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Fuzzy math, remember that term from the presidential election?
ZFMax...so what.
"Anyway, I showed that all 3 of the 300hp motors you described (520, 600, and 700ft/lbs of torque) put the EXACT same torque to the rear wheels at 70mph. The torque at the engine is irrelevant"
Yes you did but you changed the gear reduction ratio in all of your examples.
My truck does not have an adjustable rearend. Does yours?, is there a switch I have not found that lets you switch gear reduction in the rear end?
So use your numbers again keeping the same gear reduction but different torque input. My calculator says that the output tourqe will change.
But then again....so what. I will never buy an arguement that says you if keep HP the same and increase torque and you will have no increase in real world driving/towing performance.
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2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
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Power = work/time
That's why The Diesel Page compares the Ford/Dodge/GM trucks on a 6% grade with the same trailer. "Work" is pulling a 10K trailer a measured mile up a 6% grade. "Time" is the elapsed time it took to get from point A to point B (mile marker to mile marker).
Results - an off-the-shelf Duramax "truck" always produces the most "power".
MP
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Yes you did but you changed the gear reduction ratio in all of your examples.
Well, if you have 3 different engine rpms, and you want all 3 trucks to run the same speed, you pretty much have to change the gear reduction, no?
My truck does not have an adjustable rearend. Does yours?, is there a switch I have not found that lets you switch gear
reduction in the rear end?
No, not that I know of. But they provide a different way to change gear reduction, this thing called a "transmission". There's this big lever coming out of the floor with 6 forward speeds and a reverse. It's described in the owner's manual. There's a couple different types you can get.
So use your numbers again keeping the same gear reduction but different torque input. My calculator says that the output tourqe will change.
What does your calculator say about the output rpm?
300hp = 520ft/lbs of torque @ 3030rpm
520ft/lbs * 3.925 gear reduction = 2041ft/lbs torque at the rear wheels
3030rpm / 3.925 gear reduction = 772rpm rear wheel speed (70mph)
300hp = 600ft/lbs of torque @ 2626rpm
600ft/lbs * 3.925 gear reduction = 2355ft/lbs torque at the rear wheels
2626rpm / 3.925 gear reduction = 669rpm rear wheel speed (60.66mph)
300hp = 700ft/lbs of torque @ 2251rpm
700ft/lbs * 3.925 gear reduction = 2748ft/lbs torque at the rear wheels
2251rpm / 3.925 gear reduction = 574rpm rear wheel speed (52mph)
Sure enough, if we raise torque at the motor, and keep the hp and gearing the same, we raise torque at the rear wheels. No argument.
But now you're going slower. Hmm.
You could've accomplished the same thing by just downshifting. For example, if I have the 520ft-lb/3030rpm engine, and I just downshifted to a gear that gives me 5.284 of total gear reduction instead of 3.925:
300hp = 520ft/lbs of torque @ 3030rpm
520ft/lbs * 5.284 gear reduction = 2748ft/lbs torque at the rear wheels
3030rpm / 5.284 gear reduction = 574rpm rear wheel speed (52mph)
What's the difference between this and the 700ft-lbs/2251rpm combination geared at 3.925:1?
Tell me again why a high torque/low rpm combination of 300hp will outperform a low torque/high rpm combination of 300hp?
Bottom line, there's no free lunch here. Torque and rpm are equally important. Your argument ignores rpm.
I will never buy an arguement that says you if keep HP the same and increase torque and you will have no increase in real world driving/towing performance.
Funny thing about the laws of physics, whether or not we believe them doesn't change them a bit.
I'm a big fan of diesel pickups. I got my first one 10 years ago. I will never own another gas powered pickup. The combination of towing power and fuel efficiency and longevity is worth the extra money to me. But, I don't kid myself into thinking that my 300hp is somehow stronger than someone else's 300hp just because mine is made of higher torque at a lower rpm. That'd be silly.
[This message has been edited by ZFMax (edited 01-16-2002).]
