What does BHP mean

[CorvetteMan]

My friend says it stands for back-end horsepower, but I say it stands for brake horsepower.Please tell me what it stands for.

[V.S.]

some voice in the back of my head tells me you're right. I don't know why it would stand for brake horse power, but I'm pretty sure it does.

[MBTN]

Brake Horse Power is correct. By brake, they mean at the crank, or what the engine is making. By the time the power reaches the wheels, it's down maybe 15-20%

[ivymike1031]

an article that you may find interesting: http://www.pumaracing.co.uk/power1.htm


As it has already been stated, bhp usually stands for "brake horsepower," which differentiates it from the theoretical (frictionless) "indicated horsepower" that you would calculate based on cylinder pressure alone.

I'm curious - when your friend said "back horsepower," was he contrasting that to "front horsepower?" So only rear-wheel drive cars would have BHP, or something like that?

[CraigFL]

Actually, BHP or "Brake Horse Power" is the horsepower measured with a "Braking" device that dissipates power. In the early days (real early!!0, it was a Prony Brake which was essentially a leather band stretched around the outside of a wheel. Now we use water, electric or friction type brakes to dissipate the power. BHP can be measured at the flywheel or at the rear wheels. Since there is no standard governing the measurement of BHP, it could mean just abou anything. Standards like ISO and SAE do specify how HP is to be measured.

[ivymike1031]

well yes, that's how it's measured... Since your response "actually..." implies that my explanation was wrong, perhaps you can answer this question better than I did:

Why do they call it "brake horsepower" instead of just "horsepower?" Are there other kinds of horsepower about an engine?

[CraigFL]

Originally posted by ivymike1031
well yes, that's how it's measured... Since your response "actually..." implies that my explanation was wrong, perhaps you can answer this question better than I did:

Why do they call it "brake horsepower" instead of just "horsepower?" Are there other kinds of horsepower about an engine?

I usually quote if my response is directed at a specific entry, otherwise I just respond to all the previous entries -- I wasn't implying you were wrong But... I said "actually" because the previous answers had not stated definitivly that it was something that was measured with a device called a brake.

They call it "brake" horsepower because it was actually measured at some point-- giving credibility to the number. It suppose it could be "calculated"(using thermodynamic theory), "observed" (running 0-60 times) or even "estimated"(similar engine types).

[ivymike1031]

the term I referred to, "indicated horsepower," is pretty close to what I think you mean when you say "calculated by thermodynamic theory." Indicated horsepower is the power that would be produced by an engine with no losses outside of pumping losses. It can be calculated directly from a cylinder pressure trace (if engine geometry is known), or estimated reasonably well via simple thermodynamic equations over an ideal engine cycle (ie: Otto cycle w/ polytropic compression and expansion, ideal combustion, etc).

It's my understanding that they call it "indicated horsepower" because they used to have a mechanical device for measuring cylinder pressure vs piston position, which would trace out a P-V diagram on a sheet of paper, thus "indicating" the power output of an engine (not counting mechanical and hydrodynamic losses). Originally used for steam engines, if memory serves.

[Jay!]

I always understood it to be an indication of where the HP was measured. In my mind, the alternative to Brake HP is Flywheel HP, the difference in which will be the drivetrain inefficiency. In this way, both figures are measured, not calculated.

[ivymike1031]

The idea being that "brake horsepower" is measured at the vehicle's brakes? Sorry, I'll have to disagree with that one.

When someone mentions "flywheel horsepower," he's talking about brake horsepower for the engine alone (as tested on an engine dyno). If he mentions "horsepower at the wheels," then he's still talking about brake horsepower, but this time measured at the wheels (chassis dyno).

[ivymike1031]

here's a fun quiz that I found:
http://www.dieselpage.com/trivia5.htm

and another cool page that's not so related to this discussion:
http://www.tpub.com/engine1/

and one that attempts to answer the BHP question posed here (but fails miserably)

http://www.sciencenet.org.uk/databas...3/p01446d.html

[texan]

To put it simply, brake horsepower (aka bhp) is just an old term left lying around that now commonly refers to SAE net engine output. Go into detail on the background of the term all you like, talk about thermal and drivetrain efficiency to your heart's content... the simple truth is that it's an overused acronym for something that basically means SAE net output at the crank. In other words, it's the same standard to which current manufacturers publish their engine power ratings. Chassis dynomometer readings check output to the wheels, engine dynos check output at the flywheel. Depending upon what necessary ancillaries are strapped onto the engine at such time of an engine dyno reading, this may or may not be the SAE bhp output.

[ivymike1031]

jeez, sometimes I feel like a dun-bass.
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