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NWBowTie, There were two good articles on the DMAX/8.1. I have the first one here on my desk. It is the Oct.2000 issue. Both trucks were towing 10,400 lbs. The times are listed below. I have the second article. I just have to find it. Later! Lone Eagle
Demax 8.1
0 to 60 solo 9.5 9.0
0 to 60 towing 24.4 30.3
40 to 60 towing 13.0 16.4
When buying a new Farm tractor, which spends most of its time pulling at close to full load. We look at and buy Horsepower. One tractor size produces 375 Horsepower at 2000 RPM's and 410 HP at 1800 RPM's, while the other tractor produces 325 Horsepower, and 350 at 1800 RPM's. It isn't the torque but the horsepower that we are paying six figures for. The reason that the horsepower increases from 2000 to 1800 RPM's is that the peak torque is lower than 2000 and increases at a faster rate than the RPMs decrease. Providing more horsepower to do the work. And yes these engines are all rated at over 1000 ft lbs of torque. MORE LOW END TORQUE = MORE LOW END HORSEPOWER!
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
That's the way I recall it, the 8.1 will out accelerate the DMax, towing is another story. As we all know the most difficult scenario for a gasser is when it tows up a hill and the RPMs drop from the HP sweet zone. The DMax's torque maintains hill climbing speeds while using more a fuel efficient torque sweet zone at lower RPMs.
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'01 Silverado 2500HD Dmax/Allison EC 4x4 SB, Westin Bars, Fumoto Valve
"Assuming it's geared properly, the truck with the most horsepower is going to get the trailer to the top of the hill first, not the truck with the most torque. This isn't my opinion, it's a fact of physics."
Boy, now I'm really confused. Let's see, the Duramax outpulled the 8.1 with a load of 10,500 lbs. So, the 8.1 must not be geared properly???
Anyway, it looks like you need that torque to increase that rpm to get that horsepower going, but once you get moving, the horsepower takes over provided there's enough of it to keep the rpm up, and if there isn't, the torque has to increase the rpm again through a gear change, so that the horsepower can take over again. (Sounds like handoff from a fullback to a halfback...) Anyway, pulling my boat up a steep ramp slightly above idle does it for me. I like that torque...
I need a beer...
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BBugg
No, more horsepower = better acceleration as well. The vehicle with the most average horsepower over it's operating range will accelerate the best.
I can't account for one set of anectdotal results.
I'm just repeating myself. I'm going to stop now. This is pure physics. I haven't given one single opinion.
Hunter98 has it exactly right.
ZFMax,
I've been following this post and I applaud your patience. You've done a great job taking a complicated physics problem (work) and explaining it in layman's terms. I sure wish I had you for a study partner when I took my dynamics course. At this point, I think you might want to defer to Kennedy's quote in his signature. http://www.62-65-dieselpage.com/ubb/wink.gif
ZFMax
According to my dusty old college physic textbook your right on. None of my professors ever presented the subject as clear and concise as you did--congrats.
As for as the 8.1 not being geared right: It might not be a case of right or wrong gearing but that the available transmissions favor the power curve of the Duramax over that of the 8.1.
Wow, thanks guys. It's good to know someone was following all that drivel!
So, was the original question answered?
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'93 GMC SLE 6.5TD Banks Power Pack D/A Sle XC/LB 4WD TPW 01-01-02 GOA NRA EAA AOPA AMA VFW Good Sam Cessna 180
I hope that you all understand now! Rear end gearing is wonderful at allowing you a tall enough gear to run more efficiently, or to have a low enough rear end (4.10.4.56) to get a load started in first gear, or to have enough power at highway speed to be able to tow the load. I.E. A truck with a 4.10 rear end traveling at 2200 RPM's will have more horsepower available than the truck with 3.73 at 2000 rpms. With the Duramax's power curve that is virtually flat at 500-520 ft-lbs, that 10% more RPM's equates to 10% more horsepower available at max throttle at that RPM to move the load.
My truck contraversially enough runs about 4 mph faster at the quarter mile with my 33" tires, than with the 30.5" tires that were factory. This is attributed to the fact that the truck is now geared better to take advantage of the power band. It shifted to 5th before at too low of a speed to take advanage of all the power.