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ZFMax'
I took physics in college, too. That's why I am a mechanical engineer. We all know that it's the throttle that makes it go up the hill! http://www.62-65-dieselpage.com/ubb/rolleyes.gif You have a lot of patience! but you are correct. Jet engines have a lot of torgue, too, but it just makes the airplane roll http://www.62-65-dieselpage.com/ubb/smile.gif Force = Mass X Acceleration and Horsepower is Force over Time--torgue doesn't even enter the equation. It is used on a dyno to calculate horsepower by spinning wheels on a load cell. In an airplane we measure force directly by pulling on the load cell. Well, that's my $.02 worth.
Joe
[This message has been edited by Allison Jettester (edited 01-16-2002).]
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Thanks, Joe. I also are an in gan ear (if that wasn't obvious by my obsession with such mundane matters)
The real problem here is that too many people have it stuck in their heads that torque is some separate property that you can have in addition to horsepower, rather than looking at it as a component of horsepower. But old notions die hard. Sigh.
[This message has been edited by ZFMax (edited 01-16-2002).]
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ZFMax.
"Sure enough, if we raise torque at the motor, and keep the hp and gearing the same, we raise torque at the rear wheels. No argument.
But now you're going slower. Hmm."
Kinda sounds like the reason low end torque is useful in a diesel engine. You gain pulling power at a lower RPM. Fuel efficiency is a benefit. With more power at a lower RPM (and speed in your simplistic augument) I can do one other thing, Speed up. Hmm. By doing that I still have more power at the wheels.
And given a one sided simple viewpoint the laws of phyics apply. Apply multiple inputs and you have the real world.
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2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
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Kinda sounds like the reason low end torque is useful in a diesel engine. You gain pulling power at a lower RPM. Fuel efficiency is a benefit.
Yep! But that's a separate metric than pulling a trailer up a hill.
With more power at a lower RPM (and speed in your simplistic augument) I can do one other thing, Speed up.
Do you mean by just applying more throttle and raising rpm?
Keep in mind that the basis of our debate is that all these different motor configurations make 300hp. They're just making it with different combinations of torque & rpm.
If you raise rpm, and horsepower stays at 300hp, then torque has to go down.
Hmm. By doing that I still have more power at the wheels.
I thought we agreed that all of these configurations have 300hp?
Go back and check every single pair of torque & rpm figures in those examples, whether they're at the engine or at the wheels. They're all 300hp. hp = (torque * rpm) / 5252
Are you saying you have some way to take 300hp at the engine and have more than 300hp at the rear wheels? And the way to do this is to make the 300hp with higher torque and lower rpm?
Show me.
And given a one sided simple viewpoint the laws of phyics apply. Apply multiple inputs and you have the real world.
I hate to break this to you, but the laws of physics describe the real world. That's what the whole field is about, understanding the real world and the rules that govern it. If you think I missed an input, please let me know which one it is.
I really think you've got it stuck in your head that torque is something you can have in addition to horsepower. I don't know why you're so married to that concept. It's wrong, and as long as you cling to it, you'll continue trying to rationalize that somehow the physics isn't real world.
Torque is a component of horsepower. The other component is rpm. A high torque version of X horsepower means low rpm, nothing more. A low torque version of X horsepower means high rpm, nothing more. Once you gear them for the same rpm, you'll have the same torque. That's not an opinion, and it's not leaving out an input, and it's as real world as anything gets.
[This message has been edited by ZFMax (edited 01-16-2002).]
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ZFMax: How I wish you had been my physics teacher back in high school. Instead of struggling for an MBA, I might have accomplished a PHD in mechanical engineering.
Your analysis and the examples you utilized, have clarified this question for me.
Now I know my Duramax diesel is a better choice to power my truck than 300 horses. And no poop to clean up either!
Thank you for sharing your knowledge.
01 Chev K3500 D/A LT Crew LBx
Diesel page member #40
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ZFMAX,
Lets hope you are self employed, because you are spending way too much time at work teaching physics.
Everyone else,
The funny thing is that we are still stuck with the main question does the DMAX make the power claimed.
