View Full Version : Allison 6th Gear Rumor
Anyone else heard a rumor that the Allison 1000 has a hidden 6th gear that is accessible with a software change? I heard it today. A guy at work knows someone who knows of a vendor that will provide the software for a price.
Seems to good to be true.
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'01 Silverado 2500HD Dmax/Allison Ext 4x4 SB - "I drive a 2500HD"
Plasticfantastic
11-28-2001, 20:08
Can he also get us tickets to the next Elvis concert? (just kidding http://www.62-65-dieselpage.com/ubb/biggrin.gif )
There IS some truth in this urban legend. It involves additional solenoids AND programming and has been discussed at length on this forum. (rumoured up to SEVEN speeds) It has also been stated that for this vehicle's hp,torque, and load capability, it has as many speeds as it needs to do the job.(what about the manual trucks?) A lot of owners already complain the Allison trans is too "busy". Would they want more gears?
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MEMBER #6086
2001 2500HD CC D/A Onyx/Tan
2001 Z06 Torch red (SOLD!)
2002 Z06 Torch red 405HP!
Where would this 6th gear fit in anyway? After 5th? Holy $#@! I think my truck goes fast enough! Back to reality Plasticfantastic
is correct, not only there would have to be a software update, you would need another set of solenids, clutches, etc. I think we have enough gears for the job.
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2001 2500HD LT Extended cab, D/A, Onyx Black, Graphite leather, 4x4, 295 BFG's on Eagle Alloys, MX7000 lightbar,lots of aluminum tread plate,
BOSS 9' snowplow, straight piped and lovin' it.....
2002 3500 Duramax/ZF6, LS, Summit white, 4x4
www.picturetrail.com/gallery/view?username=dslpowr (http://www.picturetrail.com/gallery/view?username=dslpowr)
1994 Chevrolet 2500 Silverado 4x4, Blown, injected 454, 9" Lift, PLAY TRUCK AND TOW TOY!!!
hunter98
11-28-2001, 23:07
It would be interesting. The resulting RPM's at a given speed with the factory tires for a .65 ratio OD (which is what I heard before that it is) would be the same as the .71 with the 285x75 or 255x85 tires (roughly).
With the 285x75R16 tires, and the .65 OD, you would be turning 1496 RPMS at 60 MPH, this compares to 1760 with 245 and the .71.
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
I'm going to pick-up my deep pan & stuff for my Allison on Friday. I'll pick the guy's brain a little bit about the 6th speed. My salesman said he heard the same rumor. Can you say.... 25MPG...?
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ColoMax
huntindog
11-29-2001, 02:21
I think it really needs a 6th gear, my milage drops 3 mpg. from 60 mph to 75 mph. I know that some of this is increased wind resistance but I bet most of it is rpm related. This thing has so much power that it could easily handle another gear. I can cruise up ANY hill in 5th gear as if it's a level road!
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Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
[This message has been edited by huntindog (edited 11-29-2001).]
Yes, the Allison is capable of six speeds. All the gearing is there. It would require factory changes to implement it but it is capable.
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded, Amsoil Air Filter, PS2K Propane, 22 Gal. LP Tank, Straight Piped, Allison Deep Pan, Transynd Syn ATF, SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level, VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's PICTURES (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
I'd be willing to bet you'd see little to no improvement in mileage. Yes, the motor will turn slower, but you'll be farther into the throttle to go a given speed than you would be with the shorter gearing. These things have a way of balancing each other out.
Look at it from the pure physics point of view. To go a given speed takes a given amount of power, and at a constant efficiency, that takes a given amount of fuel. Ultimately what decides whether it uses more or less fuel is whether the engine is more or less efficient at the new rpm. It's not a given that the engine is more efficient at a couple hundred rpm lower, and if it is, it's probably only a slight amount.
Aerodynamic drag goes up with the square of the speed increase. This is where the real problem with speed and fuel usage comes in.
huntindog
11-29-2001, 11:42
ZFMax, I agree to a point. If what you were saying were totaly correct then we should all be driving down the highway in 3rd or 4th gear. Point is we all know that it wouldn't work that way. If you reread my post you will notice that I did acknowledge the wind resistance factor, but the torque peak is at 1800 rpm and that is probably where it would be most efficient. At 75 It's turning about 2100 rpm. Thats a little high for a diesel. My 350 gas motor in my 73 blazer turns about the same rpm at 75.
"If what you were saying were totaly correct then we should all be driving down the highway in 3rd or 4th gear."
Hmm, apparently you didn't understand my post, because I said no such thing.
Let's examine your situation. If you're turning 2100rpm at 75mph, then you're turning 1680rpm at 60mph, right? (60/75) * 2100
So there's a loss in efficiency because you're running 300rpm over your torque peak instead of 120rpm under it, absolutely. No argument. Well, except that the dyno sheets seem to show a higher rpm for the torque peak than the 1800rpm GM claim. But we'll go with it.
Is this difference in efficiency the primary reason for your loss of 3mpg?
Consider this. At 75mph, you're going 25% faster than 60mph (75/60), but you have 56% more wind resistance ((75/60) squared). You've increased wind resistance 25% more than the change in speed alone would've changed it (1.56/1.25). I'd bet money that the change in efficiency of the motor is in the noise by comparison.
[This message has been edited by ZFMax (edited 11-29-2001).]
I'd love to see six speeds if it lowered the rpm difference between shifts.
Even better would be an infinately variable auto. No more up or downshifting. Just smooth changing.
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter
PS2K Propane, 22 Gal. LP Tank
Straight Piped
Allison Deep Pan, Transynd Syn ATF
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Headlight Booster Kit from Kennedy Diesel (http://www.kennedydiesel.com)
TRUCK PICTURES CLICK HERE (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
huntindog
11-29-2001, 14:23
Hmm, Who drives at 60 when the limits 75 on interstates? Try that and you'll get run over. Most people on this forum are obsessed with the idea of towing in overdrive. Its true, my truck will pull 10,000 easily in 5th. If thats the case then it could use a taller gear for running empty! This is the first truck I've ever had that could tow these weights in overdrive. I'm not questioning your math, but consider this If I have 520# torque at 1800 rpm, then why do I need to turn it tighter? It certainly doesn't take that much power to cruise empty. If it did then lessor powered trucks couldn't cruise at those speeds!
Brad Pelot
11-29-2001, 15:12
I think somewhere I read that the duramax makes over 500 lbs/ft at about 1500 rpm, although it's not the max; 1800, 500 lbs/ft. is a lot more than is needed to mantain 75 mph empty.
I think the most mpg benefit would be around 1500 rpm empty. After all, the little 5.3 liter gas engine in the half ton is around 1900 rpm at 75 mph, and it has plenty of power to propel itself down the road. I'm not sure what kind of torque numbers the 5.3 has at 1900 rpm, but it is surely a lot less than a Dmax at 1500 rpm.
True wind resistance is going to be a major factor with increased speed, but I think with lower rpm we could get at least 2 mpg better, say around 19 to 21. Just my opinion.
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Duramax x/cab 2500HD GMC 285 BFG's good truck
How about that 6th gear AND the option of 4.10's? Fiddle with that low 1st and reverse a little and with the 4.10's this would make for a sweet combo!
OH, I'm sorry, were talking about General Motors here...."Why don't we let Ford or Dodge do it first and let them make millions on it first, then we'll give it a try!
I think first they should let us enjoy all this torque and let us bog it a little more and let the engine do a little work instead of the Allison. Step by step we'll get what we want. We WANT the whole cow, but a glass of milk at a time is all were gonna get!
Sorry to rant!
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
"Its true, my truck will pull 10,000 easily in 5th. If thats the case then it could use a taller gear for running empty!"
Why? I don't understand the point.
"If I have 520# torque at 1800 rpm, then why do I need to turn it tighter? It certainly doesn't take that much power to cruise empty. If it did then lessor powered
trucks couldn't cruise at those speeds!"
Oh I see. You're equating rpm with power, saying that since you need less power to cruise empty, you should run less rpm, right?
But you're forgetting, you're not making 520ft/lbs when you're cruising empty, even if you're at 1800rpm. You've got a lot less load, so you're applying much less throttle to hold that speed. And that cuts the power.
Gear it taller and you'll have to apply more throttle to go a given speed and your mileage will come out about the same. Could even get worse. Depends on whether the engine is more or less efficient at the new rpm.
No, I argue that what you really want is what hoot said, keep the motor at the rpm where it's most efficient. Taller or shorter than that will hurt mileage.
I'll agree with you on one thing, engines are generally at peak efficiency somewhere near the rpm of the torque peak.
[This message has been edited by ZFMax (edited 11-29-2001).]
HD Hauling
11-29-2001, 16:00
Lawnboy,
Amen to your comment.You are right that GM is afraid to work the engine.Their afraid that they are going to Hurt the most powerful engine,what a Joke!!
What will you do with another gear when a person can't pull a 10000lb tailer down the road with out it shifting all the time!!
I'm getting between 20-23 mpg now and I'm happy with that compared to the 16-19 with the 5.3 I had before.Of course I'm not driving like a mad person either!
Have a Good Day
HD
Brad, it takes "X" amount of power to support "Y" amount of speed. Apply more power than that and it accelerates. That's physics, not my opinion.
So cruising at a given speed, you naturally hold the throttle in a position that limits the power to that level. You're not making what the dyno sheet says you're making at that rpm, because you don't have your right foot on the floor. The amount of power it *would* make if you had it wide open is irrelevant for understanding fuel efficiency.
Now gear it taller and go the same speed. The engine is turning less rpm. You still need "X" amount of power. You'll have to apply more throttle to get it, because you've got less rpm (power = torque x rpm, divided by a constant)
Why will this use less fuel?
I submit that it will only use less fuel if the engine is more efficient at the new rpm, i.e. it needs less fuel to produce "X" power.
Now IN GENERAL ... engines are most efficient at the rpm of their torque peak. There are a whole bunch of reasons behind this, but the basic idea is that a torque curve gives a good indication of the cylinder fill taking place.
[This message has been edited by ZFMax (edited 11-29-2001).]
I guess I don't have any room to talk, as none of my trucks even have 1 overdrive gear!
"Gear it taller and you'll have to apply more throttle to go a given speed and your mileage will come out about the same. Could even get worse. Depends on whether the engine is more or less efficient at the new rpm."