If you gave the 8100 a 10 or 13 speed, it would work great as a grain truck. But who wants to spend all day cruising around at 4000 to 5000 RPM's.
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
I was always tought in simplest terms HP is the measure of the rate at which work is done. If nothing moves then no HP has been applied. Torque is a twisting force that can be applied and have nothing move.
Both numbers are very important for pulling loads up a hill. HP is how fast it can pull it up the hill and torque is how much it can pull it up a hill. If you have three engines with 300 HP and one has 520 TQ, one has 600TQ and one has 700TQ. Loaded the one with the most torque will pull the hill fastest. Now if you have three engines with 520 TQ one has 300 HP, one has 240 HP and one has 200HP. The 300 hp engine will pull it fastest.
Not to long ago Ford, Dodge and Chevy Diesels made around 180 HP and around 450 TQ. My big block gasser made 235HP and just shy of 400TQ. With 10,000 pounds of trailer I could climb 6% grades on the east coast faster than the diesels could. Now with the New much higher HP diesels and some more torque they can out climb that truck.
I know my duramax will out climb my last gasser. Better yet it will get better mpg. But it has more HP and more Torque. The older diesels with more torque but less hp could not.
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2001 Chevy LT C3500 Crew Cab Dually, Duramax, Allison,pulling 12500 pound Holiday Rambler Alumilite.
If you have three engines with 300 HP and one has 520 TQ, one has 600TQ and one has 700TQ. Loaded the one with the most torque will pull the hill fastest.
I'm curious as to why you believe this?
Doesn't 300hp, after gear reduction to any given rear wheel speed, ALWAYS translate into the same amount of torque at the wheel? Regardless of the torque at the engine?
Let's just see ...
with 300hp & 520ft/lbs of torque, how much rpm are we turning? rpm = (hp * 5252) / torque:
(300hp * 5252) / 520ftlbs = 3030rpm
How much gear reduction do we need to turn 3030rpm into 772rpm at the rear wheels (70mph)? gear reduction = input rpm / output rpm
3030rpm / 772rpm = 3.925:1 gear reduction needed
If we apply 3.925:1 gear reduction to 520ft/lbs of torque, how much torque will we get at the rear wheels? output torque = input torque * gear reduction
520ftlbs * 3.925 = 2041ft/lbs of torque at the rear wheels
Now let's repeat those steps for 300hp & 600ft/lbs of torque:
(300hp * 5252) / 600ftlbs = 2626rpm
2626rpm / 772rpm = 3.401:1 gear reduction needed
600ftlbs * 3.401 = 2041ft/lbs of torque at the rear wheels
Hmm, came out the same. Maybe 300hp & 700ft/lbs of torque:
(300hp * 5252) / 700ftlbs = 2251rpm
2251rpm / 772rpm = 2.916:1 gear reduction needed
700ftlbs * 2.916 = 2041ft/lbs of torque at the rear wheels
Hmm. All 3 combinations put 2041ft/lbs of torque to the rear axle at 70mph.
The first thing they teach you in physics class is that force = mass * acceleration. As long as the force and the mass are the same, the acceleration should be the same, right? So why do you think one of these will out-accelerate the others?
I think whoever taught you had it wrong.
Let go of this notion that the combination of torque and hp is what matters for towing performance. Torque is a component of horsepower. The ONLY thing implied by a high combination of the two that the motor is turning less rpm, because horsepower is torque * rpm. You're not saying it can accelerate or climb a hill faster. Only the combination of torque (force) and rpm (rate of application) describes that property (assuming you're geared correctly). And the combination of torque and rpm is called Horsepower.
[This message has been edited by ZFMax (edited 01-15-2002).]
ZFMax, I applaud you for your tenaciousness and your concise and accurate explanations. But not matter how hard you try, some of us will never get it. At some point in time you must use Slpashot44's suggestion. "I think you might want to defer to Kennedy's quote in his signature." Jim
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2001 SILVERADO /2500HD EXT CAB /LWB/ DURAMAX / ALLISON / 4X4 / LT / HUSKY MUD FLAPS /
FIRESTONE AIR BAGS/
ZFMax,
Now, that was a fantastic explanation and see that easy math doesn't apply when trying to figure what's going to do the job better.
