BHP stands for brake horsepower and is the measure of an engine's power without the loss of power from adding the drivetrain, alternator, water pump or other auxiliary equipment. Wheel horsepower is the term used to describe the power after adding all necessary equipment and auxiliary equipment.
Brake horsepower was originally used to test the power output of steam engines. James Watt coined the term horsepower as a way to market his new steam engine. Watt used this term to compare the pulling power of a horse to a steam engine. John Desaguliers later determined that a horse could produce about 27,500 foot-pounds per minute. Foot-pounds is an American measurement used for work or to describe a vehicle's torque. On average, a physically fit human produces about 1.2 horsepower for a short time and 0.1 horsepower indefinitely. The word "brake" in "brake horsepower" represented the device that was used to hold the engine at specific revolutions per minute, or RPM.
Determining the brake horsepower of an engine is very important when designing a vehicle. The engine must produce enough power to drive all of the components required to move the vehicle. Understanding the power output of the engine also allows the engine maker to produce a more efficient engine and meet required safety standards.