This engine has plenty of power for more gear. The slower the more fuel efficient. Nobody with an ALLISON has even begun to "WORK" this engine. And for those dually and chassis cab guys with the pizza cutters, a 6th (double overdrive) would be very beneficial. Perhaps make 6th gear locked out in tow/haul mode? Just for empty use.
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
The slower the more fuel efficient.
You're saying the greatest efficiency comes at the lowest rpm possible?
That statement is not accurate. If it was, car makers would gear all cars such that when we get up to speed and it shifts into overdrive, it drops to idle and we have to hold the throttle wide open to maintain our speed.
Truth is, it takes "X" amount of power to support a given speed. There's a wide range of rpm and throttle positions where that power level can be produced, and there's a point where maximum efficiency occurs, other rpms & throttle positions are less efficient. And the rpm of the torque peak is generally a pretty good indicator of the rpm side of it.
[This message has been edited by ZFMax (edited 11-29-2001).]
Wow, what has this turned into?
Get that truck running 75 mph and I'll give you a lawnmower engine that will maintain that trucks speed on the level! There is very little torque required to maintain highway speed. The slower that engine turns, the less fuel gets squirted into it. Simple.
I do understand where you are coming from with your theory, but you will not be into the throttle much more if any to simply maintain speed at that lower RPM.
Now if that engine was a Honda with a peak torque at 7000 RPM's, then yes your theory would hold true. But this Duramax makes more torque at idle than a Honda ever could!
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
"I do understand where you are coming from with your theory, but you will not be into the throttle much more if any to simply maintain speed at that lower RPM."
Now think this through ...
The amount of power it takes to maintain 75 sure as hell isn't going to change just because the rpm of the motor is something else, right? Hopefully nobody will argue that one.
But you're saying it'll use less fuel when geared taller. So, according to your claim, the more we lower rpm, the less fuel it takes to make a given power level? You're saying that an engine is always more efficient at lower rpms? And there's no limit?
What's your theory behind this claim?
Aren't engines designed for a peak efficiency at a certain rpm? For example, isn't valvetrain timing designed around a certain rpm? How about stroke?
Does boost make a diesel engine more efficient? Do we have more or less boost at idle than say, 1800rpm?
I think it might be useful here to examine what's really going on when rpm is lowered.
We all agree that for a given load, it takes a given amount of power to support a given amount of speed, regardless of the engine rpm, right? And I think (hope) everyone agrees that making more power than that will cause the vehicle to accelerate.
When you raise gearing and turn down rpm, power naturally drops, even if torque stays the same, because power = (torque x rpm)/5252.
Since the engine is turning fewer rpm, you're pumping fuel into the chamber less frequently, too. This seems to be what everyone's hanging their hat on.
But it ignores the fact that now you've got to replace the power you lost when the rpm dropped. Don't tell me it had more than it needed with the shorter gearing, either. If it did, it would've accelerated. if you're cruising, you've backed off the throttle to the point where it had just enough power to support that speed.
Back to the taller gearing scenario. To replace the power lost when rpm dropped, you have to raise torque. To raise torque, you have to put more fuel into the chamber. This is why you have to apply more throttle.
So all you've really accomplished is that you now are putting in more fuel less frequently than you were with the shorter gearing and more rpm.
Is this more efficient? Why?
The answer is not necessarily. In a diesel motor, more air is good. You basically can't over-air them the way you can a gas motor. More air makes the engine more efficient.
All engines, gas or diesel, are designed to take advantage of inertia in the intake tract. Basically, the later you close the intake valve, the more you're counting on inertia for cylinder fill, and the more you're shifting the point of maximum fill up in the powerband. The other three valve events have an effect as well, but the intake close point is the biggee. So valve timing has a very big effect on the rpm where we get the most fill.
The torque curve shows this. That's why engines tend to be most efficient at the rpm of the torque peak. The valve timing (and other effects like wave travel in the intake and exhaust) are delivering maximum fill at that point. And there is nothing restricting the air intake on a diesel the way there is on a gas motor.
Another thing people seem to be confused about, torque by itself means nothing without rpm. I can make a thousand foot pounds of torque with a handheld electric drill motor if I apply enough gear reduction. It wouldn't be turning very fast, though. Think of rpm as the rate of deposition. This is why horsepower was invented, something was needed that described both the torque and it's rate of deposition. It's basically torque x rpm. It's a much more meaningful number than torque itself. Ultimately, it describes how much torque will reach the rear wheels for a given ground speed.
I hope that clears up some things. I sense people arguing based on some kind of a gut feeling about how much extra throttle it would take, or just considering the slower pumping rate without considering that the torque also has to be raised to make the same power. This is all pure physics, nothing to really debate here at all.
Yes, I'm an engineer. You'll have to excuse me.
[This message has been edited by ZFMax (edited 11-29-2001).]
hunter98
11-29-2001, 18:30
My milage went up by about 5% (1 MPG) with 9% bigger tires. I do agree that it takes more throttle position at a given RPM to maintain a given speed, that is Physics. It is a matter of efficiency at a given RPM that will yield the milage. The greatest hurt to mileage at high speed driving is the drag. These trucks create alot of suction, (and lift kits make the suction even more).
Lets just consider the SWEET SPOT on the engine for my truck.
It was with the 245x75
54.6 MPH at 1600 RPM
61.3 MPH at 1800 RPM
68.2 MPH at 2000 RPM
Now with 255x85R16 it is
59.2 MPH at 1600 RPM
66.5 MPH at 1800 RPM
74.0 MPH at 2000 RPM
You will have to agree that the "SWEET SPOT" was raised by 5-6 MPH, up to the range that I normally drive in of 60-75 MPH, compared to 54-68 MPH. You drive 68 MPH on the interstate, you get run over, but at 75 your with the flow. Diesels are also very Finicky when it comes to RPM's and Mileage, this is why everyone is complaining about towing at 2800 RPMs or 2000 RPMs, the milage is over 50% better if you can get her to shift down. "BUT YOU ARE STILL GOING THE SAME SPEED"!
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
This is hopeless, I give up. Shouldn't have even stepped in here. Y'all go with what you believe, that's cool.
I'll leave you with this thought. Although aerodynamic drag goes up with the square of the speed increase, horsepower required goes up with the CUBE of the speed increase. For example, it takes 33% more power to go 10% faster (1.1 cubed = 1.33). That's not opinion, that's straight out of a physics textbook.
Why cubed instead of squared? Shouldn't it be the same as aerodynamic drag? Doesn't seem intuitive.
I could see this in the formulas, but it took me a long time to conceptualize why it's true. Once you hit on the solution it seems obvious.
I ain't telling!
I did a search and located an RV manufacturer that has the Allison T-1000 option that can be matched with a 215 HP 520ft-lb Cummins. The T-1000 is described as a 5 speed tranny with an overdrive (6 gears?).
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'01 Silverado 2500HD Dmax/Allison Ext 4x4 SB - "I drive a 2500HD"
huntindog
11-29-2001, 19:37
Zf,I'll agree with you on one thing, engines are generally at peak efficiency somewhere near the rpm of the torque peak.
That statement by you makes my case! I bet in a few years after GM has sold a few hundred thousand this way that a 6th gear will appear. We will be told by really smart engineers how this is more fuel efficient and all us uneducated people need to go out and buy a new truck to take advantage of this wonderful new option!
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Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
If I run through the rain will I be drier than if I walk through it, traveling the same distance?
Never mind.
Remember the Cadillac 4-6-8 engine? Well the same thing is coming out again by GM only this time they promise it will work. They say you only need four cylinders to maintain highway speeds.
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter
PS2K Propane, 22 Gal. LP Tank
Straight Piped
Allison Deep Pan, Transynd Syn ATF
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Headlight Booster Kit from Kennedy Diesel (http://www.kennedydiesel.com)
TRUCK PICTURES CLICK HERE (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
hunter98
11-29-2001, 20:36
How would the 8-6-4 work then, actually I think it is an 8/4, one entire bank shuts off. Wouldn't this be counter productive then. It is supposed to make the big trucks much more efficient. Also, if the argument was that it takes the exact amout of fuel to move the load was true. Then there wouldn't be a difference in economy among different engine sizes, say for example a 1500 pickup, compare the economy all with 5 speeds between the 4.3L, 5.7 and 7.4L engines. Big diffences. If engine size and RPM's weren't important, then we would all be driving 454 or 496, and wouldn't worry about having an OD at all, we would be able to climb up a 20% grade without downshifting while turning 3500 RPMS without missing a beat., the less throttle application would make up for the difference. http://www.62-65-dieselpage.com/ubb/wink.gif Now lets have some sense here, this is the same reason why you have different ratio rear ends from 3.08 to 4.56 to compensate for the use, also why the lowest ration is 3.73 that you see on a 2wd 1500, because even at that you are hurting milage. The OD transmissions are one of the biggest advancements in fuel economy ever done to pickups.
I AGREE with the SPEED KILLS MILAGE ARUMENT, but the speed isn't the only factor that sets how much fuel is consumed, RPMS, peak efficiency, torque curves, aerodynamics, weight, grade, tire pressure, ect.
Hunter
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2 http://www.62-65-dieselpage.com/ubb/biggrin.gif http://www.62-65-dieselpage.com/ubb/biggrin.gif 2 GMC SLE Ext Cab SB 4x4
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
[This message has been edited by hunter98 (edited 11-29-2001).]
huntindog said:
"At 75 It's turning about 2100 rpm. Thats a little high for a diesel."
So, Mr. ZF-Engineer, what would his RPM's be with a 6th gear overdrive ratio of .65? A LOT closer to the engines peak torque/efficiency range. And a LOT slower RPM's, saving a LOT more fuel. Nothings going faster, nothings catching more "squared" air drag. Its just spinning a SLOWER RPM. This in itself WILL save fuel. Maybe not in your physics textbook, but in the real world it WILL. With todays speed limits, traffic often travels around 80 mph and at that point, this truck is just too busy, and that double overdrive would correct this AND save fuel.
I'm done now http://www.62-65-dieselpage.com/ubb/rolleyes.gif
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
Maybe GM is waiting for the new ford 5spd and will quickly offer the 6spd to give an edge right back to GM. This sounds good but who knows.
