ZoomZoom

I know what wheel HP is, but what is the difference between HP and BHP? ...Thanks!

wakeech

there isn't any difference, just a difference in terminology....
bhp (or "brake horse power") is the way the british say it, and still referes to the horsepower the engine produces, but it is the amount of horsepower the "brake" on the engine is absorbing (and the engine is putting out to move the brake)...
oh, the brake on the dyno is the bit that creates the resistance the engine turns against, either at the wheel or at the crank... usually, when talking specifically about the engine, you're talkin' at the flywheel (chassis dyno), but can be applied to "at the wheel" horsepower. i ran into the same thing when i got into F1 and was reading all these british pages referring to "bhp", but it is the same as "normal hp" to my understanding.

ZoomZoom

Thanks for the quick reply! :D

Sputnik

Wakeech, you even confused me with that one.

"Wheel" HP, or RWHP (rear-wheel drive HP), or FWHP (front-wheel drive HP), etc. Is measured when a car is put on a rolling dyno, and the amount of power that the car puts down on the pavement (or at the driven wheels) is measured. This is more of a true measurement of how the overall car will perform.

BHP, or "brake" HP, is measured when the engine alone is put on a special dyno to measure what the engine alone puts out. This is the number that manufacturers give for the car's power. The is the 250 HP that the Renesis is supposed to have.

The Wheel HP number is normally around 20% less than the Brake HP, because the transmission and other drivetrain components (and sometimes the installed exhaust and intake components) eat up some of the power.

---jps

wakeech

:p yeah, i confuse myself... what i was trying to say is that "bhp" and "hp" are the same unit, just with the "brake" added in there for the brits...

evel333

Forgive my ignorance, but what about the "PS" that the Japanese use? Will someone please enlighten me.

Buger

[GLOW OF LIGHT]
A scottish dude named Watt figured that a horse could do 746 watts of work.

Germans estimated that their wimpier horses could only do 736 watts of work and they called their measurement Pferdestaerke or PS.

Conversion factor is approx 0.9866 PS = 1 HP ergo the 250 PS figure that Mazda originally put out has been translated to 247 HP.
[/GLOW OF LIGHT]


:D

wakeech

*looking in direction of brief errie halo*
guys, was that a UFO, or just an angel... where ever that voice came from, God or whomever, sure was f*ckin' brilliant, eh??

evel333

Wow. You are indeed a sage, Buger. I always figured it meant "Pony Strength" or something to that extent! (^_^) Thank you for the explanation.

Buger

:D Altavista Babelfish does translate Pferdestaerke to "horse power".

maxcooper

Chassis dynos like Dynojets often don't have a brake. Instead they have a big heavy drum that you accelerate with the car. These are called "inertial dynos" because the engine fights the inertia of the drum. HP is calculated from how fast the drum accelerates. Inertial dynos require that you accelerate to measure the HP -- you can't just sit at one RPM and take a reading.

Dynos with a brake (engine or chassis) allow you to hold the engine at one RPM and measure the HP.

Brake HP and the HP measured on a chassis dyno are different in this way.

There are chassis dynos that use a brake also. Big heavy wheels will reduce HP on an inertial dyno, but they would not be a factor on a dyno with a brake.

-Max

rglbegl

Glad I searched before asking this but . . . . .
I always thought that what the Brits called BHP ( Brake HP) was the power the car put out to its own brakes. Is it not the same thing as what we Americans call RWHP? I understand losing power from the tranny, but I am sure there is no power loss between the brakes and the tires. (except on the humvee )
Am I confused, or aren't they THE SAME THING?!?!?!?!?

Ike

Crank horsepower, brake horsepower, and just plain old horsepower as listed by the manufacturer are all the same thing.

DrDiaboloco

It's not just for the "Brits". Most US car magazines will list "bhp" in their articles and/or data panels.

So yes, bhp and hp are the same thing, assuming you're talking about engine dyno numbers. "Crank horsepower" is the same thing, too, but this term is almost completely unused in the mainstream, as the "crank" portion is assumed (as is the "brake" part in the instances where it is not used).

Ericok

Brake horsepower (bhp) is the measure of an engine's horsepower without the losses caused by the gearbox, generator, differential, water pump and other auxiliaries. The term "brake" refers to a type of dynamometer which uses a band brake to measure torque during the test. Modern engine dynamometers don't always use a "brake" to measure torque so the term BHP is used in the traditional sense. In the end, Ike may actually be right.