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2001 Silverado
3500CrewCab, 4x4, Duramax/Allison
Towing a 40' Enclosed Exiss 2 car race trailer.
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ZFMax,
One more try and I'll let it end, for the good of all mankind.
Trust me here I KNOW torque is a component of horsepower. That is why you can't say:
"All of this really points out why it's truly horsepower that matters, not engine torque." It is a component after all right?
It's important to remember the dyno measures torque and rpm and then from these calculates horsepower. On the dyno it takes more water flow to the water brake to increase the load on the engine being tested. As the test engine's torque rises more water flow is needed. As the test engine's torque drops less water flow is needed. The dyno's water brake does not respond to horsepower. Major adjustments to water flow are needed as an engine crosses its torque peak but none are needed as it crosses its horsepower peak. In other words the water flow to the brake during a dyno test follows the engines torque curve and not its horsepower curve. Torque is what twists the tire, prop, or pump. Horsepower helps us understand an amount or quantity of torque. (Torque + time)
At or below 5252 rpm any engine's torque will always be higher than its horsepower, and above 5252 rpm any engine's horsepower will always be higher than its torque.
Why because they are a component of each other.
One more point (I promise RWHP)!!
Horsepower can be converted into other units as well. For example, 1 horsepower is equivalent to 746 watts or 2,545 BTU (British thermal units) per hour. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts. If you took that 746 watts and ran it through an electric heater, it would produce 2,545 BTU in an hour (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F). One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, the horse would burn 641 Calories in one hour doing its work if it were 100-percent efficient. So if horsepower is the be all end all, I will burn 192300 calories driving my truck for one hour. I'm hungry and tired.
Mark
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2002 Chevy 4x4 CC D/A
Jayco 325BHS
http://www.PictureTrail.com/maburns
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Sigh. To teach something, the other person has to actually want to understand. This is a waste of time.
Oh well, it's nice to know all this 'splaining was helpful to some. Thanks. I'm done.
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I have read about all I can get my hands on concerning this subject and I have not read one document outside this forum that does not state that torque determines acceleration. I even spoke with a couple buddies that race funny cars and they put torque over horsepower. These guys will be at the Winter Nationals and that ain't no drivel. Actually, contrary to one fella, I see no drivel here.
Lexus puts out an engine that has variable valve timing eliminating the usual compromise between low-end torque and high-rpm horsepower Why not just more horsepower??
When I selected a cam for my Harley, I picked a high torque cam, cause I like to be quick off the line. Should I get my money back from Crane??
Because people do not agree, does not mean they do not want to understand, and be careful, because it goes both ways.
In any case, there has been a lot of thought and work put into these two pages and I've enjoyed reading everything.
I will have to admit that I demonstrated this torque/horsepower thing to my girlfriend and she preferred horsepower... so there, I'm wrong!!
Anyway, I've pasted one last article just to bore everyone. If you think it says horsepower is more important, you might want to stop here...
"The terms horsepower and torque can be confusing at times. One of the top authoritative magazines on engines, Hot Rod Magazine, took twenty pages to explain torque vs. HP. Here's a paraphrase of what they said.
Simply defined, horsepower is the rate of doing work over a given amount of time. According to experts from SAE, one horsepower (1 HP) equals 550 ft-lb. per second or 33,000 ft-lb. per minute. Another familiar formula is the one which states RPM x Torque / 5252 = horsepower
Torque is the measurement of the strength of the rotational movement and determines how fast a car, boat, or airplane accelerates up to a required speed.
An example here should be helpful:
Think of a V-8 car engine that puts out approximately 300 HP or more at 6,000 rpm compared to a large diesel semi-truck that puts out 300 HP at 2,200 rpm. They are both 300 HP engines; however, they are very different and offer different performance capabilities. The V-8 car engine puts out 300 HP and produces 263 ft-lb. torque at its top working speed of 6,000 rpm. The diesel truck engine puts out 300 HP but puts out 716 ft-lb. torque at its top working speed of 2,200 rpm.