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1998 6.5 2500 4X4 Ex-cab Short bed 4.10 gears 4in BD ex
hunter98
11-29-2001, 21:48
Actually, the RPMS with stock tires at 75 MPH should be 2201, with 265x75 would be 2119, with 285x75 would be 2043 RPMs in the .71 OD. With the .65 OD, the RPM's would be 2015, 1940, and 1870 Respectively. Now figuring a high speed run at 85 MPH
With .71/.65
245=2494/2283
265=2401/2198
285=2315/2120
As you can see, this would bring down the RPM's about 200 RPMs at 85 MPH.
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
ChevysRus
11-29-2001, 23:39
You all are making my head hurt too much. LOL I am still trying to understand that "get her up to 60 and drop it into first a couple of times to re-train the transmission" thing. Man if I beat my dog to "re-train" it, I can go to jail, not to mention getting a dog bite on my butt!
All I know for sure is in my 1939 Chevy I have a 350 S/B and with the Turbo 350 trans and 3:51 gears, I was turning 3000 RPM at 60MPH. Great for the 1/4 mile, but really, really sucks on a 900 mile trip. My fuel mileage was about 10-12 mpg. So I go out and get a 700R4 with "overdrive". Now I can cruise at 60 mph and only turn 1800 RPM. My mileage is now 15-18 MPG. The "overdrive" is .70. Tires are the same under both Transmissions (by the way they are the biggest I could get to fit the wheel well).
I also confess, I don't (normally) drive (normally) 60, (you guys figure out where the normally should be). LOL
SOOOOOO, if an "overdrive" can produce those kind of results, I would think an extra gear in the DMAX would be a "good thing" and if someone can figure out how to do it, I will buy it. Hell I will buy anything, let's face it. I am going over to the Allison place next week to get the deep pan and that fluid I can't spell (see I said I would buy anything for my truck) and I will ask them if they have done any "Mods" to get a 6th gear out of the 1000. IF they crack up laughing at me then I will know the answer and let you know. If it can be done, I'll see if they will do it while I wait! Can't wait to get back to my Chevy dealer and ask for the software upgrade for my 6th gear! Man I can just see the look on their faces. LOL
Let's all play nice now
huntindog
11-30-2001, 02:40
I'm thrilled that a few people have stepped up to help me debate with an engineer type! I always have a tough time with intellectuals,( while I'm trying to figure out what they're saying, I forget what I was going to say) LOL. Anyway I was looking in my brochure and noticed that the 8.1 has 340 hp at 4200 rpm and 455 torque at 3200 rpm. Soooo, according to my engineer friend an 8.1 shouldn,t use 5th gear at all! 4th gear would put the 8.1 right at the torque peak and the fuel savings would come from less throttle input! Any 8.1 owners out there want to try this and get back to us with a report? FDLMAO
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Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
[This message has been edited by huntindog (edited 11-30-2001).]
ZFMAX are you still out there?
He must be real busy double clutchin' trying to figure out which physics book he needs to contradict the 1939 Chevy with a 350/350/3.50 vs. 700R4 information!!
I will say one thing, the average truck buyer who installs larger tires and really dosen't take long trips will never have a use for this 6th gear. But for those with stock tires that travel all over the country at highway speeds, this would be the hot ticket to 20+ mpg at 75-80 mph. If they could do it, it would have to be something that would stay in that gear, hold it, not jumping back to 5th everytime the wind blew crooked.
OK, OK, I know I said I was done now, but, with all my supporters popping up, I just had a little more to say!
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
I ain't gonna argue with ya, but I do have some questions ...
Its just spinning a SLOWER RPM. This in itself WILL save fuel.
You're just making a claim. Just saying something doesn't make it so. What's your understanding behind why less rpm always equals less fuel consumption and throttle position has nothing to do with it? Just because you know? Is that all you've got?
Fundamental question for ya ... Why does the engine need less fuel to produce the same power when it's spinning slower?
I'll give you one answer to that ... frictional losses in both the engine and tranny are lower. But what percentage of the load on the motor is it? And where does it crossover the loss in breathing efficiency?
More questions ... if what you're saying is true, why doesn't GM make the overdrive .5? Or .4? If taller is always more efficient, why not find the point where it will support 75mph unloaded with your right foot on the floor, and put the overdrive there? Or 95mph, since they have a limiter there anyway?
Or ... could it be ... is it possible ... that *perhaps* it's possible to go too far? Is it possible that you reach a point where you're having to apply so much throttle to maintain your speed that you actually end up with less fuel efficiency?
Hmm, what a concept!
Where is that point? Idle?
Why is it where you believe it is?
Think it through, man. Present a cohesive argument. Don't just make claims you can't substantiate.
[This message has been edited by ZFMax (edited 11-30-2001).]
I guess were steppin' it up a notch? BAM! http://www.62-65-dieselpage.com/ubb/eek.gif
[i]Or ... could it be ... is it possible ... that *perhaps* it's possible to go too far? Is it possible that you reach a point where you're having to apply so much throttle to maintain your speed that you actually end up with less fuel efficiency?[i/]
We are talking about a DURAMAX here, aren't we?
This engine, with its flat torque range, WILL HAVE TO ACHIEVE BETTER MILAGE with 211 LESS RPM. Thats the end of my argument. I dont need proof.
I do understand where you are coming from with your theory, but you will not be into the throttle much more, if ANY, to simply maintain that same speed at that lower RPM.
I never mentioned .5 or .4 overdrive ratio's, and if it makes you feel better, that is about where I would draw the line in diminishing returns.
[i]Think it through, man. Present a cohesive argument. Don't just make claims you can't substantiate.[i/]
I dont need to think it through, "man". Your the one doing all the thinking here Mr. Engineer. http://www.62-65-dieselpage.com/ubb/smile.gif
I dont feel obligated to substantiate any claims. I just posted what "I" feel is correct in this little head of mine. Where exactly is your "real world proof"? Maybe if you weren't lugging around all those engineering books, you'd get better milage! http://www.62-65-dieselpage.com/ubb/biggrin.gif
Boy this is starting to look like something off of TDR or FD.com. eekks!
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
"you will not be into the throttle much more, if ANY, to simply maintain that same speed at that lower RPM."
Okay, now we're getting somewhere ...
Would you agree that it takes the same amount of power to support a given speed, regardless of the rpm of the motor?
If you buy that, do you agree that lowering the rpm without increasing torque reduces power? Remember, power=(torque*rpm)/5252
If you buy that, how do you go about getting more torque out the motor at the new lower rpm? You're saying it can be done without feeding more fuel into it?
Lawnboy,
It's a very complicated subject. Even the best engineers don't have it 100% figured out so how can we?
Just some of the things involved are....
What goes on in the combustion chamber, eg. fuel burn, air movement (different at different rpms).
Intake and exhaust variables.
Heating and cooling of gasses at different rpms and loads flowing through the entire system.
Friction
And tons more. It's difficult to simplify it.
Usually, a given amount of work requires the same amount of input. Whether you are operating at 1800 or 2000 or 3000 there still is a set amount of power required to do the same mph. The rpms are the differences in these arguements but you need to factor in the variables given above in this post.
If a piston reciprocates 50% more times at the same mph, I would expect less efficiency mainly due to the extra friction/time but you just can't make that assumption.
Friction of the moving parts at a higher rpm is multiplied. Not that there is more friction at any given component but if a piston moves up and down twice compared to once in the same time period, the first would have been "dragging" a longer distance (not sure about that one having much effect). Also the piston changes directions twice in the same time period.
Oh well, I tried....
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter
PS2K Propane, 22 Gal. LP Tank
Straight Piped
Allison Deep Pan, Transynd Syn ATF
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Headlight Booster Kit from Kennedy Diesel (http://www.kennedydiesel.com)
TRUCK PICTURES CLICK HERE (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
The minuscule amount of more fuel required is nothing compared to the RPM decrease improvement. These parameters are not scaled together. We are talking about 211 RPM here NOT a whole heck of a lot, but enough to cancel the effects (minor) of more fuel to maintain said speed. If your theories are correct, then why even have an overdrive??? Think about that! I do agree that there is a point of diminishing return. It's where that "point" is that we are debating about. I'm saying we can go with slightly more OD (on a transmission that has this capability) and realize a significant MPG increase. Your saying it will flat out decrease my MPG. Neither of us know EXACTLY were this point is, BUT.... I can wholeheartedly estimate that it isn't at a .65 OD ratio with this engine!
Come on other guys...back me up!
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
huntindog
11-30-2001, 10:44
Hey ZF think about this; On a gas motor overdrives work. I don't think even you can dispute it. But a gas motor has peak hp and torque in the 3000 to 4500 rpm range. Soooo when using overdrive in these situations we are moving away from the powerband. We are talking diesel here and moving towards the powerband. It should work even better than on a gas motor! Thats all for the next ten days I'm goin huntin! I'll check when I get back and see If ZF is through gnashing his teeth. LOL
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Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
77TransAm
11-30-2001, 10:52
Has anyone looked into any fuel economy figures for the bigger Allison electronic transmissions (ie the World Transmissions) that use the same planetary arrangement as the 1000s? The WT is generally used as a six speed, but some fleets choose to use it as a five speed. That difference should provide some real world numbers for a diesel truck with an Allison and five vs. six speeds.
"The minuscule amount of more fuel required is nothing compared to the RPM decrease improvement. These parameters are not scaled together."
Not scaled together? Are you sure?
Do you accept that power=(torqueXrpm)/5252?
Do you agree that torque and rpm have the same weighting in that formula?
If you decrease rpm by some amount, say 10%, don't you have to then increase torque by 10% to get back to the same power level?
"I do agree that there is a point of diminishing return. It's where that "point" is that we are debating about."
Where do you think it is? What rpm? Why do you think it's there?
"I'm saying we can go with slightly more OD (on a transmission that has this capability) and realize a significant MPG increase. Your saying it will flat out decrease my MPG."
When did I say that? Doesn't it have something to do with the speed you're going, and the resultant rpm? Is it possible that going taller in the gearing will help mileage at some speeds and hurt it at others?
Huntin: I agree completely.
