.
Don't believe me?
Do you want 2,626 ft/lbs of torque in your truck? In my very first example, I show you how to do it with a handheld electric drill motor. If torque by itself is meaningful, yank that Duramax and stick a drill motor in there.
Just be prepared to go reeeeeaaaal slow.
To have a meaningful number, you have to consider both the torque and the rpm it's made at.
The parameter that describes the combination of both torque, and the rpm it's made at, is called horsepower.
Within the context of the manufacturer's claims, a high torque rating means it's power is made with a combination of higher torque and lower rpm than other motors.
But, the fact that it's power is made with higher torque and lower rpm does not mean it can pull a trailer up a hill or accelerate faster than another truck with lower torque at higher rpm and the same horsepower.
Ultimately, the motor with the highest COMBINATION of torque and rpm (aka "horsepower") will put maximum torque to the rear wheels for any given speed. This is because more gear reduction can be applied to the lower torque/higher rpm motor and still get to the same ground speed. That extra gear reduction multiplies the lower torque and makes up for the deficit. Refer to the 6 facts above.
What's so cool about a high torque/low rpm motor is that it lasts a long time and it's fuel efficient. Not that at out-tows a properly geared low torque/high rpm motor of the same horsepower. It doesn't.
There, I did a whole post without any math.
Man, if someone doesn't get this by now, they probably never will.
[This message has been edited by ZFMax (edited 01-19-2002).]
I will probably get death threats for revisiting this topic, but I think this is a great post and it taught me a bunch!
There are just a couple of things I'm unclear on.
1. Does the manufacturer state the torque levels in a motor specifically to illustrate where in the RPM range (how low) the engine is making it's torque? This would support the low RPM / engine longevity argument well. Aside from that, I see no real benefit in publishing those numbers if gearing can mitigate nearly any engine's torque shortcomings. This question was addressed well by Hoot, I just want to see if I understand correctly.
2. What design characteristics does a diesel engine possess that enable it to produce gobs of torque at such low RPMs. (Rookie question)
3. If the max torque could be slid to the right along the RPM band, wouldn't you realize an exponential increase in HP? I realize this would lead to higher RPMs while towing, but moving the max torque up 1000 RPMs doesn't seem too excessive and would give you a substantial HP increase. What factors limit a diesel's ability to produce more torque 'up high'?
Thanks to ZFMax for the physics lesson! I guess I never really understood the proper relationship between HP & TQ (probably still don't!)
Kevin
[ 06-01-2002: Message edited by: 2K2AD ]</p>
Aaaaaaaaarrrrrrgggggghhhhh! I can't believe this topic has come back!
Oh well ...
1) I'm not certain about their motivations, although I wouldn't be surprised if they're not just a little bit taking advantage of people's misconceptions (which as we can see run rampant). What I know for sure is how to interpret the number ... when they advertise a high torque figure with a more modest power figure (i.e. our Duramaxes), they're saying it makes it's power with a combination of relatively high torque and low rpm. They may well be hoping people interpret a high torque figure as somehow meaning higher performance, which of course, it doesn't.
2) Now THAT'S a great question! I'm not a motor designer, but as I understand it, two things create torque in an engine: the combustion pressure and the mechanical advantage it has on the crank, aka stroke.
Diesels basically run on ping, which as I understand it, means the fuel doesn't so much burn as explode. And this explosion causes a lot of pressure, hence creating more torque. But, for reasons I don't fully understand, there are limits to how fast you can repeat this process (rpm), possibly related to heat? I'm not sure, someone on here probably knows.
3) Ah-ha, finally a question I can answer. You got it, Toyota. A good motor tuner looks at his torque curve, because he knows it's showing the cylinder fill. Various parameters of the motor are optimized for maximum cylinder fill at a certain rpm, for example, the intake tract length, the valve timing (in particular the intake valve close event), and the exhaust design. Changing these parameters such that the torque peak moves to the right is the whole idea when you're going for max power. Move the torque peak to the right and the horsepower comes up!
I think you understand this stuff good.
Oh hey, I heard a GREAT analogy awhile back about torque, rpm, and hp ...
horsepower is like your paycheck. Torque is your pay rate and rpm is the number of hours you work.
Just like it does you no good to have rpm without torque, it does no good to work 100 hours a week if you're only getting paid $1 an hour, right? Your paycheck (horsepower) is small.
Likewise, torque without rpm isn't useful. It does no good to make $100 per hour if you only work 1 hour a week, right? Your pay (horsepower) is small.
What matters is the COMBINATION of pay rate (torque) and hours worked (rpm). That's what gives you a fat paycheck (horsepower).
With a diesel, we get a good paycheck (300hp), and we manage to get it without putting in a lot of hours (rpm) because we make a good rate of pay (torque). Thus, we don't work ourselves to death. Gassers make good money too but they have to put in a bunch more hours than us to do it, hence they don't last as long.
Another good analogy is the hammer and nail. Say you've got 10 seconds to drive in a nail. You can do it with 10 whacks of a 1lb. hammer, at 1 second per whack. That's high rpm and low torque. Or you can do it with two whacks of a 5lb hammer at 5 seconds per whack. That's high torque and low rpm. Both are the same horsepower, they got the same amount of work done in the same amount of time.
[ 06-01-2002: Message edited by: ZFMax ]</p>
Chevy2DMAX
06-02-2002, 16:31
Now, how about a lesson on air density, power loss and turbos?
What great answers! I must have read parts of this post 50 times. Just when I thought I had a handle on it, someone would retort with what seemed like a valid contradiction.
I think I've got a good handle on it now. I'll second the misconception of the public part, before this post that is what I believed as well.
Thanks again!
Kevin
hdmax(mike)
06-02-2002, 17:29
After reading about 12-15 post, I decided that if I were to learn something here I would have to read ZFMax post only. I think I learned a little.
I think my head hurts from reading all of the above ... but right now,I'm not even sure of that... called my wife to read these post (she's only taught high school physics for over 37 years (yes 37) and she says ZF seems to have a pretty good handle on things :confused:
Keep the posts coming!!!
This is my attempt at a record setting topic, almost 4 pages now.
What a Monday morning!!! I normally start out my work day reviewing the forums I frequent. Little did I know I'd stumble on this jewel and spend 4 count'em 4 hours going over it. Digging out the Machinery's Handbook and other sources, and pouring over notes I made to decipher the thread. So like it or not after that much time I'm gonna post!!!!!
ZFMAX, you did a good job with the torque vs horsepower comparision. I spent 7 years in the industrial clutch and brake field and this made me dust off stuff I haven't used for a couple years.
Thanks for the positive comments, guys, I appreciate it.
Sorry, I don't really know the answer to the question on turbo's and altitude. I would *guess* that it depends on whether the wastegate operates on relative or absolute pressure, but that's just a guess. There's probably more to the story.
