Old PH post (written by fritz_269):
HP = (Torque * RPM) / 5252
Torque is measured in Foot*Pounds (ft*lbs) or Newton*Meters (N*M) - (the above formula works for ft*lbs)
Picking up one pound from the ground to one foot off the floor is one ft*lb of WORK. Torque is a measure of WORK, expressed for a twisting motion (like an axle or a tire).
Horsepower is a measure of POWER.
POWER = WORK/TIME.
If it takes you a day to pick up that 1lb weight, you don't have much POWER. If you do it in a millisecond, you've got a lot of POWER. To move a car fast, you have to have a lot of POWER.
RPM (Revolutions per Minute) is what gives us the time relation in the formula, and we see that HP is always a linear multiple of Torque. If anyone tells you different, they don't know what they are talking about. HP and Torque are always strictly related through RPM.
Big V8 engines have a lot of torque at low RPMs, but have a lower RPM redline. They have to get their HP from a big Torque number. Honda NA 4cyl engines have a low Torque, but a very high redline - they can get their HP from a high RPM number. You see, there are two ways to get HP -> Torquer vs. Twister.