If you put the V-8 car engine into a diesel truck (even though it is also 300 HP) it can not even move the truck. This is because the low speed strength (TORQUE) of the V-8 is not sufficient to even get started. The diesel engine has much higher torque but is very large in size and weight, i.e. 700 - 900 cubic inches and 2500 lb. in weight. And obviously, you could not put a diesel engine in a car because it is too big and heavy."
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BBugg
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Mr. ZFMax, could you please step off the soap box. My 21 years in school AND my job teaching, (I think) show a desire to learn.
The components of horsepower are force, distance and time. Distance and time are self-explanatory but force, specifically a twisting force, is what torque is all about. Torque is stated as foot-pounds and represents how much twisting force is at work
As you may have noticed, this measurement of torque does not include time. One-hundred foot-pounds of torque is always 100 foot-pounds torque, whether it is applied for five seconds or five years. So, if you want a quick answer to the difference between horsepower and torque, just keep in mind that horsepower involves the amount of work done in a given time, while torque is simply a measurement of force and is thus a component of horsepower.
So now we have a technical understanding of how torque interacts with horsepower, but let's move beyond that to some real-world examples. For instance, we all know that a car moves from a dead stop in 1st or low gear, yet as the car's speed increases, the gears must be moved up through 2nd, 3rd and 4th to maintain acceleration. This is because at low speeds the transmission's gears work to transmit maximum torque from the engine to the wheels. (ahhhh the torque of a diesel) You want this because it takes more force, or torque, to move a vehicle that is at rest than it does to move a vehicle in motion (by the way ZFMax, that
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Of course torque determines acceleration.
Torque at the rear wheels!
And torque at the rear wheels will be at it's peak, for a given ground speed, when the motor is at it's horsepower peak. I proved that. Several times!
If you put the V-8 car engine into a diesel truck (even though it is also 300 HP) it can not even move the truck. This is because the low speed strength (TORQUE) of the V-8 is not sufficient to even get started.
You still don't understand the concept of gear reduction, do you? Because the V8 is making it's 300hp at 6000rpm instead of 2200rpm, you can apply almost three times as much gear reduction to it for a given speed. This multiplies it's lower torque into the same torque. Look at the examples above.
If you still insist that you can accelerate hardest from a given speed at your torque peak, or if you insist that you can pull a trailer up a hill best at your torque peak, go right ahead. Just stay in the right lane, okay? Because I'm going to downshift, put my engine at it's horsepower peak, and go around you. Every time.
Y'all have closed your minds. As Marks comments about gearing clearly demonstrate, you don't understand the role of gearing. But I've explained it every way I can think of.
[This message has been edited by ZFMax (edited 01-17-2002).]
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"And torque at the rear wheels will be at it's peak, for a given ground speed, when the motor is at it's horsepower peak. I proved that. Several times!"
How and when did you prove that?
I have seen about numerous post on dyno results that have (Rear Wheel)Max HP of around 250 @ 2900 RPM. Max Torque is around 475 ft lbs @ 2600 rpm. Torque drops off after that.
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How and when did you prove that?
Read the examples. It's all there.
I have seen about numerous post on dyno results that have (Rear Wheel)Max HP of around 250 @ 2900 RPM. Max Torque is around 475 ft lbs @ 2600 rpm.
As I explained before, those dyno charts are showing engine torque as measured at the rear wheels, not rear wheel torque. There's a big difference. Engine torque does not reflect the multiplication you get with the gear reduction offered by the transmission and rear axle. If you only had 475 ft/lbs at your rear wheels, the truck couldn't get out of it's own way.
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I want to be done TOO!, Torque shows how much HP is produced at a given RPM. More Torque means more HP, and that is why Torque is important. If an engine produced 650 Ft. Lbs at 1400 RPMs, and 450 Ft. Lbs at 2000 RPMs, compared to an engine like the Duramax that produces roughly 520 at both points, give me the 520. With the 650 at 1400 RPMS the important HP number is 173, at the 2000 and 450 ft lbs it would be 171. Hmmm, now with this engine the RPM's increased, but the HP didn't, now with the Duramax, at 1400 RPM's, would produce 139 HP, and at 2000 RPM's would produce 198 HP, hmmm, the HP increased this time. I would rather have the ability to have increasing and the Higher HP, than the higher torque. I will bet any one of you that whether your 650 ft lb engine was at 1400 or 2000 RPM's, I would pass you in my Duramax at 2000 RPM's!, Now you say that your 650 can be made at 2000 RPM's, well you now produce 247.5 HP, which is why you could now pass me.