I must be living right, I filled my truck at lunchtime today and got a new high, 19.9mpg, and yes, I topped it off good. I haven't seen 19's since I first got the truck last fall, all winter long it was 17's with a few 18's popping up this spring. Not sure if I just got a great tank of fuel or if the motor just likes hot weather, this last tank was run through with temps in the 90's.
My squeaky clutch pedal is fixed, the 900rpm vibration noise is fixed, and the SES light from using the block heater is fixed (not that I use the block heater this time of the year). If I can just get that !@#$% steering rattle fixed, I'll be in truck heaven.
Speaking of which, stopped by the Ford dealer today to pick up some parts for the wife's Expedition. Looking at a new F350 on my way out, a salesman approached. Did you know they have an 18% failure rate on Duramax engines? Yepsiree, they break left and right. At least a couple hundred folks have brought their Duramaxes in, BEGGING the Ford dealer to take'em in trade, they're so bad! Unbelievable. This sales guy claimed 34 years in the business, he's "in-the-know"! 'Course, when I asked him the GCWR on the F350 I was looking at, he proceeded to describe GVWR. "No, GCWR", says I. "Never heard of it, I don't think Ford rates that." Uh-huh. I found it in his book and showed it to him. 34 years in the business, what an expert. 20K in case anyone cares.
[ 06-03-2002: Message edited by: ZFMax ]</p>
Chevy2DMAX
06-03-2002, 18:26
My air density/turbo comment was kinda leaning towards comparing gas engines to diesels. I agree that horsepower is horsepower, but in a gasser horsepower can drop significantly with altitude AND temperature. So, before anyone thinks a 6.0 (or even 8.1) might whip a Duramax--that would be at sea level on a cool day.
So you're saying the wastegate works on absolute pressure? Instead of pressure relative to the current atmospheric pressure?
If it works relative to the current atmospheric pressure, the real boost pressure will drop with altitude, and therefore, uncorrected horsepower will drop as well. But, it may well work on absolute pressure as you say, I'm not denying that, I honestly don't know.
It'd be interesting to dyno one of these trucks at sea level and then at altitude and see the difference.
Amianthus
06-05-2002, 12:23
Okay, here's my hat. (don't make me eat it)
I just spent a ton of time figuring out dyno's, HP, torque, RPM, gearing and on and on. Here's what I can tell you about what I've learned.
There are basicly two types of dynos. Inertial and retarder (brake type).
When you use an inertial dyno to measure power, you are using a given rotational mass and accellerating it (Dynojet). Based on the accelleration curve, speed of the drum, time, and mass of the drum you can calculate HP. It takes a certain amount of work (HP) to move that mass. This type of test measures HP only and torque is calculated based on the above formula (HP=T*S/5252).
Then there is a brake (retarder) dyno. There are several types of brakes and it really doesn't matter what type of brake it is (unless you really want to split hairs). These dynos are used by labs, engine builders, manufacturers, etc. The reason being that the control conditions can be duplicated quite accurately. Not to mention, it gives a more ture reading of an engine's performance.
The way they work is that an engine is brought to a given speed and held there. Then the brake is used to put load on the engine until the engine starts to lose against the brake (full throttle on the engine at that speed). The brake requires a certain amount of force to resist the engine. That force causes the brake to deflect (Torque). There is a strain gauge that measures the amount of deflection of the brake. This deflection is converted to ft-lbs. You take these data points and plot them and voila, you have your graph.
Now in this dyno, torque is measured. But you have RPM so you can calculate HP. Typically, the dyno run consists of running the engine up to the governor and bringing the engine down with the brake and then allowing it to come back up to the governor taking data readings on the way back up.
Now advertised readings for an engine are usually taken at the flywheel (as measured by the latter dyno). The Dmax gives 300 HP and 520 ft-lbs as peaks. Being that torque is a measure of force, torque is usually stable through the drive train (give or take). You can multiply this force with gearing as was stated above. The drivetrain takes a certain amount of work to function (approximately 20% but that varies widely). I heard around 60 HP for the Dmax. So a HP reading at the rear wheels for a stock D/A should be around 240 HP. I think this is reasonable.
As for the gearing to match performance between gassers and diesels. It's not really gonna happen. The reason being that, you can only modify torque through gearing. HP won't change. If you raise the torque by gearing, you will lower speed (RPM) proportionately. That means that HP will be constant. The benefit of a diesel over a gasser is that it takes less RPM to make the same amount of HP that a gasser can. That means that torque (force the engine can make) is higher.
Torque is what makes the truck move. HP is how fast it can move it. For example, a gasser and a diesel with the same HP ratings (gearing, tranny, everything being the same) will take the same amount of weight and move it the same distane (or to the same ultimate speed). A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).
I surely hope that I didn't muddy the waters any. If I did, sorry. If you have more questions, or if I wasn't really clear about something (it happens), post it and lemme know. I'll try to explain it better.
Amianthus
06-05-2002, 12:26
Okay, here's my hat. (don't make me eat it)
I just spent a ton of time figuring out dyno's, HP, torque, RPM, gearing and on and on. Here's what I can tell you about what I've learned.
There are basicly two types of dynos. Inertial and retarder (brake type).
When you use an inertial dyno to measure power, you are using a given rotational mass and accellerating it (Dynojet). Based on the accelleration curve, speed of the drum, time, and mass of the drum you can calculate HP. It takes a certain amount of work (HP) to move that mass. This type of test measures HP only and torque is calculated based on the above formula (HP=T*S/5252).
Then there is a brake (retarder) dyno. There are several types of brakes and it really doesn't matter what type of brake it is (unless you really want to split hairs). These dynos are used by labs, engine builders, manufacturers, etc. The reason being that the control conditions can be duplicated quite accurately. Not to mention, it gives a more ture reading of an engine's performance.
The way they work is that an engine is brought to a given speed and held there. Then the brake is used to put load on the engine until the engine starts to lose against the brake (full throttle on the engine at that speed). The brake requires a certain amount of force to resist the engine. That force causes the brake to deflect (Torque). There is a strain gauge that measures the amount of deflection of the brake. This deflection is converted to ft-lbs. You take these data points and plot them and voila, you have your graph.
Now in this dyno, torque is measured. But you have RPM so you can calculate HP. Typically, the dyno run consists of running the engine up to the governor and bringing the engine down with the brake and then allowing it to come back up to the governor taking data readings on the way back up.
Now advertised readings for an engine are usually taken at the flywheel (as measured by the latter dyno). The Dmax gives 300 HP and 520 ft-lbs as peaks. Being that torque is a measure of force, torque is usually stable through the drive train (give or take). You can multiply this force with gearing as was stated above. The drivetrain takes a certain amount of work to function (approximately 20% but that varies widely). I heard around 60 HP for the Dmax. So a HP reading at the rear wheels for a stock D/A should be around 240 HP. I think this is reasonable.
