7 replies to this topic

[coopersmate]

Hi
I have been wondering for a while now. What is the difference between Horse power and break horse power?
Can anyone explain this in layman's terms?

Thanks
Lloyd

[kez_19]

Horse power

The horsepower was originally defined to compare the output of steam engines with the power of draft horses. The unit was widely adopted to measure the output of piston engines, turbines, electric motors, and other machinery. The definition of the unit varied between geographical regions. Most countries now use the SI unit watt for measurement of power. The use of horsepower in the EU is banned since the implementation of the EU Directive 80/181/EEC on January 1st, 2010.

Brake horsepower

Brake horsepower (bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc. Brake refers to a device which was used to load an engine and hold it at a desired RPM. During testing, the output torque and rotational speed were measured to determine the brake horsepower. Horsepower was originally measured and calculated by use of the indicator (a James Watt invention of the late 18th century), and later by means of a De Prony brake connected to the engine's output shaft. More recently, an engine dynamometer is used instead of a De Prony brake. The output delivered to the driving wheels is less than that obtainable at the engine's crankshaft.

hope that helps

michael

[Trail of Dead]

I have been wondering this myself.....if I said "Brake Horsepower" in the states I would be getting some awfully strange looks from people. We just simply say "Horsepower". BUT based on what I read in Kez's post Brake Horsepower is the same thing as RWHP/FWHP (Rear Wheel Horse Power/Front Wheel Horse Power). Example, my Mustang saw 320 horse at the flywheel but at the rear wheels I was around 290 horse. So I guess this is what The British would call "Brake Horsepower"....the 290 part of it. Am I right?

[Guess-Works.com]

Simple terms...

Horse Power is achieved by a mathematical calculation, same as watts is the product of Current and Voltage in electrical terms.

Brake Horse Power is calculated from an actual torque figure, ie the amount of force which is required to arrest the acceleration of a mechanical device, in this case, a driven wheel. It could equally be a crank figure if the engine is run up on an engine dyno.

[coopersmate]

So to sum up (and please correct me if I have got this wrong)

Horse power

An old unit of measure not really used any more. If someone out of the steam engine community is referring to horse power they probably mean break horse power.

Break horse power

A measure of power of an engine either at the crank or the wheels. Calculated by looking at the torque, rotational speed of the rollers and the load (or break) on the rollers.

Is this right?
Does anyone one know the formula or have a link to it?

Thanks

LLoyd

[kez_19]

here you go

michael

[Trail of Dead]

"If someone out of the steam engine community is referring to horse power they probably mean break horse power." Well, I wouldn't consider myself a part of the Steam engine community but I certainly don't say "BHP" or Brake Horsepower. Honestly, the way I see it there is a "definition" of the differences between the two terms but in practice I think we both are referring to the same thing. Know what I mean? The only real world difference (between two men standing around a car holding beers in their hands) is the term "BHP" just isn't widely used in the states....you would get some blank stares if you said "How many Brake Horsepower does it have?". I know that isn't the point to this topic, I am just making an example. It just seems in use they seem to mean the same thing between men that could care less about mathematical calculations.

If you take your car to the dyno and it gives you lets say....85BHP then it is the same as 85HP. To people that care about nit picky data type things then they may want to argue about it. It's like "ToMAYtoe" or "ToMAtoe" (and yes, I spelled them wrong on purpose).

[minimender]

When I was a lad, 1000cc used to be called 10 horse power, so a 12 horse power would be 1200cc etc. Just a rough guide and I dont know where it came from.
Brake horse power is measured, so a 10 horse power engine would have different bhp depending on tune, it could have 50bhp or 150bhp depending on what it would pull on the machine.

My simple way of explaining.