Torque

Engine output is measured in two ways. The first is a direct measurement of engine output: Torque. Torque is defined as the amount of mass that can be lifted a certain distance from the centre of rotation (measured in LB-FT in America and N-M in the rest of the world). Torque is what accelerates a car. It is what pushes you back into your seat when accelerating.

The expression of twisting force around an axis is called torque, which is measured in units of force times distance from the axis of rotation. If you have a 1-foot-long wrench and you exert a force of 10 pounds on the end of it then you apply a torque of 10 pound-feet (10 lb-ft). If the wrench were 2 feet long, the same force would apply a torque of 20 lb-ft. When an engine is said to make “200 lb-ft of torque”, it means that 200 pounds of force on a 1-foot lever is needed to stop its motion.

The equation for torque is given below:

The U.S. measurement system, the unit of measure for torque is the pound-foot (lb-ft), while for work it is the foot-pound (ft-lb). Remember, work and torque aren’t the same. The Movement must occur for work to be done, but that doesn’t necessarily hold true for torque: Exerting ten lb-ft of torque on a bolt that’s already been tightened to 50 lb-ft won’t produce any movement.

If torque does produce movement, as is the case with your engine unless it’s locked up any “distance” travelled as the crank rotates is equal to the circumference of a circle, not a straight line. So one lb-ft of torque produced during one revolution is about equal to 6.28 ft-lb of work or mechanical energy.