ChevysRus
11-30-2001, 12:27
Let's jump to the concept cars that the environmentalist are trying to push us towards. These are basically low HP and low RPM fuel efficient machines (forget batteries for now). They accomplish the efficiencies mainly through 'GEARING". Once up to speed (whatever it is) they try for maximum wheel RPM and lowest engine RPM. They are very efficient getting 80 + MPG (ignore weight, aerodynamics etc. for now). just the concept highest wheel rpm at lowest engine RPM = Greatest Efficiency
Would you want to pull out in traffic in one of these, hell no, it would take you a hour to get up to speed if there was a downhill and no uphill. So my point is that there is a trade off in performance with improved efficiency. That has to be a no brainer for anyone. GM has decided that the current DMAX/Allison combo gives the best performance across all driving situations and the efficiency that goes with this combo. Now if you never have to pop into traffic or pass a 18 wheeler or climb steep grades pulling 15K behind you, then they can build a more efficient combo giving up some performance in the process. If I am running 2000 RPM at 70 MPH on a flat road, empty and if I had another gear to go to in this situation that would maintain 70 at say 1800 RPM, I have to believe I will pick up a few MPG in the process. Now maybe I can't speed up in this new gear as fast or get into it under 50 or 60 (lug the engine), but once up to speed (70) at 2000 RPM, it should have no negative impact and slight positive impact on MPG, by dropping the RPM (lower RPM = less fuel consumption)(also less available power), but the lost power is not needed under this condition). I understand I have to give up the full performance that a 5th gear would offer in a situation where I needed to accelerate, but I can always downshift to 5th, (sounds good to say downshift to 5th).
OK so there is probably no end to this discussion as we are dealing with perception vs. theory. By the way perception rules the world, right or wrong. Wars are being fought over differences in perception.
So I volunteer (listen up you Allison guys) to submit my truck to the experiment, give me the 6th gear for 25 years to use and I will file periodic reports on the performance and impact on MPG.
Have Fun, Live Long, Prosper and Get Naked!
ZFMax,
Why do you so FIRMLY insist, without any reasonable doubt, that the Allison in the GM trucks with a 3.73:1 rear gear and the Duramax cant benefit (+mpg) from a .65 OD ratio?!
What about ALL the 6.5's out there with 3.42:1 gears??? They DO for a FACT get BETTER fuel milage than a corresponding and otherwise identical 3.73:1 geared truck.
And how can you agree completely with huntindog, (who is saying the EXACT same thing as me), and not with me?
Bottom line. These trucks (almost all trucks for that matter) benefit from OD. How much is too much....????? Is .65 "TOO" much....????? You think it is, I think it isn't.
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Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
hunter98
11-30-2001, 13:06
I would think that the Duramax 3.73 would benefit with the .65. I also think that the 8100 should be offered with the .65 OD 6 speed. But the truck should only be offered with the 4.10 rear end. The .65 OD would offset the 4.10 rear end back to the previous 3.73/.71 setup. This would allow for the most towing power, low end power, ect. You can go too far on a big truck with a gas engine at dropping RPM's. The drop, especially with bigger tires is not needed as much on the 8100. But with the Duramax, it would help alot on the highway.
All of this, without reducing towing or low end power http://www.62-65-dieselpage.com/ubb/wink.gif
Hunter
PS, have a nice weekend, I got deer to hunt!
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2 :D :D 2 GMC SLE Ext Cab SB 4x4
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
"Why do you so FIRMLY insist, without any reasonable doubt, that the Allison in the GM trucks with a 3.73:1 rear gear and the Duramax cant benefit (+mpg) from a .65 OD ratio?!"
I said that? When? Where?
Or did I say lowering rpm does not necessarily equal better fuel efficiency? And you extrapolated the rest?
FWIW, I'd bet money that my highway mileage would improve with a .65 OD. At the highway speeds I drive (75-80), my engine is turning faster than the point where it's most efficient. A .65 OD would move it in the right direction (that wouldn't be true at 60, though).
However, I'd also bet that the difference in efficiency between my new and old rpm would be slight. The mileage improvement isn't going to track the rpm reduction, as many people seem to think. Spinning slower, I'll have to apply correspondingly more throttle to make up the lost power and support the same speed. This will offset much of the gain I got by reducing the rpm. Like I said in my first post, these things have a way of balancing each other out.
Bottom line, there's only so much energy in the fuel, gearing taller doesn't change that fact. All it would do is put the engine at a point where it's slightly more efficient at converting the fuel into power. Assuming you're going a speed that puts the new rpm closer to the point of maximum efficiency.
I'm still trying to understand why you think you can lower rpm and make the same power without applying "ANY" more throttle. This is where our disagreement lies.
[This message has been edited by ZFMax (edited 11-30-2001).]
Than how do you explain the large mileage drop between 55 and 75?
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter
PS2K Propane, 22 Gal. LP Tank
Straight Piped
Allison Deep Pan, Transynd Syn ATF
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Headlight Booster Kit from Kennedy Diesel (http://www.kennedydiesel.com)
TRUCK PICTURES CLICK HERE (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
cantravel
11-30-2001, 14:31
Very interesting!
Another example of an intelligent,technical and doggedly persistent discourse on a subject not all that easy to understand.
Sometimes, things defy our intuitive logic.
01 Chev K3500 LT D/A Crew LBx
Diesel Page Member #40
Idle_Chatter
11-30-2001, 14:58
Hoot, I've been trying to stay out of this one, but I just couldn't help myself! I noticed on my 6.5TD Tahoe (especially after I put in an EGT and boost gauge) that there were several "sweet spots" or very efficient rpm ranges where performance and economy really changed dramatically! For instance, in the Tahoe on cruise on the highway, 68 mph was about 2100 rpm and the engine held about 4-1/2 to 5 pounds of boost. But if I pushed it up to 75 mph and 2250 rpm, boost would drop off to nearly nothing (meaning to me that the engine was producing *more* horsepower than previously without having to boost!) and would get 2 or 3 mpg better economy!! There was another sweet spot down around 62 mph and 1850 rpm. So I would routinely run on "high and low cruise" 2250 rpm and 75 mph on the open road, 1850 and 62 mph in towns and posted 55s!
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Tom Ashley
2001 DuraMax/Allison
2500HD Silverado LT
Lt Pewter/Graphite Lthr
Ext Cab/Shrt Box/4x4
Line-X/Century Ultra Cap
Amsoil 2-Stage Aircleaner
"Than how do you explain the large mileage drop between 55 and 75?"
Ah, at last we come full circle! We went over this!
Aerodynamic drag goes up with the square of the speed increase. When you go from 55mph to 75mph, you increase speed 36%. BUT ... you increase aerodynamic drag 86%!
This is the fundamental reason your mileage drops, not the change in rpm between those two speeds.
Thank you for bringing that up again, because the intent of my first post was to point this out, and somehow I got dragged into this long discussion of engine rpm's and efficiency.
Has nobody figured out yet why power required goes up with the CUBE of the speed increase, yet aerodynamic drag only goes up with the square?
In that example ... 55mph to 75mph ... drag goes up 86%, but horsepower required actually goes up 154%! Very non-intuitive (at least it was to me), but true.
[This message has been edited by ZFMax (edited 11-30-2001).]
Here's a thought. Get yourselves an OBDII scanner and collect fuel rate (in^3)in real time for both 55mph and 75mph runs. The first test will be at 75mph and no wind. The next test will be at a speed=75mph-Xmph, where X is roughly the steady headwind of the day. This should provide similar wind drag for the 2 test drives so the results will only be a function of engine RPM (roughly!).
Be sure to post the results! http://www.62-65-dieselpage.com/ubb/smile.gif
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'01 Silverado 2500HD Dmax/Allison Ext 4x4 SB - "I drive a 2500HD"
[This message has been edited by AzKevin (edited 11-30-2001).]
[This message has been edited by AzKevin (edited 11-30-2001).]
huntindog you are so right about towing in 4th with an 8.1, the trouble is how do you keep it from shifting into 5th??????????? dave p
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2001 L
The problem with all this theory is it's to simplistic, there is a multitude of factors affecting fuel economy. The other problem is that theories to often fall apart when they meet the real world, a theory that stands up to imperical evidence may be accepted as fact.
Let's deal with some real world examples. How many of you that put on larger tires improved your fuel economy? The problem here is what works for you may not work for me; variations in trucks, driving styles and applications will have an affect on the outcome.
If someone in the Houston area can give me information on obtaining one of the warranty replaced two piece driveshafts, I will install it along with my Gearvendor overdrive and use my crewcab short bed to settle this.I currently get about 17.5MPG unloaded in town.I think I can beat 20MPG with the GV unit.I know it will on the interstate.
Seriously, I do need another shaft to experiment with. I have been wanting to do this for sometime and can't locate a shaft to modify.
gv
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With the TSB (dual driveshaft replacement) dealers should have oodles laying around. Unless of course they return them to the factory.
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'01 Silverado 2500HD Dmax/Allison Ext 4x4 SB - "I drive a 2500HD"
a64pilot
12-03-2001, 18:08
FUZZMAX,
I don't think that you will get what you want from a dealer. I would think that these shafts would be considered defective from the legal stand point. If they weren't defective why would GM have replaced them, I can hear a lawer saying that now. The libility would be enormous. Any how way back in my drag racing days it was quite common to have a local machine shop make a custom driveshaft. I don't remember it being very expensive either.
I would like to hear about your results. I am one of the guys that think that you will experience better milage. At least unloaded and on the highway.
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2001 C3500 LT Charcoal Grey
CC/Longbed Putco boss boards,
virtual grill,mudflaps,sill protectors Rhino liner,
bug deflector. Looking into Boost/EGT gague
Absolutely fascinating discussion........but somewhat off the point.
All AzKevin wanted to know was is there a "hidden" 6th gear. The truth is that there is! http://www.62-65-dieselpage.com/ubb/smile.gif
The 1000 Series was designed with the same gear/clutch scheme as it's big brothers the MDs and HDs, and they have six forward gears. It can handle a 6th gear with the addition of some HARDWARE (valve body, valve, solenoid, etc), and changes to the SOFTWARE to address the additional shifts. 6th gear would manifest itself as a second (larger) overdrive, and it's ratio would be .61 to 1 (.6143 to 1 for those tending towards anal retentiveness). Currently the 1000 Series has 5 forward gears, with 5th being overdrive at .71 to 1.
It's anybodies guess if and when GM will ever add this to the HD Pickups!