As for the gearing to match performance between gassers and diesels. It's not really gonna happen. The reason being that, you can only modify torque through gearing. HP won't change. If you raise the torque by gearing, you will lower speed (RPM) proportionately. That means that HP will be constant. The benefit of a diesel over a gasser is that it takes less RPM to make the same amount of HP that a gasser can. That means that torque (force the engine can make) is higher.
Torque is what makes the truck move. HP is how fast it can move it. For example, a gasser and a diesel with the same HP ratings (gearing, tranny, everything being the same) will take the same amount of weight and move it the same distane (or to the same ultimate speed). A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).
I surely hope that I didn't muddy the waters any. If I did, sorry. If you have more questions, or if I wasn't really clear about something (it happens), post it and lemme know. I'll try to explain it better.
I would like to thank everyone who has posted under this thread. The effort to provide extended technical information in a manner that can be understood by all commendable. A greater understanding of torque vs. horsepower and how the figures are developed has been rewarding to all. Unfortunately, I am just not that mechanically inclined. I will remember the basics though:
1. Press with right foot and go.
2. With diesel press right foot and tow.
Thanks for all the hard work. smile.gif
Philip
Amianthus: OK, you invited questions, I'm gonna lay'em on ya ...
>>>>Being that torque is a measure of force, torque is usually stable through the drive train (give or
take).<<<<
At ANY point in the powertrain, anywhere you select, the formula hp = (torque x rpm) / 5252 has to apply, right? Crank, inside the tranny, driveline, rear wheels, whatever, that relationship between horsepower, torque, and rpm is always true, for any rotating shaft. The formula defines it that way.
So if drivetrain losses are eating horsepower, don't they also have to eat torque and/or rpm? How can I keep torque and rpm the same and have less horsepower?
>>>>Torque is what makes the truck move.<<<<
Is it torque at the engine that makes the truck move? Or torque at the rear wheels?
If it's torque at the rear wheels, doesn't gear reduction between the engine and the rear wheels affect that number?
If the engine's rpm is higher, can't more gear reduction be applied for a given rear wheel speed?
If more gear reduction is applied, doesn't that increase the torque at the rear wheels?
Ultimately, doesn't the highest *combination* of torque and rpm at the engine determine the torque at the rear wheels for any given speed?
Isn't the *combination* of torque and rpm called "horsepower"?
>>>>A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).<<<<
Wait, doesn't the highest rear wheel torque accelerate the fastest?
And didn't we just show that highest rear wheel torque at any speed come from the highest combination of torque and rpm (horsepower) at the engine?
So let's say I've got two trucks side by side, one a torquey diesel, the other a peaky gasser. Both are the same weight and have the same size tires Both are at full throttle and making 300hp and going the same speed. The diesel has a whole bunch more torque than the gasser.
Which will accelerate faster?
Both have 300hp at the rear axle, right? And they're going the same speed, right? So the rear wheel rpm is the same, right?
Well, if the hp at the rear wheels is the same, and the rpm at the rear wheels is the same, doesn't the torque at the rear wheels have to be the same, too? Doesn't the formula say so?
So why would the diesel accelerate faster?
[ 06-05-2002: Message edited by: ZFMax ]</p>
Amianthus
06-06-2002, 09:46
>>>>Being that torque is a measure of force, torque is usually stable through the drive train (give or
take).<<<<
At ANY point in the powertrain, anywhere you select, the formula hp = (torque x rpm) / 5252 has to apply, right? Crank, inside the tranny, driveline, rear wheels, whatever, that relationship between horsepower, torque, and rpm is always true, for any rotating shaft. The formula defines it that way.
So if drivetrain losses are eating horsepower, don't they also have to eat torque and/or rpm? How can I keep torque and rpm the same and have less horsepower?
That's a very good question. Yes, you will lose torque as based on that equation which applies throughout the driveline. I should've chosen my wording a little better. Actually, I don't know what I was thinking. You are right on this point. Drivetrain losses amount to around 20%. Now this varies from vehicle to vehicle, and there is a super complicated formula that will allow you to accurately determine driveline losses. But I just stick with 20%.
>>>>Torque is what makes the truck move.<<<<
Is it torque at the engine that makes the truck move? Or torque at the rear wheels?
If it's torque at the rear wheels, doesn't gear reduction between the engine and the rear wheels affect that number?
Torque at the engine is what makes the truck move. Yes, gear reduction does affect torque at the rear wheels. So does OD in your transmission. What also comes into play is wheel speed (RPM). If you take the torque at the rear wheels and the rpm of the rear wheels, you can calculate HP. You will see that a 3.0 rear will have the same HP as a 6.0 rear end ratio. The 3.0 will spin faster and thus have less torque to the ground. The 6.0 will have greater torque but spin slower. They will both have the same HP (all other things being equal).
If the engine's rpm is higher, can't more gear reduction be applied for a given rear wheel speed?
If more gear reduction is applied, doesn't that increase the torque at the rear wheels?
Ultimately, doesn't the highest *combination* of torque and rpm at the engine determine the torque at the rear wheels for any given speed?
Isn't the *combination* of torque and rpm called "horsepower"?
Yes. More torque would be made, but at the sacrifice of wheel speed (RPM). RPM is independent of torque.
So no. Combinations only apply when HP is being calculated. We are assuming that HP is a constant in this discussion (aren't we?).
Yes, the combination is used to determine HP.
>>>>A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).<<<<
Wait, doesn't the highest rear wheel torque accelerate the fastest?
And didn't we just show that highest rear wheel torque at any speed come from the highest combination of torque and rpm (horsepower) at the engine?
So let's say I've got two trucks side by side, one a torquey diesel, the other a peaky gasser. Both are the same weight and have the same size tires Both are at full throttle and making 300hp and going the same speed. The diesel has a whole bunch more torque than the gasser.
Which will accelerate faster?
Both have 300hp at the rear axle, right? And they're going the same speed, right? So the rear wheel rpm is the same, right?
Well, if the hp at the rear wheels is the same, and the rpm at the rear wheels is the same, doesn't the torque at the rear wheels have to be the same, too? Doesn't the formula say so?
So why would the diesel accelerate faster?
That's a very good question. After looking at my post, I realized that I should've chosen my wording much better (again, don't know what I was thinking). I should've stated that a diesel will get to it's peak HP faster than a gasser. That would've been more accurate.
It goes like this. The diesel makes it's peak HP at about 2700 RPM (mine, not yours). So I hit peak HP pretty fast. Where a gasser hit's it's peak HP at around 4500 RPM. It would take the gasser longer to hit peak HP because it has less torque. In this example, my diesel would be making 584 ft-lbs torque at peak HP. The gasser would be making 350 ft-lbs at it's peak HP. So for the same amount of HP, the diesel makes more force to move it's load.
Now assuming a 1:1 transmission in both and a 1:1 rear end in both, the diesel would be only turning the wheels at 2700 RPM at peak HP. That's not nearly as fast as the gasser that will turn it's wheels at 4500 RPM. The diesel just gets there faster. If you were to leave the diesel alone and give the gasser a 1:1.66 ratio, the gasser and the diesel would have the same wheel speed and torque. The engines would be the same, but the gear reduction would equalize the performance between the two.
