///M-Spec
Staff Emeritus
- 4,928
skicrushWithout a doubt. There are tons of things I never took into consideration. In a nutshell, force times distance is work. Work over time is power. There are 2 ways to get more power from an engine. More force, or more distance (rpms). But we're WAY past acceleration. F=MA, or Acceleration = force over mass=Meter/sec^2 (a lot messier than 0-60 in x sec.). You have to get torque at the rear wheels, to take gearing into effect and get the real amount of torque reaching the road, but acceleration is all about weight and torque.
Ah good. No replies in a few days, which means I can safely continue hijacking this thread.
I agree with everything in that paragraph except for the last sentance. Torque is force over distance, but it is not the same thing as work. They use the same units, but are not interchangable. 1 lb-ft of torque is 1 pound of force acting on a point 1 foot away through an imaginary (massless) lever. It is not the same thing as moving a 1 lb object 1 foot in some direction. That's why you can't interchange torque with force the formula you used earlier.
I do agree torque at the drive wheels is what's important, BUT the way you phrase the statement can be misleading.
Think about this: there are two engines. Let's assume for sake of simplicity they have the exact same dimensions and weight. They have the following torque curves.
Engine 1
200 @ 2000
300 @ 3500 < peak torque
240 @ 5000
230 @ 5500 < peak hp
200 @ 5700 < redline
Engine 2
110 @ 2000
140 @ 5000
160 @ 6500 < peak torque
158 @ 8000 < peak hp
150 @ 8500 < redline
Engine 1 makes TWICE the amount of torque at it's torque peak of 3500 RPM. But at the red line, it makes 241 hp.
Engine 2 makes it's seemingly flacid peak torque of 160 at 6500 RPM. But it revs all the way to 8000 at which it is making the same 241 hp that Engine 1 makes.
If you put these engines into identical RWD cars, and change the final drive to suit the power curve of each motor, I submit both cars will accelerate pretty much at the same rate.
The bottom line is torque at the crankshaft is misleading, because you don't take RPMs into account. Torque at the wheels is useful, but why not just calculate for horsepower at the wheels? When some get their car dynoed, they are interested in WHP and the shape of their curve, not WT.
M