10 Notable Differences Between HP and BHP You Should Know : Current School News

10 Notable Differences Between HP and BHP

Filed in Education by on April 21, 2021



Difference between HP and BHP: When dealing with Motors, one of the questions that come to mind is the difference between Horsepower (HP) and Brake Horsepower (BHP).

Difference Between HP and BHP

HP and BHP are units of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. The difference between these units is what this article seeks to explain.


Horsepower is measured by a rolling dynamometer at the wheels of the car- this is the most useful, as it is what you feel when you drive the vehicle, so this is often the one called “Horsepower”. It is a term to describe the power of an engine to do work and is derived by multiplying the force generated by the distance traveled in a given time.

It is BHP deducted for loss in the transmission and differential and wheels, brake drag, any mechanical load placed on the BHP value by the car’s systems. Horsepower is invented by James Watt

Brake Horsepower

Brake Horsepower refers to how horsepower is measured: a brake like the one on the wheel of a car is attached to the rotating output shaft of an engine that converts the mechanical energy into heat.

A scale attached to the brake measures the torque applied and a tachometer measures the shaft speed, and those two numbers can be used to compute the power delivered to the brake. If you clamp the brake down tighter, more torque is applied to the brake, and more power is converted to heat.

A device that measures mechanical power is a dynamometer (or dyno), so this is called a “brake dyno”. One problem with this simple way to measure horsepower is that the brake will quickly overheat.

horse power

An alternative is to attach a water pump to the engine and measure the flow rate into an elevated tank. This is known as a “water brake”.

The only thing that is special about “brake horsepower” is that it is measured at constant RPM. We can see how an engine performs for minutes on end at max RPM and full-throttle.

Notable Distinctions Between HP and BHP

1. HP is the output horsepower rating of an engine, while BHP is the input brake horsepower of an engine.

2. BHP is the measurement of an engine’s power without any power losses, while HP is BHP less the power losses.

3. HP is measured by hooking up the engine to a dynamometer. However, BHP is measured in a controlled environment without anything attached to the engine.

4. HP is a general term to mention the power output.

5. BHP is more ‘pure’ than HP.

In summary, HP is measured with all the accouterments attached to the engine, to determine its maximum rate and speed. Meanwhile, BHP is more of a theoretical calculation, which is made under lab-controlled conditions, and without having anything attached to the engine.

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