The statement you made about the HP, and wheel speed being the same therefore torque would be the same is not quite right. RPM wouldn't be the same. It couldn't because the RPM at which both engines make peak HP are different.
The diesel accelrates faster because it hit's it's peak HP faster. Because of more torque for a given RPM. Yes, gear reduction will help the gasser with torque at the sacrifice of wheel speed (RPM).
The biggest benefit to the diesel is it's torque. We know this. This is the force that is generated by the engine (not the work). If it takes 250 ft-lbs to move the load, then both would be able to handle the work (although the gasser would be working harder to maintain it). Then you encounter a hill and it now takes 400 ft-lbs to keep the load moving. The diesel will be able to resist slowing down more efficiently than the gasser, because now the gasser engine has to slow down until it hits an equilibrium RPM when torque matches 400. Downshifting will help accomplish this, but you sacrifice speed. But the diesel can still move the load as it does not have to downshift because the available torque to move the load is higher than is required at 300 HP.
I hope this cleaned things up a little. If you have more questions (or catch another bad choice of wording), post it.
Sigh. Okay, Let's try again.
>>>>Torque at the engine is what makes the truck move<<<<
'Scuse me? You're saying the torque at the engine is more significant for making the truck move than the torque at the rear wheels? Seriously?
So why do we need all these gears in our tranny and rear axle? I mean, if that engine number is all that matters, why do we try so hard to change it before it gets to the rear wheels?
>>>> Yes. More torque would be made, but at the sacrifice of wheel speed (RPM). RPM is independent of torque. So no. Combinations only apply when HP is being calculated. We are assuming that HP is a constant in this discussion (aren't we?).<<<<
You missed where I said "at any given speed".
Look, this is really a very simple concept. Let's take an example.
We have a diesel that's turning 2000rpm and making 400ft/lbs of torque. That's 152hp, right?
We have a gasser that's turning 4000rpm and making 200ft/lbs of torque. Again, that's 152hp, right?
Let's say we gear the diesel 5:1 overall (trans x rear end). Therefore, the rear wheels are turning 400 rpm, right? 2000rpm divided by 5 = 400rpm. What's more, the rear wheels have got 2000ft/lbs of torque, right? 400ft/lbs times 5 = 2000ft/lbs, right?
Let's say we gear the gasser 10:1 overall (trans x rear end). Therefore, the rear wheels are turning 400 rpm, right? 4000rpm divided by 10 = 400rpm. What's more, the rear wheels have got 2000ft/lbs of torque, right? 200ft/lbs times 10 = 2000ft/lbs, right?
So both of these trucks are going the exact same speed (400 rear wheel rpm) and have the exact same torque at the rear wheels (2000 ft/lbs) right? Assuming they're the same weight, and have the same size tires, the acceleration has to be identical, right? I mean, f=ma, that's the first thing they teach you in physics.
So if performance is identical, what in the world does it matter, performance-wise, whether the motor is making 400ft/lbs or 200ft/lbs?
Answer: it doesn't. What the gasser lacks in engine torque, it makes up for in engine rpm. Because it has more rpm, it can be geared deeper and still be going the SAME GROUND SPEED. The driver can be running a gear or two lower, or the rear end may have a shorter ratio, or some combination thereof, but the fact is, at any given ground speed, if it's making the same horsepower, it'll have the same torque at the rear wheels, regardless of the fact that it's only got half the torque at the engine.
>>>>I should've stated that a diesel will get to it's peak HP faster than a gasser. That would've been more accurate.<<<<
>>>>It goes like this. The diesel makes it's peak HP at about 2700 RPM (mine, not yours). So I hit peak HP pretty fast. Where a gasser hit's it's peak HP at around 4500 RPM. It would take the gasser longer to hit peak HP because it has less torque. In this example, my diesel would be making 584 ft-lbs torque at peak HP. The gasser would be making 350 ft-lbs at it's peak HP. So for the same amount of HP, the diesel makes more force to move it's load.Now assuming a 1:1 transmission in both and a 1:1 rear end in both, the diesel would be only turning the wheels at 2700 RPM at peak HP.<<<<
The problem with that example is you're talking about the same gearing for two motors that are running at radically different rpms, and therefore the trucks are running at radically different speeds. You're not looking at gearing as something that can (and should) be different between a gasser and a diesel. Basically what you're saying is "hey, if I gear them the same, the diesel accelerates more quickly to a lower speed!" Yeah, so?
That's totally meaningless. My truck accelerates a whole bunch quicker in first to a lower speed than it does in 6th to a higher speed, too. So what? If anything, that makes my point. It's EASY to get rear wheel torque and accelerate quickly. Just put it in first. It's EASY to get rear wheel rpm and go real fast. Just put it in 6th. What's tough is to get both at the same time. As you gear for more rear wheel speed, the rear wheel torque drops. As you gear for more rear wheel torque, the rear wheel speed drops. Ultimately, what matters is how much of BOTH rpm and torque you can get at the same time. The combination. That's called horsepower.
This is EXACTLY why I've done all of my examples "at any given speed", something you seem to have overlooked. Unless you equalize the speeds through gearing, comparisons of torque to the rear wheels are meaningless. Yeah, sure, geared the same, the diesel delivers more torque to the rear wheels at a slower speed. So what? Take a gasser of the same horsepower, gear it to go that SAME SPEED, and it's gonna put just as much torque to the rear wheels! That's a fact, not an opinion.
>>>>The statement you made about the HP, and wheel speed being the same therefore torque would be the same is not quite right. RPM wouldn't be the same. It couldn't because the RPM at which both engines make peak HP are different.<<<<
See, you missed where I said "and going the same speed". With two different engine rpms, that implies they're geared differently. You've got to start looking at gearing as a variable, not a constant. It's very simple to change your gearing by just moving the shift lever. And of course, you can get a gasser with a shorter rear end.
>>>>The biggest benefit to the diesel is it's torque. We know this.<<<<
I know it, too. But I also know it's not a performance metric. It's an adjective that describes how the performance metric (horsepower) is provided. A high torque figure means the engine's horsepower is made with relatively low rpm. It doesn't somehow make my 300hp stronger than someone else's 300hp that's made with low torque and high rpm. Both will put the same torque to the rear wheels when geared for any given speed. The formula says so. If the rear wheels in both trucks have the same horsepower, and they've been geared to go the same speed, they MUST have the same torque. That was the point of the example in my previous post. There's no way around it, if you're going to follow the formula.
