differences between hp and bhp

Hi friend,
Generally engine power output is expressed in horsepower (hp).Both hp and bhp are same only. HP is a general term to mention the power output. Brake horse power(bhp) is a specific term to express the power output at the engine shaft.
The power delivered by the combustion products on the piston of an IC engine is called indicated horse power (ihp). This whole ihp is not available at the engine shaft and fraction of power is lost due to frictional forces and some of the power is used for pumping the gases, opening the valves etc and the remaining power is available at the shaft and this power is called brake horse power(bhp). This can be expressed as an equation

bhp = ihp - fhp

where, fhp means frictional horse power which includes all the frictional losses and pumping power spent.

The units of all the terms are in horsepower only.

Horse power 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.

To measure horse power, we use a brake to apply a load to the engine so we can measure the work done to overcome the load, hence the term brake horse power

When we apply the brake, to hold the engine at constant speed at full throttle, we can measurethe reaction of the brake as a force, expresed as torque as it is a force trying to turn the brake.

We multiply the torque force by engine speed and divide by a constant about 5000 and something from memory if the torque is in foot pounds and the speed is in rpm, to convert that power to horse power or brake horse power.

Regards
pat

At the moment, I've got the vehicle speed, and by calculating the rolling resistance, Aerodynamic drag,running resistance, the power is calculated. By using this value, I converted it to horse power. What do I needed, to convert it from horse power to brake horse power?

Nothing

The brake in brake horse power is simply that some people include the method of measurement in the result in this case.

It is like calling a small measurement vernier millimetres instead of millimetres, because you used a vernier to make the measurement.

I guess it came into effect to distinguish it from calculated rather than measured horse power.

About a centry ago, they used to have a thing called rated horse power and they used a formula based I think on bore size and compression ratio, or soimething equally as ridiculouse

Regards
pat

Nothing is required to convert horse power to brake horse power. You can say the power you calculated is simply horsepower or brake horse power. Both are same only.

KMP

I agree, in theory.

On the other hand MSCW may be trying to work back to a shaft horsepower at the engine, in which case a transmission efficiency is needed from engine to wheel contact patch.

Modelling said efficiency is less than straightforward, but if you've got a manual gearbox in top gear then figure on 98% for the gearbox and perhaps 97% for the rest, roughly.

Cheers

Greg Locock

B.S.
Brake horsepower is something car manufactures dream up to make there engines sound better.
Horsepower is a continuous output and is, (torque in ft lbs * RPM)/5252.
Brake horsepower is derived differently, and I don’t know how. If you take a car motor and use the peek torque & rpm quoted to calculate the horsepower it will be different than the brake HP.

If you take a car motor and use the peek torque & rpm quoted to calculate the horsepower it will be different than the brake HP.

But if you use torque @ peak power speed, you get the right number! (peak power happens at a higher engine speed than peak torque)

I was told years ago that horse power wqas measured at the crankshaft and brake horsepower was measured at the wheels...taking into consideration driveline losses.

hogwash?

brake horsepower was correctly described by patprimmer. The term "brake" distinguishes it from "indicated," "gross," "net," or other power quantities that are commonly used in discussion. Brake horsepower is the amount of power at the output shaft.

Check out the following site for some useful definitions:

And to clarify:

Any of the last three mentioned on the linked page could be referred to as "brake" horsepowers because they are measured in a mechnical fashion, whether it be a water-brake or a chassis dyno. As many have said - brake refers to the fact that it was measured as opposed to calculated or inferred from other data.

As I understand it:
Before about 1972(ish), OEMS quoted gross brake horsepower. They now quote net brake horsepower. They usually drop the "brake", it's already a mouthful!

HP at the shaft is different than the HP at the wheels,
the best way to determin HP is to put your car on a
rear wheel dyno, and do the test.

Detroit in the HP race used some deciving methods
to show how their car or engine had the most HP.
RWHP is the most accurate way to determin real
work that is being performed.