I have NO intention of enjoining the debate regarding whether or not you need/want the additional Overdrive! http://www.62-65-dieselpage.com/ubb/wink.gif
Now that makes me think about 4.10 gears and six speeds.
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter
PS2K Propane, 22 Gal. LP Tank
Straight Piped
Allison Deep Pan, Transynd Syn ATF
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Headlight Booster Kit from Kennedy Diesel (http://www.kennedydiesel.com)
TRUCK PICTURES CLICK HERE (http://onramp.uscom.com/~hoot/cars/duramax/gmc)
1994 K1500 Blazer 350 Loaded, Flowmaster duals
hunter98
12-04-2001, 10:22
HMMM,
with the ratio big al gave me, I made some calcultations. Factory setup is 2201 RPM at 75 MPH in .71. With 285, the .61 and a 4.56 Rear end, you would be at 2161 at 75 MPH. Only real disadvantage would be a REALLY LOW REVERSE! Of course, it is already so low that you wouldn't loose but 2-3 mph anyways. The 2201 would drop to 1904 with the factory setup (tires, rear, ect). With 285 it would drop from 2043 to 1767. With 285 and 4.10, it would drop from 2245, to 1943.
I personally think that the 4.10 with the 285 tires and the .6143 6th speed (FROM THE FACTORY http://www.62-65-dieselpage.com/ubb/wink.gif ) would be great! 1943 RPMS would work good for milage at 75 MPH, the 2245 is actually a little bit higher than origional in 5th, and would promote a little bit better towing power, plus the 4.10 in the lower gears would more than makeup for what is lost by the 285 tires in the lower gears, each gear would have about 2% more mechanical leverage, instead of being down 8%.
THIS WOULD BE THE ULTIMATE SETUP
Hunter
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2 http://www.62-65-dieselpage.com/ubb/biggrin.gif http://www.62-65-dieselpage.com/ubb/biggrin.gif 2 GMC SLE Ext Cab SB 4x4
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
[This message has been edited by hunter98 (edited 12-04-2001).]
SoMnDMAX
12-04-2001, 11:34
But, to make it all worth while, there would have to be some sort of manual control of the 6th gear, just to prevent the downshifting problems again.
Hey Big Al, maybe you guys could come up with a retro kit and sell it thru GM Perf Parts???? Or you could just list the necessary P/N's.. http://www.62-65-dieselpage.com/ubb/biggrin.gif
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PICTURES (http://www.picturetrail.com/somndmax)
2001 Chevy 2500HD Duramax, Allison, Ext. Cab SB Forest Green,
285's and Centerline's put away till spring... Now equipped with Goodyear Workhorse Extra Grips, 265/75-16 on the PYO's
Autometer Boost and EGT gauges, Amsoil air filter, Access Tonneau, Luverne Stainless boards, JL Audio 12" sub, Phoenix Gold amp, Clarion door speakers...
Kennedy Diesel Headlight Harness
4" Kennedy Diesel exhaust installed!!
Power Play Module from Kennedy Diesel (http://www.kennedydiesel.com) Soon to be complemented by a 120HP Module
Diesel Page member #6184
SoMnDMAX,
Whatever are you talking about?!?!?!? http://www.62-65-dieselpage.com/ubb/biggrin.gif
My G2 sources say the parts don't exist in any fashion, but they also say the notion is being kicked around. The performance debate which has raged in this thread is certainly going on somewhere in the bowels of GM Engineering. My experience within the Medium Duty business tells me unless there is some interest on the part of an OEM customer, it ain't gonna happen!
Of course, that doesn't stop some aftermarket guy from jumping in; but even he has to have some belief he can sell enough kits to cover his investment and a little pocket change to boot. http://www.62-65-dieselpage.com/ubb/wink.gif
Gut feel.............don't look for a 6th gear anytime in the near future!
a64pilot
12-04-2001, 14:12
BigAl,
Probably only about 20% of us understand G2. You have to remember you are addressing a primarly civilian crowd. http://www.62-65-dieselpage.com/ubb/biggrin.gif
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2001 C3500 LT Charcoal Grey
CC/Longbed Putco boss boards,
virtual grill,mudflaps,sill protectors Rhino liner,
bug deflector. Looking into Boost/EGT gague
Oops, guess I showed my age on that one, huh? http://www.62-65-dieselpage.com/ubb/frown.gif
For those of you who don't know, G2 is military shorthand for "Intelligence"...........as in information, usually obtained via clandestine activities.
Do I need to define "clandestine"??? (it means under cover, quietly, secretly, like those spooks over in Afghanistan are doing trying to locate Mr. Bin Laden!)
ChevysRus
12-14-2001, 17:49
At the risk of opening up "old wounds" an update and maybe the final answer.
I was over at my local Allison dealer today to pick up some back ordered parts (deep pan and pickup screen) and just for the heck of it I asked them about how to get all the old DEX out when adding the TranSynd (hurrah finally got right spelling). Well the counter guy gave me the same old standard answer, "you will have to ask the shop guy and he's not here right now". Just then the owner of the dealership and an Allison rep walked by and overheard the conversation.
So the owner who appears very knowledgeable (proof later) and the Allison rep say to just drain the pan and add new fluid to get a 70% mix of tranSynd. He said in a few weeks if I check the trans fluid, the color will look like baby S..T!, but it is fine. The color change is the old DEX breaking down. Do the next transSynd change at 25K and then go 100K. He also stressed following big points:
1. Never, never power flush an Allison trans. It has been discovered that this process for some reason (pressure) blows the little "O" rings and some of the rubber seals inside the trans and renders it useless.
2. Absolutely change the spin on filter at 5K (as Big Al has told us), as the majority of filings and clutch material shows up in the first 5K. After that it is normal changes per manual.
3. I asked about disconnecting the cooler line and dumping fluid until the color changes to get more DEX out. He said yes you can do that, but you can never get it all out of the nooks and crannies (his words) and completely out of the converter. The second change should flush most of it out as the TranSynd will wash the DEX away.
4. After the second change you can go 100K. This is the good part, they told me that next year TranSynd would announce 150K is good to go after the second change.
So having the opportunity and being the pushing guy I am, I thanked them and said," by the way, what do I have to do to get you guys to add the sixth gear"? They both looked at me and said, just add the solenoid!
Then they got serious and explained why the sixth gear was not available and here it is.......
Apparently, the U-joints and driveline can not handle the additional velocity generated by the sixth gear overdrive. He said if the limiter was set to 60 MPH, maybe the RPM of the engine and driveline could hold up, but that since people can't drive this way and want to go faster, the U-joints would be flying out the ass end of the truck. In order to get the sixth gear operational the entire driveline has to be re-designed and beefed way up to handle the velocity.
This is probably the best explanation I have heard and it will be interesting to get SteveO and Big Al's comments along with everyone else's. The guy went on to say, that this is the reason they had to step down the Allison in the big trucks to just 4 gears as even the big rigs could not hold the velocity of 5th gear much less 6th gear and even the tires are bigger too.
Well I expect this to take on a lively debate. so have at it guys!
Dinkie Diesel
12-14-2001, 19:06
Okay I'll bite! Let's see.....they are saying that the u-joints would fly out the ass end of the truck if it were allowed the additional overdrive gear due to velocity. Balderdash! Would adding the additional overdrive allow the current governed speed of ~98 mph to be over-ridden? Using Hunter98's numbers above, I concluded that if the governor were not implemented you would get approximately 109 MPH at an orange line of 3200 engine rpm. If the .61 OD were allowed you could get 126 MPH at 3200 rpm. The driveshaft would still only be turning 5245 rpm at 126 MPH. Anything that is 4 or 5 inches in diameter (the driveshaft or yokes) and can't spin at 5245 rpm without flying apart probably can't spin at 4048 to do 98 MPH in 5th either. Somebody is full of $hit or I have a lot to learn.
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74743.2745@compuserve.com
2001 K2500 Crew Cab LT Duramax / Allison 4x4
huntindog
12-14-2001, 20:04
Chevysrus, This is crazy! The u joints don't care what gearing the tranny has. A u joint only goes as fast as the pinion gear and is a function of road speed. If the speed is still limited to 98 mph, then u joint velocity would be the same. I see no reason to go faster, That's not what trucks are for!
------------------
Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
slapshot44
12-14-2001, 21:37
Ditto to what Huntindog says. The driveline's (and u-joints') rate of rotation is directly linked to the rate of rotation of the tires. 70 mph is 70 mph, and the driveline's rotational rate is constant, no matter what gear the tranny is in.
Changing differential gear ratios will change the rotational rate for any given speed, but adding additional overdrive in the tranny just lowers engine rpm for any given vehicle speed. If there were no speed limiter on our trucks, the over-rotation scenario would make sense, the faster you go, the higher the rotational speed is, and is probably one of the prime reasons for having the speed limiter in the first place. But adding the 6th tranny gear should allow us to cruise down the road at 70-75 mph and get the same fuel mileage as we get now at 55-60? I don't see any major problem as long as we don't try to tow in 6th and lug the engine too much. I would like to find out more about adding the solenoid!!
------------------
2001 Sierra 3500 SLE Ex.Cab 4WD Duramax/Allison
2002 Bigfoot 25C10.6 Camper... on its way???
VVVVVVVVVVVery interesting:
I just talked to a kid today that says his dads motorhome has a Allison 6sp with a cummins 245hp. (I think he said 245hp) He said is would climb hills great.
If they think the drive shaft spins to fast what about all the 4.11 and higher rear ends.
As far as mileage I hope ,when Gearvendors makes the back plate for my transfer case, I will get better mileage even with my ZF6 which I get only 17.5 or so around town. If not at least it should be less ware(sp?)on the engine
My 2cents. Roger
------------------
2002 2500HD/LS D/ZF6 Standard cab 4x4 summit white/tan interior
tow/camper/dual alt/lock dif/no carpet/fog/skid/Manick SS grillguard/Amsoil Airfilter/Amsoil dual bypass/preluber/pwrplay/
Check out the Allison web page, about halfway down the page it tells you the gears and ratios.
http://www.allisontransmission.com/product/series/1000series_specificationsheets.jsp
ChevysRus
12-14-2001, 23:53
Well it didn't make much sense to me either and that's why I threw it out here, but I am not a trans engineer so I am trying to understand it
What he was trying to tell me is that in 6th gear it's 1:25 meaning for every rpm of the engine something is turning 25 rpm in the trans and to the tailshaft and hence driveline. So at 2000 RPM engine speed x 25 rpm trans speed, something is turning 50,000 rpm. I don't believe the driveshaft could possibly turn that fast and still do 70 MPH.
