Brake horsepower (BHP) is the amount of power generated by a motor without taking into consideration any of the various auxiliary components that may slow down the actual speed of the motor. Sometimes referred to as pure horsepower, brake horsepower is measured within the engine's output shaft. Depending on the configuration of the engine, the point on the output shaft that is the focus of the measurement is the engine dynamometer.
The reference to this type of horsepower measurement as brake horsepower has its origins in the braking systems that were used on some of the first automobiles in the early 20th century. In many instances, cars were equipped with a hand brake that would slow the forward projection of the vehicle. This same hand brake was also used in the manufacturing process to gauge the amount of torque created within the motor, making sure the output was within acceptable limits.
In the actual calculation of brake horsepower, it is necessary to consider the total load of the electric motor. This means disregarding any drain on the power that is due to the water pump, generator, or the gearbox that work in conjunction with the motor of the vehicle. The amount of power loss that occurs due to the action of various belts and pulleys is also added back into the base figure, making it possible to determine the true amount of pure horsepower being generated by the motor.
Understanding the brake horsepower of a motor is key to ensuring the output is strong enough to drive both the motor and any auxiliary components. By measuring brake horsepower, it is possible to determine how much power must be produced to allow the motor to function at peak efficiency with the core functions. At the same time, calculating a proper brake horsepower that will supply an adequate amount of power to all complimentary devices found under the hood will ensure that many of the one-time extras available on vehicles that are now considered standard features will work properly. As a third benefit, measuring brake horsepower also helps manufacturers to produce engines that meet all current safety regulations for engine types within a given classification.