>>>>This is the force that is generated by the engine (not the work). If it takes 250 ft-lbs to move the load, then both would be able to handle the work (although the gasser would be working harder to maintain it). Then you encounter a hill and it now takes 400 ft-lbs to keep the load moving. The diesel will be able to resist slowing down more efficiently than the gasser, because now the gasser engine has to slow down until it hits an equilibrium RPM when torque matches 400. Downshifting will help accomplish this, but you sacrifice speed. But the diesel can still move the load as it does not have to downshift because the available torque to move the load is higher than is required at 300 HP.<<<<
You absolutely, completely, totally ignored the difference in engine rpm and gear reduction between the two trucks in that example.
The engine torque is totally irrelevant for determining whether the truck slowed down for that hill or not. All that matters is whether or not enough torque was reaching the rear wheels.
If those two trucks are making the same horsepower, and both are running the same speed (a difference in gearing is implied there), then they've got the same torque at the rear wheels. And therefore they will react to the hill in exactly the same way. The difference in torque at the engine has absolutely zero to do with anything.
In summary, you (and others who are confused about this) are trying to add way too much significance to the engine's torque figure with respect to performance. You understand that torque moves the truck, so you're immediately trying to draw a direct connection between engine torque by itself and performance. But there isn't any. Zero. Zilch. Nada. Why? Because it's rear wheel torque that moves the truck, not engine torque. And that's a hugely important distinction. You can't just gloss over it, you have to understand it. You can't go making up examples that ignore it, they're meaningless.
The engine's torque figure is nothing more than an adjective for it's horsepower. It's a number that's telling you that the engine's horsepower is made of high torque and low rpm, that's all. But gearing (trans and rear end) is all about taking whatever torque and rpm combination the engine provides and converting it into the torque and rpm makeup we need at the rear wheels. So the makeup at the motor is not significant for performance, we can easily convert it to whatever makeup we need. Only the total combination of torque and rpm really matters for performance. That's why we talk in horsepower when we're talking about performance.
If we had no gearing in between the engine and rear wheels, I would agree completely, the torque & rpm makeup of the engine's horsepower would be hugely significant for performance.
[ 06-06-2002: Message edited by: ZFMax ]</p>
Jumbo Jet
06-06-2002, 13:37
With all the laws of physics flying around here about horsepower, gearing, RPM, torque, etc., where does rotational mass come in to play???
You could take a 300 Horsepower V-8 Lexus engine and stick it in the Kenworth, compute all the rpm's, gear ratios, etc. and still not pull a sick wh-re off a p!ss pot!
Your numbers might all add up (fuzzy math), but you are still leaving some things out of the equation.
Any of you old enough to remember the 'poppin John' John Deeres. Wasn't a whole lot of HP, RPM, etc., but sure was a whole lot of rotational mass.
[ 06-06-2002: Message edited by: Jumbo Jet ]</p>
Amianthus
06-06-2002, 14:02
ZFMax, you keep throwing gear reduction into this and I was trying to keep gear reduction out of it.
To give a short reply to your above post, Yes. Gearing is the great equalizer between gassers and diesels. That's why one of our firetrucks a gasser engine needs 20 speeds to make it move, when a 6 speed diesel can do the same job. But the higher torque of the diesel allows us to not have to gear as much to what is most efficient. You have to gear down considerably to get a gasser to match the torque of a diesel. When you gear down you lose RPM. Agree?
Yes, you can convert the engine's output to what you desire, but at what cost. If you gear down for torque, you lose speed. If you gear up for speed, you lose torque. This is obvious.
Leave gear reduction out of this as it has nothing to do with the advertised numbers a manufacturer publishes. Gear reduction has absolutely no effect on HP. NONE!!! I know you must know this. You can't make the arguments you are and not know this. Gear reduction changes torque and RPM. So to use your argument, if you want a gasser to produce torque like a diesel, throw more gears at it. But the HP will be the same. Always. I don't see how this is any different than what I have said pertaining to flywheel measured torque and rpm. Outside of a bad choice of some wording.
It seems that you believe that HP is the be-all end-all of performance. Where I believe that torque is the root. Horsepower is a calculated term of torque and RPM. Horsepower is calculated as force over time. Well, time is a base measurement. Force is a base measurement. Horsepower is a derived measurement. You don't measure horsepower, you calculate it. So when you say that torque is just an adjective of an engine's horsepower, I can say that the opposite is true. Horsepower is an adjective of an engine's torque, since horsepower is not measured but calculated.
BTW-This isn't personal, so don't take it that way.
Rotational mass doesn't create power. It merely stores it. It slows down acceleration because part of the energy being produced is put into storage, instead of converted to power at the rear wheels. It gets used later when a load is applied that exceeds the ability of the engine to meet it.
More rotational mass can be applied to a gasser or a diesel. So introducing it into this discussion does nothing to dispel the misconception that diesel horsepower is somehow stronger than gasser horsepower because it's made of higher torque and lower rpm, which is really what this discussion is all about. It would only add more complication and confuse people and it has nothing to do with the core issue.
You want to know the next one I'd add if we were really going start analyzing performance at the next level? Area under the curve. Basically, figure out the operating RANGE of each motor and integrate the horsepower produced over that range.
But it's not necessary to prove my point, and besides, you gotta walk before you run. Until people understand the basic relationship between horsepower, torque, rpm, and gearing, trust me, you don't want to get into area under the curve.
The math behind this is pretty basic, if you know how to multiply and divide it shouldn't be the least little bit fuzzy to you.
Properly geared, the 300hp Lexus motor would pull the Kenworth just as hard as *any* other 300hp motor. Even one with 1000 ft/lbs of torque. If you understand the relationship between hp, torque, and rpm, and you understand the effect of gearing, this is obvious.
>>>>ZFMax, you keep throwing gear reduction into this and I was trying to keep gear reduction out of it.<<<<
Finally something we agree on!!!
>>>>That's why one of our firetrucks a gasser engine needs 20 speeds to make it move, when a 6 speed diesel can do the same job. But the higher torque of the diesel allows us to not have to gear as much to what is most efficient.<<<<
Aw, now the discussion is changing. You're saying the diesel has a wider powerband than the gasser, and therefore can have wider spacing between it's gears and get away with less gears!
Well, I'm pleased to see you clarifying your position, but the truth is diesels generally have a narrower powerband than gassers. I can prove that. But not now, you've left me too many other things to refute.
>>>>Yes, you can convert the engine's output to what you desire, but at what cost. If you gear down for torque, you lose speed<<<<
What you're missing in that statement is that you're starting from a higher speed with the gasser, and therefore when you gear down and lose speed you come down to the same speed as the diesel. And that makes it a fair comparison.
Take my 2000rpm diesel & 4000rpm gasser example. Yes, we have to gear down the gasser twice as much as the diesel, of course. But that puts it at the exact same speed as the diesel! And that's the only fair way to compare the rear wheel torque of the two, at the same speed.
Therein lies the value of turning more rpm. You can apply more gear reduction than the lower rpm motor, and yet end up at the same speed! And since you applied more gear reduction, you make your lesser engine torque into just as much rear wheel torque. As it turns out, the rpm at which the engine makes it's torque is JUST as important, for performance, as the amount of torque it makes! Which is why horsepower is the meaningful number, it has BOTH torque and rpm built into it!
