Torque and Power - EngineKnowHow

Simplified, torque is what puts you in the back of your seat and power is what keeps you there.

Technically, torque is a measure of an engine’s ability to do work and power is the rate at which the engine is capable of doing work (Energy).  Torque can also be considered as the twisting force from the crankshaft and is measured in Newton.Meters (Nm).

Torque is measured by a dynometer and is used to calculate Power via:

 

 

 

or:

 

 

 

Note that power is only a function of engine speed and torque.

 

Examples

The plots below provide the torque and powercurves for several 2L, 4 cylinder engines with varying ignition types and modes of aspiration.  Note:

  • The turbo and supercharged engines have higher torque due to the increased mass of air in the cylinder at combustion.
  • The flat maximum torque of the boosted, spark ignition engines is managed for engine safety due to increasing engine knock, higher cylinder pressures and temperatures.
  • The boosted engines having a lower compression ratio then the naturally aspirated engine due to increased knock limitations.
  • The supercharged engine has the highest initial torque.
  • The compression ignition (diesel) engine has the highest compression ratio (required to ignite the fuel).