It has taken me a while to grasp the concept that in overdrive the tailshaft is turning faster than the engine rpm. In order to maintain 70 MPH in overdrive the tailshaft and driveline has to turn faster than the engine rpm (if you lower engine rpm and maintain speed something has to be turning faster to maintain wheel speed right)?
First off I think he was talking about the bigger trucks that might have very high rear gears maybe over 5.0 and this would certainly raise the U-joint velocity, but that material is a hell of a lot bigger and stronger than our drivelines and offset somewhat by much bigger tires.
But I don't see the difference in running down the road now at 95 vs. running down the road in 6th at 70. I have not done the calculations, but would assume the driveline speed may be the same in both cases. So if it holds together at 95 mph in 5th, it should hold together in 6th at 70 mph.
Maybe this is why we can't get 4:11 gears with the Allison. Maybe these guys were jerking my chain and maybe I just didn't get the info right in my mind, but these guys have a multimillion dollar Allison dealership and are also the dealer for Detroit Diesel, so I am inclined to believe them if I heard it all right, but I still don't get it!
Maybe I will go back and have them add the solenoid and see what the hell happens.
IndigoDually
12-15-2001, 07:49
Just what we need, another gear for the trans to hunt for and downshift from when trying to use the cruise control. I like the idea of having another gear to slow down the RPM's but I think it would only be useful if it ciuld easily be shut off for towing unless you needed it.
ChevyRus,
When You talk to the dealer again ask them if there is a way to lockout 5th gear by adding a switch on the dash, this would satisfy many people including myself who use the 3rd gear option often and just locking out 5th would suffice. Thanks
------------------
'02 GMC 3500 Crew/longbed 4x4 (Wife's daily driver)
Indigo blue/Graphite leather/all the toys(you only go around once!)
G/N,Rhino,Western 8 1/2 UltraMount
My work truck:
'95 3500HD 15,000GVW
6.5 T/D 5 speed
chipped and exhaust mods
(with help of Kennedy)
10 1/2' Alum dumping flatbed
GN hitch
ChevysRus et al,
At the risk of launching into another debate, I'll comment on the u-joint/driveshift thing.
You can spin a driveshaft about as fast as you want, so long as it's designed and installed properly. Short driveshafts with low installed angles aren't usually a problem, but as length, speed and installed angle increase, you have do deal with what is called "driveline whip". That is where the driveshaft starts bowing in the middle due to the flexibility inherent in it's design; and that my friends, if it gets too bad (the whip), can result in shelling out the u-joints, and dropping the driveshaft. The correction is to make the driveshaft more stiff and/or reduce the installed angle. You make the driveshaft more stiff through some combination of tube diameter and tube wall thickness (am I gagging some of you guys yet with all this "Engineering BS" http://www.62-65-dieselpage.com/ubb/smile.gif)??
In Allison's Technical Data Books, there is a nomograph which shows the relationship between driveline length, speed, and tube size. For example, if you wanted to run a 55 inch driveshaft at 5000 RPM, you would have to have a tube diameter of 4 inches. I think the HDs have 5 inch driveshafts in them.
Bottom line, the CURRENT truck driveline may not be able to take the extra output RPM from a second overdrive, because it wasn't designed to handle it! That's not to say you couldn't do so, you just have to make certain all of the components which will see the additional speed are sized properly. http://www.62-65-dieselpage.com/ubb/smile.gif
huntindog
12-17-2001, 09:47
BigAl, you said -Bottom line, the CURRENT truck driveline may not be able to take the extra output RPM from a second overdrive, because it wasn't designed to handle it! That's not to say you couldn't do so, you just have to make certain all of the components which will see the additional speed are sized properly.
So you're saying that a sixth gear will cause the driveshaft to spin faster? Thats impossible unless the truck is going faster! Since we have speed limits and a governer to limit speed to 98 mph as well, I just don't see what you're trying to say. No one wants this extra gear to go faster, just more mpg.
------------------
Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
a64pilot
12-17-2001, 09:47
BigAl,
As drive shaft speeds are tied to rear wheel speeds wouldn't the rpm of the driveshafts be the same? Unless you change the rear end gear ratio.
------------------
2001 C3500 LT Charcoal Grey
CC/Longbed Putco boss boards,
virtual grill,mudflaps,sill protectors Rhino liner,
bug deflector. Looking into Boost/EGT gague
a64pilot
12-17-2001, 09:50
Sorry huntindog beat me to it eventhough the post times are the same
ChevysRus
12-17-2001, 11:44
Thanks Big Al, now I don't feel so dumb! Apparently there is some truth in all of this even if I don't clearly understand it.
I guess if we could look at that nomograph, maybe we would find out what RPM the driveshaft is turning now in 5th at 98mph amd maybe the real reason for the 98 mph limit is the engine rpm AND the driveshaft RPM are maxed out!
So if we had a 6th gear then the current driveline would max out at same RPM, BUT the MPH cutout would have to be reduced to maybe 75MPH in order for everything to hold together. I think maybe this is what Big Al is leading up to. We may be able to get a 6th gear, but we would have to accept a lower MPH cutout limiter with the current driveline components and that might be an unacceptable tradeoff depending where the calculations said the cutoff had to be.
I think I understand it all now.
Basically if we can get to 98 now and this is the max for driveline in 5th, then in 6th gear the driveline RPM may be maxed out at a lower speed and this lower speed whatever it is) may not be practical for the benefit of better MPG. If we beef up the driveline components (assuming this can be done economically) we can get back to 98 in 6th and have things hold together.
So everybody is correct in this, what we missed is that the 6th gear will increase driveline RPM and 6th gear may have to be held to a lower max speed due component failure at higher speeds.
OK hopefully this is it, everybody is right hurrah.
Now all we need to do is have someone make the calculations so this hypothesis will hold up ha ha ha
a64pilot
12-17-2001, 11:50
I hate to throw a wrench into things. The only way to change the collelation of driveshaft RPM to speed is to change the final drive ratio. I.E. tire and wheel size or final drive ratio.
Question, what is the airspeed velocity of an unladen swallow. http://www.62-65-dieselpage.com/ubb/confused.gif
------------------
2001 C3500 LT Charcoal Grey
CC/Longbed Putco boss boards,
virtual grill,mudflaps,sill protectors Rhino liner,
bug deflector. Looking into Boost/EGT gague
At 'X' vehicle speed, the driveshaft spins at 'Y' RPM regardless of the gear ratios in the transmission. What an additional overdrive ratio would allow is a faster truck, or the same speed truck at a lower engine RPM. In general, truck manufacturers used the 6-speed WT transmissions to provide for more performance on the lower end, vs. faster trucks, since you can choose where you use the extra gear based upon what axle ratio you use.
A governor on the engine would not limit the speed of the truck unless it was tied to vehicle speed. Most governors are tied to engine speed. Not knowing exactly how they work on the HDs, I couldn't say whether the governor would limit your truck's speed.
As far as speed limits go.......PU-LEASE! Since when did a speed limit actually limit most driver's speeds. Around here, if you're driving the speed limit your likely to be run down.
What I was saying was, unless the driveline in a truck is designed to handle the POSSIBILITY of greater driveline speeds, there is a risk to the components involved. Clearly, if all somebody uses an additional overdrive for is to run at the same vehicle speeds, but at lower engine RPM, there is ZERO additional risk to the driveline. However, barring some control (manual, mechanical or electronic) an additional overdrive would provide a faster top speed truck, and that means a driveshaft which could be spinning faster than it may have been designed for originally.
P.S. One of these "controls" I mentioned above could be a deeper axle ratio to maintain the original top geared speed of the truck! http://www.62-65-dieselpage.com/ubb/cool.gif
a64pilot,
Question, what is the airspeed velocity of an unladen swallow.
African or European? http://www.62-65-dieselpage.com/ubb/biggrin.gif http://www.62-65-dieselpage.com/ubb/biggrin.gif
------------------
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
<LI>Kennedy Diesel Headlight Harness with 4 Lamp Mode/Dual Alts with PowerMaster 200A
<LI>TransferFlow 56 gal tank w/Fast Fill fillneck/ROSTRA Obstacle Sensing System
<LI>Roll-N-Lock Retractable Bed Cover with Carbon Fiber Pattern/TracRac Sliding Rack System
<LI>Clifford AvantGaurd4 Alarm with Remote Start/SmartWindows4/Computer Interface for MS Windows/Turbo Timer Option
<LI>SPA DG-111 Digital Boost & EGT Gauge/PIAA Airdam/PIAA 80 Pro XT Driving & 959 Fog Lights
<LI>DTA Corp Running Boards & Mudflaps/Line-X/Invinca-Shield/Center Console Mods
<LI>Lucerix X-Mount Mirrors/Tekonsha Prodigy/Goodrich Velvet-Ride Shackles
<LI>Future Mods Include: Alcoas, Performance Module.... etc.
[/list]
An interesting and very informative topic, but really the main question should be, Is it posible, how difficult and how much will it cost to add the 6th speed.
IndigoDually
12-17-2001, 13:07
The limited speed of the truck would not change, just the limited rpm's at 6th gear lock-up. If you took off your stock tires and put on a set of o-rings like some of the low-riders run, the speedo would still read 98mph while your "actual" ground speed would be less because the truck would think that it is travelling farther per tire revolution than it really is. The same holds true with larger tires the truck is going faster than 98mph yet the truck still believes that it is only going 98 due to the value plugged into the computer for the stock tire size.
This is why it is important for speedo recalibration when you drastically change tire size due to shift points and other info that the computers need so the truck operates correctly and smoothly. The whole tire size issue relates to rpm's of the tires (REVOLUTIONS PER MILE) this number is more relative to the heavy truck market, when you look at tire brochures for large truck tires they usuaully list the number of revolutions the tire makes per mile because this is pertinant info for fuel economy and power when you deal with over the road trucks.
Well I think that the whole tire size over speed issue has been beaten to death on this post and I don't think that there is much more to say.