>>>>Leave gear reduction out of this as it has nothing to do with the advertised numbers a manufacturer publishes. Gear reduction has absolutely no effect on HP. NONE!!!<<<<
Of course not. But it has a HUGE effect on how that horsepower is made up, i.e. it's mix of torque and rpm. And the mix of torque and rpm at the rear wheels is the name of the game. The rear wheel rpm is your speed, the rear wheel torque is your ability to accelerate or pull a load up a hill. If you want to ACCURATELY compare a diesel to a gasser, you have to consider that each NEEDS to be geared differently. Comparing them at the same gearing tells you nothing. The gasser would be going a whole lot faster with a whole lot less rear wheel torque available.
>>>>It seems that you believe that HP is the be-all end-all of performance.<<<<
I sure do! But it's not so much a case of believing. These aren't things we can have opinions on, these are physical laws. It's more a matter of understanding than believing.
>>>>Where I believe that torque is the root.<<<<
Okay, yank your Duramax and replace it with a 1/2 hp, 1000rpm hand held drill motor geared 1000 to 1. Instead of that wimpy 520ft/lbs of torque, you'll have a whopping 2,626 ft/lbs of torque!
Problem is, it'll only turn 1 rpm. Yeah, you can pull a trailer, you'll just be pulling it *real* slow!
You see, when you're talking about performance, the rpm is every bit as important as the torque. That's why we talk horsepower. Horsepower is torque x rpm, it has BOTH of the important figures rolled into one.
>>>>Horsepower is a calculated term of torque and RPM<<<<
Exactly! And that's why it matters. Torque only tells half the story. It tells how hard you're pushing, but not how fast. Rpm only tells half the story. It tells how fast you're pushing, but not how hard.
Horsepower, since it's the product of torque and rpm, gives us one number that tells the whole story with respect to performance. It's the combination of how fast and how hard you're pushing. It can be made of pushing real hard, but doing it slowly, like a diesel, or it can be pushing not so hard, but real fast, like a gasser.
The horsepower number alone doesn't really say what the combination is, it just tells you the total. If you want to know the torque and rpm makeup, you have to look beyond the total.
BUT ... the exact makeup of the engine's horsepower, in terms of it's torque and rpm, are not particularly important for understanding the performance, because no matter what the makeup, we can easily convert it to the makeup we need at the rear wheels, by using the appropriate amount of gearing. Really, looking at the torque/rpm makeup of the horsepower just tells us things like how long it'll last.
Look, I understand you want really badly to believe that somehow your 300hp is stronger than someone else's 300hp because it has high torque and low rpm. It's a very common misconception and to some degree, the manufacturers encourage us to believe it. But it's just not true, if you really read and think about what I've said, that'll be clear. Nothing personal taken or implied.
[ 06-06-2002: Message edited by: ZFMax ]</p>
Hey Jumbo,
I have never seen one of those JD's crusing down the interstate with a load hitched up at 70 MPH. :D I don't think the engines on any 2500 or 3500 pickup have enough rotational mass to factor very heavily in the equation. I may be way off base but when I think of power like that I see a big mill wheel grinding grain or a ship engine.
Anyone else see it that way?
BMDMAX
ZFMax,
<<<Aaaaaaaaarrrrrrgggggghhhhh! I can't believe this topic has come back!>>>
I'm sorry!
Please understand that these debates really increase our understanding and are just plain fun to read! Thanks for your patience and great explanations!
Kevin
Jumbo Jet
06-06-2002, 20:34
The crank, rods, and flywheel of the 360 cubic inch diesel have a serious mass advantage over the 360 cubic inch gasser. Couple that with the higher compression ratio in the combustion cylinder and what do you have? The higher energy created by the diesel combustion transfers to the mass of the engine components creating higher horsepower at lower RPM.
You get an equivalency of energy by burning more gas in the gasser during the extra RPMs, give or take a few % due to other inefficiencies between gasoline and diesel. Therefore, you can create an equivalent horsepower, but typically at much higher RPMs. Nitrous, anyone?
There are some massive low rpm, high horsepower, high torque diesel engines out there. Transfer of energy to mass (horsepower) creates their high torque output!
3500HP 1900 RPM 10,200 ft.lbs. of torque for example. Burns a whole lot of fuel!! Weighs more than the front suspension an HD can handle.
The formula is constant.
If you know the torque number and the RPMs you can calculate horse power. And vice versa for whichever two numbers you know.
Horsepower depends on energy applied to mass.
How does the 'Juice' provide more torque? By increasing horsepower by creating more energy and transferring it to the mass of the cranks, rods, flywheel, etc. all at the same RPM before the 'Juice' was plugged in. Ignore timing, etc. Chips/boards like the 'Juice' can create more energy more efficiently. The key is that they create more energy.
Ignoring all the above and the other posts, my diesel truck out pulls and out performs my previous gassers and outweighs them by 2,500 lbs!
[ 06-06-2002: Message edited by: Jumbo Jet ]</p>
>>>>Transfer of energy to mass creates their high torque output!<<<<
No, you can't create torque by adding flywheel effect, sorry. All a flywheel can do is store energy, it can't create anything. It'd be cool if it could.
Sure, you get it spinning, and it's stored all that energy, and then you apply a load and it'll take longer to spin down because what's stored gets spent. But nothing's been created at all.
In the real world, it actually hurts usable torque, because as you try to accelerate, all that rotating mass also has to be spun up, and that takes some of the engine's torque, leaving less to accelerate the vehicle. If the flywheel was creating torque, the truck would accelerate faster. It's not, it's just taking away energy from the engine and putting it into storage.
[ 06-06-2002: Message edited by: ZFMax ]</p>
Jumbo Jet
06-06-2002, 21:50
Sorry ZFMax - if it wasn't for more energy being applied to mass, you COULD run that Lexus 300 HP V-8 in that Kenworth and pull that 80,000 load for a million miles. There is not a truck manufacturer out there willing to try that. Why?
Because they get 450HP at 1900 RPM by applying energy to mass. And I might say, a rotating mass!
Horsepower is created by applying energy to mass. Torque is created from horsepower.
SoMnDMAX
06-06-2002, 22:53
Jumbo Jet, ZF Max is right. Your kinda right, in a way. Yes there is energy being applied to a mass. But, not in the way your are describing it. The amount of mass affects the acceleration and the maintaining of that speed. High rotating mass = more of a maintained constant speed, but slower to get to speed, and also less ability to run at higher RPMs. Light rotating mass + fast accelerating, more subject to speed changes caused by load changes, and the ability to run more RPM.
The only reason a 360 diesel has more mass is because it has to be built stronger than a 360 gasser is to withstand the cyclical stresses applied by the violence of the diesel combustion process.
pinehill
06-06-2002, 23:19
As much as we'd like to think that we can understand all things intuitively in the physical world -- like relationships among things like mass, energy, power, force, torque, gearing and acceleration, it's easy to get off track unless you stick with the physics and math.
