Torque is turning or twisting force. The power developed in an engine’s cylinders is converted into a turning force by the crankshaft, which delivers this torque to the drive train where it is transmitted to the wheels. Torque is measured in pounds-feet (lb-ft), although it is often casually expressed as “foot-pounds,†which is actually a measure of work. In the metric system, torque is given in Newton-meters (Nm) or kilogram-meters (kg-m).Horsepower is the rate at which torque is produced. One horsepower was designated many years ago as the amount of work required to lift 550 pounds one foot in one second.The torque and horsepower an engine can deliver vary with engine speed. Note that maximum torque is developed at low to moderate RPM, while brake horsepower (the power available at the end of the crankshaft) continues to rise into the high RPM range. At higher RPM, the torque and horsepower curves begin to drop, due to difficulties in the engine’s breathing at the higher speeds.
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