HORSEPOWER & TORQUE
Horsepower is defined as 33,000 foot pounds of work per minute.
When dealing with automotive engines. You need to measure units of force from rotating objects such as crankshafts. So, you use terms which define a "twisting" force, such as foot pounds of torque. A foot pound of torque is the "twisting" force necessary to support a one pound weight on a weightless horizontal bar, one foot from the fulcrum.
Now you need to visualize that one pound weight, one foot from the fulcrum on its weightless bar. If you rotate that weight for one full revolution against one pound of resistance, you have moved it a total of 6.2832 feet (Pi X a two foot circle). You have also done 6.2832 foot pounds of work.
As stated above, 33,000 foot pounds of work per minute is equivalent to one horsepower. That was definition was formulated by a man by the name of Watt.
If you divide the 6.2832 foot pounds of work you've done per revolution of that weight into 33,000 foot pounds, you come up with one foot pound of torque at 5252 rpm's is equal to 33,000 foot pounds per minute of work. That is the equivalent of one horsepower. If you only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute). SOOOO, the following formula applies for calculating horsepower from a torque measurement:
Horse Power = Torque X RPM / 5252
Torque is the only thing you feel in a car. Horsepower is just sort of a generic comparison. 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. If you put it in the formula, the horsepower would be "double" at 4000 rpm; therefore, horsepower isn't particularly meaningful from a driver's perspective. The two numbers only get closer at 5252 rpm, where horsepower and torque always come out the same.