ZFMax has been entirely accurate in every statement he's made, and he's come up with some excellent examples to illustrate the concepts. I'm pretty sure that he could sit down with any of those who might dispute his arguments, and lay out the equations for them. I'm guessing that he's either an engineer, or has acquired a solid grounding in physics by some other career path.
pinehill
Engineer for 32 years (no, I don't mind the comments seen here occasionally about the stupid/impractical/unrealistic engineers who helped design our trucks) smile.gif
Kevin, thanks, it's gratifying to know someone's getting something out of all this typing.
Jumbo, if what you're saying was really true, why in the world would we need all this fancy engine technology? If we can add power by just adding flywheel effect, why don't we just put a Cox airplane engine in there with a *really* big flywheel and bring it up to 500hp and be done with it?
Fact is, flywheel effect saps up power, putting it into storage for later use. Doesn't add a thing, and in the real world, it slows you down because it bleeds off a portion of your power as you try to accelerate.
SoMnDmax has it right. Torque engines are built heavy duty because torque is twisting force. Rpm engines are built with lots of small, light parts because the engine isn't generating that much twisting force, the twisting force is generated downstream by the gear reduction.
Pinehill, thanks, and yes, I'm an engineer, although junior compared to you at only 24 years experience. Not that I was ever that good at physics, or remember much from those classes, but it's easy to remember things when they actually have relevance to you life, like this subject.
Jumbo Jet
06-07-2002, 11:31
ZFMax - The Cox Engine statment is exactly why I said what I said.
You cannot generate the necessary energy with the Cox engine to apply it to the mass (large flywheel) and maintain a reliable drivetrain..
The components of the diesel engine are designed with sufficient mass to absorb and transfer the diesel combustion (enery) and create more horsepower at lower RPM.
Why does the Durmax engine require more RPM to generate the same horsepower as the 2003 Cummins diesel engine?????? Shorter stroke, less mass.
Torque as you say is twisting power. That is where the rules of physics proves that the longer stroke engine can produce more torque at lower RPM.
Jumbo, longer strokes create more torque because they give the connecting rod more mechanical advantage on the crank, not because somehow the extra mass increases torque.
The rod journals are basically a lever; move it out (i.e. longer stroke) and you make the lever longer and the connecting rod has more leverage to twist the crank. It has nothing to do with any change in rotating mass. Rotating mass doesn't do anything except store power.
Amianthus
06-10-2002, 10:27
"Well, I'm pleased to see you clarifying your position, but the truth is diesels generally have a narrower powerband than gassers. I can prove that. But not now, you've left me too many other things to refute."
That's through bad wording on my part. Anyone who's met me knows that I know what I'm talking about. Even if I can't put it into words.
" If you want to ACCURATELY compare a diesel to a gasser, you have to consider that each NEEDS to be geared differently. Comparing them at the same gearing tells you nothing. The gasser would be going a whole lot faster with a whole lot less rear wheel torque available. "
Exactly my point. All things being the same (no gearing), the diesel will get to peak HP faster than the comparable gasser.
"Okay, yank your Duramax and replace it with a 1/2 hp, 1000rpm hand held drill motor geared 1000 to 1. Instead of that wimpy 520ft/lbs of torque, you'll have a whopping 2,626 ft/lbs of torque!
Problem is, it'll only turn 1 rpm. Yeah, you can pull a trailer, you'll just be pulling it *real* slow!"
Right, but you'll still have only 1/2 HP (assuming no losses, of course). My lawnmower could move a freight train with the right gearing, but it will still be the same 13 HP.(BTW, I drive a Cummins, not a Dmax. Not that it matters in this discussion)
"You see, when you're talking about performance, the rpm is every bit as important as the torque. That's why we talk horsepower. Horsepower is torque x rpm, it has BOTH of the important figures rolled into one."
I don't disagree. But HP can be ambiguous. Reason being that most people consider HP the end of all definitions of what an engine can do. HP alone doesn't tell you how much force you can generate at a given RPM. A tractor may have only 400 HP. But it will have 1600 ft-lbs of force. Now some believe that any 400 HP engine will do the job (and it will) but the gearing that could be required is outragious.
"Exactly! And that's why it matters. Torque only tells half the story. It tells how hard you're pushing, but not how fast. Rpm only tells half the story. It tells how fast you're pushing, but not how hard.
Horsepower, since it's the product of torque and rpm, gives us one number that tells the whole story with respect to performance. It's the combination of how fast and how hard you're pushing. It can be made of pushing real hard, but doing it slowly, like a diesel, or it can be pushing not so hard, but real fast, like a gasser.
The horsepower number alone doesn't really say what the combination is, it just tells you the total. If you want to know the torque and rpm makeup, you have to look beyond the total."
I shoulda looked at that before I made my last comment above. I agree with your above statement completely. Especially the part about looking beyond the total.
"BUT ... the exact makeup of the engine's horsepower, in terms of it's torque and rpm, are not particularly important for understanding the performance, because no matter what the makeup, we can easily convert it to the makeup we need at the rear wheels, by using the appropriate amount of gearing. Really, looking at the torque/rpm makeup of the horsepower just tells us things like how long it'll last."
Yup. I know that's not a really good qualifying statement on my part, but I can't think of anything to add to that.
"Look, I understand you want really badly to believe that somehow your 300hp is stronger than someone else's 300hp because it has high torque and low rpm. It's a very common misconception and to some degree, the manufacturers encourage us to believe it. But it's just not true, if you really read and think about what I've said, that'll be clear. Nothing personal taken or implied."
I am truly sorry if I gave that impression. That's not what I believe at all. Being that I understand the HP / torque relationship, I don't fall for the advertising crap that manufacturer's publish. I just believe that a high torque engine will get to it's peak HP faster than a low torque engine. And we could calculate that all day long.
Like I stated above, people that have met and know me, know that I am not stupid when it comes to this stuff. But I do have a tendancy to talk myself into a circle through the poor useage of grammar and vocabulary. And I want to say that I think that this shortcoming may be the reason why I gave the impression that I'm an idiot when it comes to HP.
I'm glad you guys tackled the rotational mass part also. When I first saw it brought up, I was gonna reply with a response, but it would just be re-stating what has already been said.
>>>>All things being the same (no gearing), the diesel will get to peak HP faster than the comparable gasser.<<<<
I still don't understand the point in comparing a diesel motor to a gasser at the same gearing. The gas motor is turning a lot more rpm. If you gear it the same as a diesel, it's geared for a whole lot higher speed. Of course it won't spin up as fast.
A comparison like that is functionally equivalent to taking a given truck and comparing it's acceleration in first gear to it's acceleration in third gear, from say a standing start. Sure, you gear something too tall, it accelerates slower, takes longer to reach peak hp, and ends up at a much higher speed. So?
