Originally Posted by Jspeed
This power vs. torque debate can go on and on... because neither side is wrong.
If you could only find out one thing about an engine, the HP is definitely more important than torque. It's just physics, and HP includes torque. However, to really get to know an engine, it's the area under the torque curve that matters. (it's still some form of average power, since width of the area is rpm and height is torque)
Keeping in the segueing theme here...
I not so sure if the area under the torque vs rpm curve has any particular meaning. Sure more is better but that is almost the same as saying more power at all rpms is better (or more torque...).
What does have a meaning is the integral in time
of torque x rpm (well in SI units torque x ω, but the same thing if you have consistent units). This gives the total work done by the engine or equivalently how much change in kinetic energy has been given to the vehicle. From that you get exactly how fast it is going. The key thing is you need to plot torque vs. time, not torque vs. rpm. There is a key shortcut here as well though because power is just torque x ω (again basically torque x rpm but in SI units). Thus you can time integrate power instead of messing with torque and rpm! Power is fundamental!
Knowing power is absolutely more fundamental as it does not matter what the gear/final drive ratios are. But of course if you know the full torque curve vs. rpm then you can get the full power curve. You just CAN NOT use crank torque alone in many equations to determine speed or acceleration where you can use power alone! That's the power of power.