Higher Torque is a function of when the engine makes its HP, a diesel is a High Torque engine, and inherently produces its HORSEPOWER at lower RPM's than a gas engine.
DO I WANT MORE TORQUE, A RESOUNDING YES, BUT I WANT MORE TORQUE BECAUSE IT WOULD GIVE ME MORE LOW END HORSEPOWER, without sacrificing the high end!
If you don't get it by now, go back to my moms class in fourth grade, maybee she can explain it better! http://www.62-65-dieselpage.com/ubb/wink.gif
Hunter
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2 :D :D 2 GMC SLE Ext Cab SB 4x4 Pewter/Graphite
Duramax/Allison/Eaton
Kelly AWR 255x85R16,
GM bedrail caps and folding cupholder, Husky Floormats
Westin CPS Nerf Bars
http://www.picturetrail.com/hunter98
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Let's put this one to bed with PullinPower's test in the Industry News Forum!!
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ZF is talking about the rear dif here. 3.73:1 makes for a significant torque increase.
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Mike (dmax) DP Member #2429
2001 2500HD GMC Duramax/Allison Summit White CC/SB Loaded
Amsoil Air Filter, Straight Piped PIC
PS2K Propane, 22 Gal. LP Tank PIC
Allison Deep Pan, Transynd Syn ATF PIC
SPA DG-111 Boost/EGT, Nordskog Digital Fuel Level PIC
VentShades, Husky Mudflaps, 255/85-R16 Dunlop Radial Rover RV's
Kennedy Headlight Booster Kit TRUCK PICTURES CLICK HERE
1994 K1500 Blazer 350 Loaded, Flowmaster duals
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Mark, work out how much torque you'll get to the rear wheels at the torque peak you provided, 475ft/lbs @ 2600rpm (235hp). Do it at any speed you want, it doesn't matter if it's 1mph or 1000mph.
Now, using the exact same ground speed, work out how much torque you'll have at the rear wheels at the horsepower peak instead, 250hp @ 2900rpm (452ft/lbs).
If you don't know how to do this, I'll show you. Or look in my previous example of the 3 300hp engines.
Tell me which one puts more torque to the rear axle for a given speed, running at the horsepower peak or running at the torque peak?
Think of any other example of different horsepowers and torques you want to give, I don't care. Pick 400hp & 100ft/lbs of torque compared to 300hp and 1000ft/lbs of torque. Which is capable of putting the most torque to the rear wheels at ANY given speed? Mark? Bbugg?
Torque is made in an engine through the combination of combustion pressure and stroke (stroke is mechanical advantage on the crank).
But what you're missing is that there's another way to make torque, too. We can gear something down. The more rpm we start with, the more we can gear it down, and the more torque we can put at the rear wheels. So rpm is *really* important. In fact, it's just as important as the torque we start with. This is what you guys aren't getting.
Hmm, if *only* we had a number that combines both torque and rpm into one number http://www.62-65-dieselpage.com/ubb/wink.gif
That would be ideal, because it would truly tell us how much torque we could put to the rear wheels for any given speed.
Doggone it, where could we get such a number? I guess we could multiply torque and rpm, that would give us a combination of both. What do you think? You think that would do a better job of telling us how much torque we can produce after gear reduction than just engine torque or rpm alone?
Let's do it! One more thing, though, to make the number more meaningful, can we divide it by 5252 as well? That'll scale it down to where it approximates how much torque a horse can generate at it's normal speed. And then we can name it after the horse. Any ideas for a name? Hmm, something that represents horse, and power, let me see ...
[This message has been edited by ZFMax (edited 01-17-2002).]