To accurately compare performance, you gotta gear the diesel and the gasser for the same speed. It's the only way to do it.
In the real world, the driver of the gasser is running a shorter rear axle and/or is running a gear or two lower at any given speed, because his engine needs to be turning more rpm to make power.
>>>>HP alone doesn't tell you how much force you can generate at a given RPM.<<<<
Uh, that's PRECISELY what horsepower tells you.
Torque = (hp * 5252) / rpm
If you know hp and rpm, you know torque.
>>>>Now some believe that any 400 HP engine will do the job (and it will) but the gearing that could be required is outragious.<<<<
What's outrageous about gearing? I'm missing that point.
I think the outrageous thing about a high rpm/low torque motor in a tractor is that it'll wear out quickly. Applying more gear reduction is not the problem, that's just a function of putting more teeth on some gears and less on others.
>>>>I just believe that a high torque engine will get to it's peak HP faster than a low torque engine.<<<<
The load on the motor has nothing to do with the rate it spins up?
Or the load on the motor doesn't go down with deeper gearing?
Or deeper gearing can't be applied to a motor that has more rpm?
Look, I don't mean to pick on you. I'm a diesel fan. But it's because the motors last a long time and get terrific fuel mileage. Not because I think it spins up faster than a properly geared gasser.
Sure, it'd spin up faster than a gasser that's geared too tall, but I guess that doesn't mean much to me. I don't understand why it's important to you.
Amianthus
06-11-2002, 10:18
"I still don't understand the point in comparing a diesel motor to a gasser at the same gearing. The gas motor is turning a lot more rpm. If you gear it the same as a diesel, it's geared for a whole lot higher speed. Of course it won't spin up as fast."
The point is that a diesel, because of it's higher torque, makes power faster.
"In the real world, the driver of the gasser is running a shorter rear axle and/or is running a gear or two lower at any given speed, because his engine needs to be turning more rpm to make power."
With a driver who's experienced, I'd agree. But when have you seen a pickup truck with a gasser offered a different transmission than a diesel? Or a different rear end? You don't. They are both similarly equipped from the same list of options.
">>>>HP alone doesn't tell you how much force you can generate at a given RPM.<<<<
Uh, that's PRECISELY what horsepower tells you.
Torque = (hp * 5252) / rpm
If you know hp and rpm, you know torque."
And if you don't know rpm? Then what? Someone can post a number stating that the engine makes 700 HP. And we'd say that's alot. But what good is it if it needs to be spinning at 6000 RPM to get it? That's what I meant by the statement that HP is ambiguous. You don't see indy car engines in semi's for this reason. They make HP just the same as the diesel in a semi, but spins too fast and needs too much gearing to make it work.
"Look, I don't mean to pick on you. I'm a diesel fan. But it's because the motors last a long time and get terrific fuel mileage. Not because I think it spins up faster than a properly geared gasser."
No harm, no foul.
"Sure, it'd spin up faster than a gasser that's geared too tall, but I guess that doesn't mean much to me. I don't understand why it's important to you."
The reason why it's important is because the numbers a manufacturer publishes on a motor's performance are not gear enhanced (original point of the thread). Hence, the common misconception that a 300 HP gasser motor (motor only) will accelerate and hold a load as well as a 300 HP diesel (again, motor only) with the same load. With the diesel, you don't need the gearing advantage (or as much) because the force the engine makes (torque) is much higher (motor only). With all the typing above, I think we've already agreed on this.
>>>>And if you don't know rpm? Then what?<<<
Wait, your statement was "HP alone doesn't tell you how much force you can generate at a given RPM". Now you're saying you don't know rpm? Say what?
Personally I can't think of a BETTER description of horsepower than a number that tells you "how much force you can generate at a given RPM".
>>>>Hence, the common misconception that a 300 HP gasser motor (motor only) will accelerate and hold a load as well as a 300 HP diesel (again, motor only) with the same load.<<<<
That's a common misperception? I don't think so ... I think most people are smart enough to know that a gasser has to be turning more rpm to do it's pulling, and I think they also know that means it needs to be geared lower at any given speed. I have yet to see anyone try to argue that point.
A much more common misperception seems to be that the high torque/low rpm makeup of a diesel's power makes it somehow stronger than the low torque/high rpm makeup of a gasser's power, when geared for the same speed. That's patently false, although convincing some people of it seems next to impossible. There's quite an emotional attachment to the notion that somehow performance is described by the total combination of horsepower and torque, which of course is silly. Torque is already built-in to the horsepower figure.
>>>>With the diesel, you don't need the gearing advantage (or as much) because the force the engine makes (torque) is much higher (motor only).<<<<
Why is it a disadvantage of the gas motor to need deeper gearing? Why is that a bad thing?
Let's get to the crux of this thing. Near as I can tell, your point is that if you run a diesel and a gasser of the same horsepower in the same gear with the same rear axle, the diesel can pull a bigger load at a slower speed than the gasser. It can also accelerate faster to that lower speed (if the loads are the same). Right?
Agreed! It's horsepower is made of more torque (force) and less rpm (speed).
And do you agree that if you gear them for the same speed, which means the gasser has a shorter axle and/or you're in a lower gear, they can pull the same size load at the same speed and accelerate the same? You should anyway, if you truly understand hp, torque, rpm, and the effect of gear reduction.
Okay, so now we're not talking about the physics, we're talking about which of those comparisons is more meaningful, right?
And your point is that since they come with the same gear ratios, your scenario is more meaningful?
Tell me this ... if you've got a diesel and a gasser side by side, pointed up a hill, each pulling a trailer, identical axle ratios, identical automatics, both drivers with their right foot on the floor ... will the trannys be in the same gear? Or will the gasser's tranny know it needs to be in a lower gear and be twisting the engine tighter?
Same scenario, but with manual transmissions ... will the driver of the gasser choose the same gear as the driver of the diesel? Or will he put the transmission in a lower gear?
See what I'm getting at ... even if they COME with the same gearing (and you can get a shorter axle with a gasser), that doesn't mean the two trucks are IN the same gear under identical conditions. The gas truck will be operated in a lower gear and at a higher rpm than the diesel when it needs the rear wheel torque.
And when that happens, the torque advantage of the diesel disappears! The extra rpm of the gasser is turned into extra rear wheel torque. In fact, if it has the same horsepower and it's geared for the same speed, the torque at the rear wheels will be identical. The motors will spin up the same, too, so long as the horsepower they're making and the load on the rear wheels is the same!
Sorry, I just don't buy this whole notion that comparing them at the same gearing means anything. The motors run at very different speeds. You HAVE to gear them differently, to equalize their speeds, in order to properly compare their performance capabilities.
If you don't, you could just as easily argue that the gasser is superior because at the same gearing, it's going a whole lot faster! Who wants to drive slowly everywhere?
See how silly that is? The driver of the diesel will shift UP when he wants to go faster. Just like the driver of the gasser will shift DOWN when he wants to pull up a hill!
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