The most important parameter measuring engine performance is specific fuel consumption [c]. This is a measure of fuel used per unit thrust (or per unit power) produced by the engine.
c = lb of fuel consumed per hour / lb of thrust produced
= lb of fuel consumed per hour / hp produced by engine (hp : horse power)
= kg of fuel consumed per hour / kN thrust produced
= kg of fuel consumed per hour / kW of power
Other definitions involved in discussing engine performance are
bhp : brake horsepower: Horsepower at the output shaft of an engine, turbine, or motor is termed brake horsepower or shaft horsepower, depending on what kind of instrument is used to measure it.
It is the measure of an engine's horsepower before the loss in power caused by the gearbox and drive train.
shp : shaft horsepower :Shaft horsepower (shp) is the power delivered to the propeller shafts (transmission losses)
These lead to the inclusion of propulsive efficiency.