Now, I'm going to have to crunch some numbers to figure out how much weight my buddy was pulling on about a 7% grade with his F**d PSD and walked right by 7.4L 4:10 gasser and a V10 stuper duty. The gassers were both holding to metal about 35-40 mph and the PSD was able to pass at about 50 mph. It might be that both the gassers were over 60K on miles and the PSD was new. Thanks again for spending the time in your reply, Wow! http://www.62-65-dieselpage.com/ubb/cool.gif
ZFMax,
http://www.plauder-smilies.com/nosmile/claps.gif http://www.plauder-smilies.com/nosmile/claps.gif
Now would you mind explaining http://www.plauder-smilies.com/nosmile/atom.gif cold fusion http://www.plauder-smilies.com/nosmile/atom.gif , my 5th grade son had to write a 1 page report on it last week because everyone in the class was talking in the hall. No kidding - Catholic school. http://www.62-65-dieselpage.com/ubb/wink.gif
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mdrag
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'01 3500 "BIG DOOLEY" DMAX/ALLISON PICTURES<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, 4" Exhaust, Performance Module.... etc.[/list]
This is for all of us who are "wrong". I spoke with James Watt last night and he never heard of a D/A... "Torque Rules"
Check out this website out if you haven't had enough:
http://www.boston-bmwcca.org/bimmer/...nd-torque.html
Here's a sample:
The Case For Torque
First of all, torque rules, from a driver's perspective. Any given car, in any given gear, will accelerate at a rate that exactly matches its torque curve, allowing for increased air and rolling resistance as speeds climb. Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear. Yet, if you start plugging figures into that formula, you can see that the horsepower would double at 4000 rpm, with the same level of acceleration. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the horsepower and torque numbers only get friendly at 5252 rpm, where they always come out the same.
In contrast to a torque curve (and the matching push back into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver feels.
You don't believe all this?
Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? OK. Now that we're all on the same wavelength (and I hope you didn't get a ticket or anything), we can go on.
The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?
Because (to quote a friend), "It's better to make torque at high rpm than at low rpm, because you can take advantage of gearing".
For an extreme example of this, I'll leave car land for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a long time ago down in Sturbridge, MA), rotating lazily on a shaft which was connected to the works inside a flour mill. Working some things out from what the people in the mill said, I was able to determine that the wheel typically generated about 2600(!) foot pounds of torque. I had clocked its speed, and determined that it was rotating at about 12 rpm. If we hooked that wheel to, say, the drive wheels of a car, that car would go from zero to twelve rpm in a flash, and the waterwheel would hardly notice.
On the other hand, twelve rpm of the drive wheels is around one mile per hour for the average car, and, in order to go faster, we'd need to gear it up. If you remember your junior high school physics and the topic of simple machines, you'll remember that to gear something up or down gives you linear increases in speed with linear decreases in force, or vice versa. To get to 60 miles per hour would require gearing the output from the wheel up by 60 times, enough so that it would be effectively making a little over 43 foot pounds of torque at the output (one sixtieth of the wheel's direct torque), which is not only a relatively small amount, it's less than what the average car would need in order to actually get to 60.
Applying the conversion formula gives us the facts on this. Twelve times twenty six hundred, over five thousand two hundred fifty two gives us: 6 horsepower.
OOPS. Now we see the rest of the story. While it's clearly true that the water wheel can exert a bunch of force, its power (ability to do work over time) is severely limited.
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BBugg
Guys, you're very kind, and I appreciate your comments. And I know, I should not keep doing this. But at the same time, should we let misinformation be posted here and go unchallenged?
Like that drivel in the first part of bbugg's post ...
Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it.
This is true, BUT, it fails to consider the fact that you're going two different speeds at the torque & hp peaks.
For a given ground speed, however, you'll accelerate harder if you've geared the vehicle to be at it's horsepower peak instead of at it's torque peak. That's a fact. I'll refrain from giving examples, but if anyone followed my other examples it'll be obvious. Why do you think the transmission downshifts when we floor it?
Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300
foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear.
Same deception is at work in that statement. If you're making the same torque at twice the rpm, that means you can apply twice as much gear reduction and still be going the same speed. And then you'll have TWICE as much torque at the rear axle and you'll acclerate TWICE as hard!
Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker?
That's a poorly designed experiment that proves nothing. Do it this way instead. Take it to it's torque peak in TOP gear. Punch it. Now, slow back down to the speed where you punched it, and downshift to a gear that puts the engine at it's horsepower peak instead. Punch it. It'll be noticeably stronger. That's why we downshift and wind up our motors when we climb hills. Horsepower wins every time, because for a given ground speed, it describes how much torque can be sent to the rear wheels.
Still don't believe me? Get two trucks with ZF's going side by side, each at 2000rpm. Have one guy romp on it, and have the other guy downshift and THEN romp on it. Who do you think will accelerate the hardest?
Bottom line, if you're going to compare acceleration at the horsepower peak versus the torque peak, you have to equalize the speeds where the comparison is made, otherwise it's an invalid comparison.
Okay, I'm done. Really. People can post all the misinformation they want, I won't react. If you believe me, need any swampland in Florida?
[This message has been edited by ZFMax (edited 01-15-2002).]
An experiment for all Duramax owners that are 2002 or have had the Cruise control update. Set the cruise at 70 MPH which is about 2000 RPMs, just over the peak torque, and floor it. Ok, see how she responds at that RPM without downshifting. Click the CC off now and try it again and FEEL the POWER!
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
ZFMax,
I did not say out accelerate. I said climb the hill at a faster rate of speed.
Every physics class I have had stated HP is the rate at which work can been done, that means how fast. Torque is the twisting force available. You can apply torque an not move anything. If nothing moves you have not used any HP.
As for the statement about the 454(7.4L) and 4.10 gears. Not the right set up, only rated for 10,000 pounds. The 454 needs the 4.56 gear. Then it will run in the hills with most stock diesels, prior to the 2001's. I know my 96 Crew Cab dooly with the 454 and 4.56 gears pulling 12,000 pounds would run a way from my friends 97 quad cab dodge cummins 4.10 and an 10,500 pound RV on the saluda grade. Now with my crew cab dooly duramax and 3.73 gears I can climb the saluda grade 4 mph faster than I could with the 96, that means 58mph. Not bad, but I want to pull 12,000 over it at 70mph.
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2001 Chevy LT C3500 Crew Cab Dually, Duramax, Allison,pulling 12500 pound Holiday Rambler Alumilite.
Okay Dave, I'm confused.
Loaded the one with the most torque will pull the hill fastest.
Every physics class I have had stated HP is the rate at which work can been done, that means how fast
These two statements contradict each other. Which is it? (hint: your understanding of hp is incomplete)
Anyway, I showed that all 3 of the 300hp motors you described (520, 600, and 700ft/lbs of torque) put the EXACT same torque to the rear wheels at 70mph. The torque at the engine is irrelevant.
If they all have the exact same combination of torque and rpm at the rear wheels, why do you think they'll climb a hill at different speeds?
Isn't it the forces acting on the rear wheels that matters? Why does the specific combination of torque/rpm at the engine matter at all for towing performance?
Didn't we use gearing to convert the engine's combination of torque/rpm into the combination we need at the rear wheels? And didn't 300hp always come out the same, no matter what it's makeup at the motor?
I did not say out accelerate. I said climb the hill at a faster rate of speed.
Doesn't torque available at the rear wheels determine how fast something can go? As well as it's acceleration?
If I have a moving object, and a force of 2000lbs resisting it, won't it accelerate if I apply more than 2000lbs of force and decelerate if I apply less than 2000lbs of force? And if I apply more than 2000lbs, won't it accelerate until the force resisting it matches the force I'm applying? Thereby ending up at a higher speed?
So I repeat my question. At 70mph, all 3 of the 300hp motors (520, 600, 700 ft/lbs) put the SAME force to the rear wheels. Why do you think they can climb at different speeds?
[This message has been edited by ZFMax (edited 01-16-2002).]