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Hey guys, whats the difference between horsepower and torque? I know the technical, torque gets things moving and horsepower is the power of the engine, but in the real world. For example, a mustang GT is about a half a second quicker to 60 than a 350Z, yet they both have the same hp, rwd, and the Z weighs about 100 pounds less. It seems like they should be almost identical. The only thing I can think, besides gearing, is the torque (320 for the GT and 260 for the Z). I know from a roll or from different speeds, they may be much closer. But if thats the case, why were the muscle cars of the 60's with very high torque and fairly high hp, not as fast as say a ferrari with high hp and fairly low torque? Of course without taking into consideration the aerodynamics, suspension and gearing superiority of the ferrari.
 

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http://vettenet.org/torquehp.html

The Case For Torque
Now, what does all this mean in carland?

First of all, from a driver's perspective, torque, to use the vernacular, RULES :). 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, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching pushback 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? Fine. Can we go on, now? :)

The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?

Because (to quote a friend), "It is 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 carland for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), 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 drivewheels 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 drivewheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, 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 HP.

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.


more to read in the linky.
 

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Discussion Starter #4
Ok, I think I got it. If you have higher hp (or a higher revs), you can continue, or extend, the torque much farther than a car with less hp.
 

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dont limit yourself to hp revs and gearing...
deasil trucks dont make much hp and dont rev fast but ive seen quite a few deasil dodge trucks run very very low 1/4 times
 

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it is really a case of examining the area under the curve.

Hot rod had a great articel a while back "boost shoot out"

Long and short a 5.0 with a centrifugal blower made 611 HP and the same 5.0 wit ha turbo only made 595. So by street logic the 611 HP motor is better than a 595 right? Wrong, because the Trubo motor made 650ish TQ at 4500 rpm while the CF made lessaround 550 TQ a 5700 rpms. While the SC motor might pull harder for that very last bit of redline (the last 3-400 rpm) in the midrange the turbo motor would run away.

So peak numbers cannot always help you out either. The mustang and Z scenario is a great example. The mustang makes it torque very low in the RPM band and carries it, it has much better area under the curve meaning that it makse more AVERAGE torque. The 350 on the other hand does not have as much torue in the lower rpms!

The MS6 is another good example. if you put our 2.3L Turbo motor at 274 HP against a 230's 287 HP in an identical car, our 274 would smoke it most likely because of the super flat torque curve, the 350 makes good power, and decent torque, but over a comparitively limited rev range.

Hope that helps some!

dont limit yourself to hp revs and gearing...
deasil trucks dont make much hp and dont rev fast but ive seen quite a few deasil dodge trucks run very very low 1/4 times
[/b]
This is true, and 300 HP from a desil (if geared properly) should perform as well as 300 HP from a mustang all else being equal, but there is never going to be a scenario when a 300 HP desil is as light as a 300 HP mustang motor!

HP is basically torque re stated, but realise that you can get

Honda S2000
237 @ 7800 rpm
162 @ 6800
8,000 RPM redline

OR
Mazda CX7
244 HP @ 5,000 rpms
258 Lbft @ 2400 rpm
6700 rpm redline


Near identical peak HP but VASTYL different torqu numbers, torque RPM's and redlines....
If you hooked these motors up to a custom ride with identical weights and proper gearing they would for all intensive purposes respons very simmilarly, th only difference being that the mazda motor has a much borader torque curve and solid midrange.
 

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I don't know much about the torque to horsepower deal myself, but I have heard constantly that horsepower sells cars and torque wins races.
 

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http://vettenet.org/torquehp.html

The Case For Torque
Now, what does all this mean in carland?

First of all, from a driver's perspective, torque, to use the vernacular, RULES :). 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, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching pushback 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? Fine. Can we go on, now? :)

The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?

Because (to quote a friend), "It is 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 carland for a moment, and describe a waterwheel I got to watch awhile ago. This was a pretty massive wheel (built a couple of hundred years ago), 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 drivewheels 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 drivewheels is around one mph for the average car, and, in order to go faster, we'd need to gear it up. To get to 60 mph would require gearing the wheel up enough so that it would be effectively making a little over 43 foot pounds of torque at the output, 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 HP.

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.
more to read in the linky.
[/b]

Very nice Q and A....
 

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Hey guys, whats the difference between horsepower and torque? I know the technical, torque gets things moving and horsepower is the power of the engine, but in the real world. For example, a mustang GT is about a half a second quicker to 60 than a 350Z, yet they both have the same hp, rwd, and the Z weighs about 100 pounds less. It seems like they should be almost identical. The only thing I can think, besides gearing, is the torque (320 for the GT and 260 for the Z). I know from a roll or from different speeds, they may be much closer. But if thats the case, why were the muscle cars of the 60's with very high torque and fairly high hp, not as fast as say a ferrari with high hp and fairly low torque? Of course without taking into consideration the aerodynamics, suspension and gearing superiority of the ferrari.
[/b]

Power bands are different in those two cars as well.
 
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