As for a 6th gear it just make our trucks too damn fuel efficient http://www.62-65-dieselpage.com/ubb/tongue.gif and it could cause the crude oil market to really go into a spin. Imagine if a full size pick-up could get 30+mpg the Arabs would be bent! http://www.62-65-dieselpage.com/ubb/mad.gif
------------------
'02 GMC 3500 Crew/longbed 4x4 (Wife's daily driver)
Indigo blue/Graphite leather/all the toys(you only go around once!)
G/N,Rhino,Western 8 1/2 UltraMount
My work truck:
'95 3500HD 15,000GVW
6.5 T/D 5 speed
chipped and exhaust mods
(with help of Kennedy)
10 1/2' Alum dumping flatbed
GN hitch
[This message has been edited by IndigoDually (edited 12-17-2001).]
[This message has been edited by IndigoDually (edited 12-17-2001).]
shft22,
An interesting and very informative topic, but really the main question should be, Is it posible, how difficult and how much will it cost to add the 6th speed.
Will the TCM need to be reprogrammed? If so, does this software exist for our GM trucks?
------------------
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
<LI>Kennedy Diesel Headlight Harness with 4 Lamp Mode/Dual Alts with PowerMaster 200A
<LI>TransferFlow 56 gal tank w/Fast Fill fillneck/ROSTRA Obstacle Sensing System
<LI>Roll-N-Lock Retractable Bed Cover with Carbon Fiber Pattern/TracRac Sliding Rack System
<LI>Clifford AvantGaurd4 Alarm with Remote Start/SmartWindows4/Computer Interface for MS Windows/Turbo Timer Option
<LI>SPA DG-111 Digital Boost & EGT Gauge/PIAA Airdam/PIAA 80 Pro XT Driving & 959 Fog Lights
<LI>DTA Corp Running Boards & Mudflaps/Line-X/Invinca-Shield/Center Console Mods
<LI>Lucerix X-Mount Mirrors/Tekonsha Prodigy/Goodrich Velvet-Ride Shackles
<LI>Future Mods Include: Alcoas, Performance Module.... etc.
[/list]
GreyPower3500
12-17-2001, 14:00
OK. If I understood all of that correctly (the top speed is a function of engine RPM and NOT a speedometer/vehicle speed input) then GM could assign a lower max RPM in SIXTH gear, then we wouldn't be able to exceed these driveline design limits, right ???
I'm OK with that --- there's hardly a highway near me where I could imagine running 98MPH, let alone 108...
All I'm after is a "less hectic" empty/lightly loaded engine RPM at 65-70MPH. The sixth gear route HAS to be easier than trying to cut and graft in 3.42:1 gearing into a 4WD, right ???
------------------
2001 K3500 Silverado LS 4x4 E/Cab DMAX/Allison Charcoal/Graphite, DEL Power-Tailgate, Draw-Tite Class IV receiver.
2001 Arctic Cat Pantera 1000cc - 172HP, no waiting...
huntindog
12-17-2001, 16:10
BigAl, ease up a little. I agree that speed limits are often treated as general guidelines. My point was that these are heavy duty trucks, not race trucks. If I want to go fast I have a muscle car to do it in. With the electronics in todays vehicles I would think the the governor is probably built into the computer and a simple "reflash" ought to take care of any excessive speed concerns.
------------------
Huntindog
2001 3500 4x4 CC D/A LT Husky liners, Husky mud flaps, Lucerix mirrors
Whoa guys!!!
You dont see the drivelines falling out of the 8.1's with the Allison and 4.10:1 gears. They are spinning those U-Joints much faster at their 98 mph than a DMax with its 3.73:1's. How about all the older trucks with 4.56 and 5.13's??? They went 98mph and some even faster. Somebody, somewhere will produce a kit in a year or two to transform the Allison into a 6 speed. They will probably make millions. Meanwhile GM will continue to brainwash its buyers into thinking that 5 speeds are more than enough, and 3.73's are the perfect gear.
The parts are all there on the shelves, let US order what WE want!!!
------------------
Thomas J. McCauley Jr.
Tommy's Lawn Service
Member # 5589
1990 K3500 SRW Ext.Cab Long Bed 454/400 3.73
1975 K20 Suburban 350/350 4.10's
Tows 16' Landscape Trailer
BOSS 8'2" V-Plow
7-11 MPG !!!
Duramax here I come!!
Company I used to work for had an '88 6.2 4 speed with 4.56 gears and the little dually tires! Broke lotsa everything BUT driveshafts!
Another gear would be nice, but Ive lived with 4.10's and single over this long...
------------------
John Kennedy
www.kennedydiesel.com (http://www.kennedydiesel.com)
John@kennedydiesel.com
2002 Chev. K2500HD Dmax/Allison Crew Cab Long Bed Pewter/Tan LT Due in any day now!
1996 GMC K2500HD 6.5TD Ex.Cab LWB 260+ Rw H.P.
1984 K30 SRW 6.2NA Headers and custom 2 into 1 exhaust FOR SALE
'01 FXDWG Black/Chrome Yellow (2 into 1 Thunderheader <naturally>) (100+ RwHP)
"If I had to explain, you wouldn't understand"
DmaxMaverick
12-18-2001, 05:23
I can't take it anymore! Gotta say something here......
The addition of a gear has no bearing on propeller shaft RPM what so ever. The only shaft/tranny relation with another gear would be the torque applied to the shaft and joints. 98 MPH is 98 MPH! The axle/propeller shaft/tranny output shaft will spin at the same RPM, no matter what you do in front of it, at the same speed. The VSSB pick-up is located at the output shaft of the tranny (or transfer case if 4X4). The truck's speed is limited to ~98 MPH by the VSSB, not the engine RPM. The engine RPM is governed at 3400 RPM. RPM is way less than that @ 98 MPH. Adding another gear will not allow higher speed, unless you defeat the speed governor, same without an extra gear. I don't know how the PCM/TCM would handle an extra gear, but its my guess that it would not care. It will calculate the ratio using engine RPM's and VSSB RPM's. It is just an algorithm. That is how it is able to detect tranny slip, which is doesn't even through a code until there is a 100 RPM difference. How much can the solenoid cost? I may be the first, but I'll try it. Put the solenoid on, put some juice to it and see what happens. Worst case would be DTC's that the dealer will clear anyway. They don't even have to know it was in there. Its my guess that if you install it, and the dealer drops the pan, they won't even notice. (trying to talk myself into it) If its that simple, as the Allison tech. that ChevysRus talked to.
My $2 worth. Take it or leave it........
------------------
2001 GMC 2500HD SLT 4X4 E/C SB loaded -D/A- Indigo Blue - Amsoiled bumper to bumper - Delivered November 2000
1985 K Blazer 6.2L N/A 500K+ original miles on Engine/Tranny (2 transfer cases, 1 pump, and a few rear ends)
Synthetic Oil!!
In order to add a 6th speed to the 1000 Series you need an add-on valvebody for the extra shift valve that does not exist at this time. You would also have to add a solenoid to control the shift valve. It (solenoid) is probably the same as one already on the current valvebody, so at least it's available. It's not as simple as dropping the pan and adding some "stuff" that's readily available. You would definitely have to reprogram the Control Module, cause it currently doesn't "know" anything about a 6th gear.
Now that I understand how the governor works on the HDs, I agree that you don't have to worry about u-joints or driveshafts. The observation that bigger rolling radius (revs per mile) tires cause the truck to run faster than the governor thinks it's running is absolutely accurate. In that case you would need to get the truck recalibrated to make certain the governor engages at TRUE 98 MPH, and to ensure your speedo is reading TRUE vehicle speed ("John Law" will help you with this if you want http://www.62-65-dieselpage.com/ubb/smile.gif)
My guess is you shouldn't look for 6th gear in a 1000 Series for 2 - 3 years. Some enterprising individual could try to come up with one on their own, but I sincerely doubt that will happen.
ChevysRus
12-18-2001, 11:53
OK then send this to the powers that be at GM. I would like to see a 6th gear in the DMAX. I have a 2001 and will probably be looking to trade in 2004. If the 6th gear is available in a 2003 I will trade then, 2004 meets my schedule perfectly. 2005 then I will wait and trade then.
It is GM's Patriotic Duty, to get this out on the market quick so we can be less dependent on Osama Bin Laden's oil squeezing "friend's" and raise the fuel mileage average for American HD trucks. I don't want to drive a fuel efficient Honda, I want to drive a more fuel efficient Chevy or GMC HD P/U!
Don't be fooled by today's low fuel prices, come 2002 Memorial Day weekend we will all be wondering how the fuel prices got back up to $1.80 a gallon so quick.
I want my 6th gear and I want it now! Log this under Customer Demand Trends or something equallly significant.
OK Merry Christmas all.
DmaxMaverick
12-19-2001, 00:55
Thank you BigAl. I didn't think it was THAT easy.
Drive a mile, walk the rest
11-19-2002, 10:50
Q: "frictional losses in both the engine and tranny are lower. But what percentage of the load on the motor is it?"
A: Frictional losses are estimated to be 6% for each gearbox with synthetic fluid.
Q: "And where does it crossover the loss in breathing efficiency?"
A: A duramax diesel will not crossover into a loss of breathing efficiency. Turbocharged, intercooled, fuel injected. The Duramax will pump in as much fuel and air as it needs.
Q: "why doesn't GM make the overdrive .5? Or .4?
A: The RPM drop from 1.0 to 0.4 would be too large. Excessive downshifting on small hills may become an issue.
Q: If taller is always more efficient, why not find the point where it will support 75mph unloaded with your right foot on the floor, and put the overdrive there? Or 95mph, since they have a limiter there anyway?
A: This is exactly how semi truck rearend ratios are specified. You choose your cruise speed and tire size, transmission final drive ratio. Then you calculate the rearend ratio so that your engine RPM is at the lowest operating RPM.
Q: Or ... could it be ... is it possible ... that *perhaps* it's possible to go too far?
A: Yes. Drivability issues would occur due to due to a lack of horsepower.
"Think it through, man. Present a cohesive argument. Don't just make claims you can't substantiate."
I have thought it through. There is a good arguement for a .6 ratio. I would like to "substantiate" the claim by adding this ratio to my truck and recording the MPG data. So....