DrDiaboloco

He is right, and you're confused. BHP/HP, in the modern sense, is absolutely determined with all the accessories, intake and exhaust system attached (the gearbox and differential are obviously not engine accessories). What you are thinking of is the old "gross HP" measurement that American car makers in particular used to inflate the actual HP the engine would produce when installed in the car... And "gross HP" hasn't been used in at least thirty years.

The numbers we Americans see these days (and have, in varying levels of "truthiness", since the early 70's), is "SAE Net" hp (or bhp, if you will), with all accessories, intake, exhaust, engine computers, etc. installed. This number is meant to represent what the engine will produce in a car that is delivered to a customer, not what a handbuilt engine on a stand with a straight exhaust and no pumps/alternators/etc. attached will produce.

The recently-implemented newer standard for measuring SAE Net HP has been responsible for the dwindling hp rating of the RX-8 (and some cars as well), as the engine itself hasn't changed. The newest standard closed some loopholes that allowed some artificially high numbers to be quoted/published, that's where the 6hp went between '05 cars and '06 cars... The 12hp that disappeared between '04 and is another thing entirely.

Ericok

That's my point. I thought the whole discussion WAS about the old, traditional terminology NOT the new SAE horsepower calculation requirement (which includes accessories and the participation of an independent observer). The OP was asking about the origins of the term BHP, not SAE horsepower. You're answering a question he didn't ask.

saturn

If you believe Wikipedia:

SAE gross horsepower
Prior to 1972 most American automakers rated their engines in terms of SAE gross horsepower (defined under SAE standards J245 and J1995). Gross hp was measured using a blueprinted test engine running on a stand without accessories, mufflers, or emissions control devices. It therefore reflected a maximum, theoretical value, not the power of an installed engine in a street car. Gross horsepower figures were also subject to considerable adjustment by carmakers: the power ratings of mass-market engines were often exaggerated, while those for the highest-performance muscle car engines were frequently underrated.

Brake horsepower (bhp)
Brake horsepower (bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump and other auxiliaries. Thus the prefix "brake" refers to where the power is measured: at the engine's output shaft, as on an engine dynamometer. The actual horsepower delivered to the driving wheels is less. An engine would have to be retested to obtain a rating in another system. The term "brake" refers to the use of a band brake to measure torque during the test (which is multiplied by the engine speed in revs/sec and the circumference of the band to give the power).

As others have stated, As far as what the OP was asking, hp and bhp are the same thing -- horsepower measured at the engine flywheel.

DrDiaboloco

...and in this case, I do. It's consistent with what I, Ike, and others have stated.
Really? You're making up a question he didn't ask by adding into it "the origins of the term BHP", which is nowhere in his question or in any of his followup posts. My post was in relation to the string of answers that followed it, and specifically correcting YOUR statement that bhp is measured without engine accessories attached, which is categorically wrong.

saturn

Ok, you can't have it both ways. You say you agree with Wikipedia, but you told Ericok that he was "confused" when he essentially quoted Wikipedia exactly. Then you made a statement saying that what he was thinking about was the old "gross hp" measurement which was incorrect. Ike and Ericok are right. You're not. You don't need all the condescending italics and ellipses.

DrDiaboloco

I didn't read the whole wikipedia article... I skimmed the "gross hp" part and skipped the rest, assuming that that was the point of contention. So I guess I don't agree with it, as I (and no person measuring the HP of an engine with an engine dynamometer) never consider the "differential" and the "gearbox" to be "auxiliaries" of the engine, as they would always be found after the engine's output shaft (or flywheel or crank, same thing)

The METHOD of determining the actual hp/bhp of an engine is immaterial, as long as the method is described to you. The VALUE of said measurement is the hp/bhp value... If you strip off all the accessories and don't have a real-world exhaust system, and therefore come up with a bogus value for how it would perform in the car, you come up with a "gross" rating... Which is still depicted in terms of hp/bhp. If you use all the accessories, the intake, the exhaust system which will be on the engine as installed in the car, and meet the SAE protocol, you will come up with an SAE Net hp/bhp rating. The values are the different, but the SCALE is the same.

Either way, you are using the same gauge to determine the "horsepower" of the engine. Remember the old Ford 5.0 V8? Didja notice that somewhere between the mid-80's and the early-90's it lost something like 15-20hp? That is because they changed the testing method to more accurately represent the hp the engine would produce in a MUSTANG, not the test bench with all sorts of best-case scenarios to make a better number for their advertising. Same engine, lower hp. That was due to a change in testing method, just like the difference between Net and Gross twenty years prior. But... Still the same units... Those units being brake horsepower, or just plain horsepower, just fewer of them because the method of determining the number of them changed. Similarly, the RX-8, with no physical change to the engine, went from 238bhp to 232bhp due to a change in testing method. The "size" of the HP don't change from testing method to testing method, like Gross to Net, but the number of those horses change.

