Brake Torque and Power

Engine torque is normally measured with a dynamometer .The engine is clamped on a test bed and the shaft is connected to the dynamometer rotor .

The torque exerted by the engine is T    :          T = F b

The power P delivered by the engine and
absorbed by the dynamometer is the
product of torque and angular speed :

              P = 2 (pi) N T

Where N is the Crankshaft rotational speed .

In SI units :
                                                      -3
P (kw) = 2 (pi) N (rev/s) T ( N.m ) * 10

In U.S units :

                        N ( rev/min) T ( ibf.ft)
       P (hp) = --------------------------------------------
                            5252

Note that torque is measure of an engine's ability to do work ; Power is the rate at which work done .

The value of engine power measured as described above is called brake power Pb .This power is the usable power delivered by the engine to the load - in this case ,a brake .