When a piston is pushed down a cylinder during the power stroke it applies force to a connecting rod linking the piston and a crankshaft bearing, causing the crankshaft to rotate. The rotational force applied to the crankshaft is called torque.
The metric unit for the measurement of torque is Newton meters, the imperial measurement is pounds feet.
If a force of 100 Newtons is applied to the end of a 1 meter long lever attached to a shaft perpendicular to its axis, the resulting torque applied to the shaft will be 100 Newtons per meter, or 100 Newton meters.
Similarly, a force of 100 pounds applied to the end of a 1 foot long lever would result in torque applied to the shaft of 100 pounds per foot or 100 pounds feet.
When an engine applies torque to a rotating shaft and that torque is allowed to act through a rotational distance, mechanical work is being done. Power is the term used to describe how much work is done in a period of time.
The measurement of engine power is calculated from the amount of torque applied to the crankshaft and the speed at which it is turning. When expressing engine power it is necessary to express not only the power value, but to include the engine speed, in revolutions per minute, at which it occurs.
Power is measured in Kilowatts or Horsepower. A kilowatt is equivalent to one thousand Newtons per meter per second. One Horsepower is equal to thirty three thousand pounds per foot per minute.