As Ike said, and you seem to believe him more than me, brake horsepower and horsepower are the same thing. That is a correct statement. Ericok stated that brake horsepower is determined by measuring an engine without the accessories attached. That is incorrect. I skimmed the wikipedia article quickly and agreed with it, and that, too, was incorrect. My bad. I apologize for giving you a headache.

I'm also sorry if stating the truth makes it look condescending, but when Ericok moves on and puts words in the OP's statements that aren't there, I don't know what to tell ya. What can I say, I'm the only bad guy here.

So... HP and BHP are interchangeable. They are the same thing. So is crank HP, as HP/BHP are measured at the crank... Even if they don't physically use a "brake" in the engine dyno in question, the measure of what a 1HP is and the measure of what 1BHP is are exactly the same. It has nothing to do with the testing method. Period. The reason I got into "gross HP" in the first place was because Ericok's description of BHP is actually the description of what gross HP is... Which, as I stated, isn't a "type" of horsepower at all, but a MEASUREMENT METHOD (and an archaic one) of determining it.

So, Saturn, since you say I'm wrong, point out where it is that I'm wrong... Aside from my gaffe of not reading the whole wikipedia article and agreeing with it.

supergoat

How does such a simple question get so many lengthy replies?

They are the same thing. End of story.

It's like asking what is the difference between pizza and a pizza pie. Nothing! Just different terminology.

Burf!

DrDiaboloco

Indeed. One could also argue about the term "foot-pounds" as we usually hear it, as opposed to "lb.-ft.", as it is always written. Same thing, but the way it's usually spoken is exactly the opposite of how it's written... And they mean the same thing.

In the US & Canada, "BHP", is restricted mostly to automotive magazines, which is where most of us have seen the term. Car and Driver and Road and Track, especially, use the term almost exclusively, even in the text of articles. The numbers they quote with the "BHP" suffix are the same numbers as the manufacturers quote for their vehicles as "HP" in their advertising and to the press. The only consistent difference in the mags is with vehicles that use the "other" methods of measuring HP, such as DIN (German), PS (Metric), JIS (Japanese), KW, etc. The auto mags mention those numbers as quoted from their sources instead of using common mathematical conversions, as the cars/trucks in question usually aren't US-market models, which would of course have their own SAE Net numbers if and when they make it stateside.

Of course there are all kinds of other HP numbers that have no relation to common automotive applications outside of the arcana of engineering, such as Indicated horsepower, Shaft horsepower, Equivalent Shaft horsepower, etc.

chris_abr

Brake Power (BP) - Engine's power measured at the crankshaft, on an output shaft (it is measured in Watts or kiloWatts).

Code:

Formula: Bp (kW) = [2 x Pi x Torque(Nm) x N(Revs/sec)] / 1000 (to convert to kW)

Brake Horse Power (BHP)- Car's power output measured at the wheel.

Horse Power (HP) - Basically, it is something like "newtonmeter". It is a way of measuring power. 1 horse power (HP) = 745.7 Watts.

Code:

Formula: HP= BP(in watts) / 745.7

So if you understand it well - Yes, the BHP(WHP) is the most important value, so you want to look at that, because it tells you the actual power output that you will get out of your car.

Quote:

Interesting fact - BHP(WHP) is usually about 20% lower than BP on a mainstream(family) car.

Source: Myself, Autosport/Automotive Engineering University Student - After reading a few books, this info taken from: Automotive Science and Mathematics First Edition (2008) by Allan Bonnick (pages: 158-160)

RIWWP

iTrader: (2)

Fixed


And you are even wrong in your post.

SAE HP is measured at the engine crankshaft power
BHP is measured at the flywheel (so usually slightly lower than SAE HP due to the added flywheel weight)
WHP is measured at the wheels (and significantly lower than SAE HP and BHP due to the rest of the drivetrain losses.

HP is a theoretical number that we attempt to arrive at using one of the standards above

All measurements are of the engine output, just measured at different points.


I basically don't care what source you have, if you use terms other than these on a car enthusiast forums you are going to cause confusion at best, get hammered at worst, and you won't be able to get your point across because you are using different definitions for the words typed than the people you are trying to talk to.