HOW DO YOU ADD 6TH GEAR TO AN ALLISON!!??!?!????
solongpowerstroke
11-19-2002, 20:03
Just thought I would give my two cents worth on mileage increases with an extra (6th) gear. I beleive that this added gear could potentially DECREASE fuel milage. I have experienced this in dealing with rear differential ratios. My first truck was one that I built in high school. My dad and I built a 350 small block with a dyno proven 340 hp and 425 lb-ft of torque. When I first put the engine in the truck the fuel milage was a low 6-8mpg. At this time the rear end ratio was 3.07:1. After a few thousand miles I aquired a 3.73:1 rear end and slapped it in. To my surprise the fuel milage jumped to 10-12 mpg. Not bad considering that I was looking for more performance, not fuel milage. I think that there is a point where a load on an engine will decrease effciency because the throttle has to be depressed more to make the power to move the vehicle. There is a good chance that this point could be reached with the added gear.
Diggin' DEEP!
I wholeheartedly believe (don't start asking for facts!) that with STOCK tires 245's or 215's (duallys) the 6th gear (double OD) would without a doubt increase SOLO HIGHWAY MILAGE. Just about Every interstate highways' speed limit is 65mph+.
As for the hopped up 340/350 with 3.07's and then the move to 3.73's...Well that engine with its 340 hp had a peak hp at about 4500-5000 rpm and a peak torque at about 3500 rpm (roughly speaking). You were WELL below your ideal sweet spot on that engine. Also, you are talking rear axle ratio as a whole, and NOT an addition of another overdrive. You were constantly lugging that motor from 3mph to 55mph, while we are talking about just having the ability to engage a 6th gear when cruising the highways empty.
Big difference.
Diesel Freak
11-20-2002, 00:50
An additional overdrive will give you better mileage in an unloaded situation. I had a US Gear auxilary overdrive in my '94 Dodge Cummins, along with a 3.54 rear end. Talk about long legged! 85 mph was 2000 rpm on the nose. I did have increase the power of the motor (remember back then the Cummins was 175hp) I turned it up to 325rwhp and could easily get 22mpg on the highway, that's not babying it. I tried a couple of trips over the same stretch of interstate in overdrive and double overdrive, I would consistantly gain 1.5 - 2 mpg. Best I ever got with that truck was loafin' along at 1400 rpm in double overdrive, 24.7 mpg! That was in a 3/4ton 4x4 that weighed 7500lbs!
If I could get an aux. overdrive or a taller rearend for my Duramax, I'd do it in a heartbeat!
Paintdude
11-20-2002, 07:48
My 00 Z71 with 3.73 gears would cruise 65 at something like 1800 rpm..
a 3 speed transfer case would almost make more sence..Low-Tow-Mileage.This is the only way to meet everyones needs...IMO..
Maybe 3 sets of different sized wheels and tires.. :D
My '82 6.2L 2wd had overdrive and 2.76:1 gears. I honestly got 29 mpg a couple times on the highway. Until the original pump wore out I'd usually get 25-26 highway. My Dad's '84 6.2L 4x4 Blazer had 3.07 gears and also got 24-25 mpg highway. With all the added power we have there's no reason an added gear wouldn't help. 300 rpm lower is all you need.
Black Dog
11-20-2002, 09:01
I would suspect that there would be a problem with the clutches in the Allison slipping if you went to a steeper overdrive. They do not have a huge safety factor now, even with the .7:1 ratio, and stock engine torque output.
> A: A duramax diesel will not crossover into a
> loss of breathing efficiency. Turbocharged,
> intercooled, fuel injected. The Duramax will pump
> in as much fuel and air as it needs.
So you're telling that the Duramax breathes equally efficiently at all rpms? You get the exact same VE and cylinder fill at 700rpm as you get at 1400rpm as you get at 2100rpm?
If that's true, then why is the torque different at those three places? Not enough fuel? Then why don't they pump in enough fuel to give it a flat curve from idle to redline? Why does the motor have to get to 1800rpm before it reaches it's torque peak?
> Q: If taller is always more efficient, why not
> find the point where it will support 75mph
> unloaded with your right foot on the floor, and
> put the overdrive there? Or 95mph, since they
> have a limiter there anyway?
> A: This is exactly how semi truck rearend ratios
> are specified. You choose your cruise speed and
> tire size, transmission final drive ratio. Then
> you calculate the rearend ratio so that your
> engine RPM is at the lowest operating RPM.
So you're telling me semi trucks are always operated with the throttle on the floor? If not, why not? Hey, if taller is always more efficient, why not gear it so tall that it takes full throttle to maintain the desired cruising speed?
> Q: Or ... could it be ... is it possible ... that
> *perhaps* it's possible to go too far?
> A: Yes. Drivability issues would occur due to due
> to a lack of horsepower.
So the only reason they don't gear'em to the moon is driveability?
I agree that horsepower is key. It takes a certain amount of horsepower to support a given load at a given speed.
Now horsepower is torque times rpm, right? Can you explain to me WHY you believe maximum efficiency always comes when X amount of horsepower is made at the combination of lowest possible rpm (i.e. geared taller) and highest possible torque (i.e. more throttle), even if the motor's breathing is compromised by the rpm being too low? Please don't just tell me that it does, as you've done here, tell me WHY you believe that's the most efficient way to burn the fuel. If you've thought it through, that should be an easy question, right?
Drive a mile, walk the rest
11-20-2002, 14:20
ZFMAX,
Put this "horsepower = torque x rpm" thing out of your head. It is just distracting you. It takes a certain amount of torque so support a given load at a given speed. Go back and hit the books. Think about how engine torque overcomes vehicle resistance to maintain vehicle speed. Give yourself some time and it will all come together.
Then ask yourself "What would happen if an engine could generate the same or greater amount of torque with a lower engine RPM and the same throttle input?"
"It takes a certain amount of torque so support a given load at a given speed"
Hmm, okay, let's say we have two trucks going down the road, both making 200hp and both pulling the same load. You're saying the truck with the engine that's making the most torque will go fastest?
What if one of the truck's engines is making half as much torque, turning twice as many rpm, and is geared twice as deep? Won't it be going just as fast? And putting just as much torque to the rear wheels? And therefore able to pull the same load at the same speed?
Do you understand the relationship between torque, rpm, and gearing? Do you understand how gearing allows torque and rpm to be completely equivalent with respect to performance?
"What would happen if an engine could generate the same or greater amount of torque with a lower engine RPM and the same throttle input?"
Hmm, so the Duramax makes the same torque at 1000 rpm that it makes at 1800rpm? With the same throttle input? And that translates to the same amount of rear wheel torque, so long as they're geared for the same ground speed? So just gear it taller and presto, less rpm, same rear wheel torque, same throttle input?
What I want is another gear that let's me go 75 mph at 300 rpm less IF and only if I get the same or better mileage empty. Less rpm's mean less wear and tear on the engine and more mileage means less $$'s out of my pocket.
SoCalDieselNewbie
11-20-2002, 16:19
ZFMax wrote - "If that's true, then why is the torque different at those three places? Not enough fuel?"
Call Steve Cole or DuraMaximizer Joe... they'll tell you where the deficiencies in the fuel map are located and why.
ZFMax wrote - "Then why don't they pump in enough fuel to give it a flat curve from idle to redline? Why does the motor have to get to 1800rpm before it reaches it's torque peak?""
A couple of aftermarket guys essentially do that... Pacific Performance's towing program for the PCM, for example, is basically a flat torque curve that gives over 600 ft-lbs of torque from like 1500 rpm to redline.
ZFMax, if there was one thing that I truly dislike about my Duramax Allison truck, it is this... I get better mileage towing my boat at 65 MPH than I do @ 80 MPH in a truck that is UNLOADED!
This isn't a one time thing... I have gotten just over 17 mpg over the last 5,000 miles towing the boat and mid 15s going 80 unloaded. It is an every time thing and, quite honestly, I am going to do something about it.
I have already decided that the stock 215 tires are coming off the truck in about another 10,000 - 15,000 miles and I am putting 6 255/85R16 tires on.
For the way I drive, the change will be done in Jan 2003.
I hope that it will help.
SoCalDieselNewbie,
You may think your truck is unloaded at 80 mph because there is nothing in the bed or towed behind, but the wind resistance between 65 and 80 mph is loading your truck a huge amount. Good luck trying to solve that problem. Your best bet would be to drive your truck with a 50 mph tail wind at all times.
Don
Black Dog
11-21-2002, 06:54
As much as I hate to support the endless torque vs. horsepower debates:
Drive a mile wrote:
It takes a certain amount of torque to support a given load at a given speed.
This is just plain wrong. Substitute the word "horsepower" for the word "torque", and you have a factual statement.
*********** WARNING *****************
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********** TROLL ALERT **************
********** TROLL ALERT **************
DieselDennis
11-21-2002, 11:01
SoCal this is an issue with every truck. You're getting past peak effeciency when you run 80. If you have an EGT gauge I think that 600 degrees farenhiet pre turbo is around the effeincy neighborhood. Not like it as we may, that's just the way it is. Now with another gear to keep the truck at 80 and dropping the engine back into it's sweet spot would be a good thing IMHO.
Just look at some of the factories. They can pump out a million pieces a year and X amount of dollars per product. Now when they lean down and don't make so many products they don't make as much gross money, but they make more than the previous X amount of dollars per profit. So just slow it down.
SoCalDieselNewbie
11-21-2002, 13:03
Diesel Dennis,
I know that it is just a matter of slowing down.
Call it my impatience but, if conditions allow, I will never travel 10 mph under the Max Speed limit.
Interstate 10, in Arizona, and Interstate 15, in Utah & Idaho, are both posted at 75 MPH. I drive both of those highways alot. Heck usually, I am towing a boat or a toy trailer @ 75 mph.
Anyway, before you get on any of those two highways and go 65, give me a call... I'll hook you up with an anti-anxiety pill.
This truck's final drive ratio was engineered to run at 65 mph. With the true purpose of this truck in mind and the speeds that it will normally run at, GM did a great job in developing & engineering this drive line.
However, that doesn't mean that it shouldn't be customized to suit one's needs.
A manual overdrive of .61? I am ALL for it!
Drive a mile, walk the rest
11-21-2002, 20:15
SoCalDieselNewbie,
I will be changing tires to 285's in about one month. I have the same driving habits and mileage complaints. I will let you know how much my mileage increase.
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