29 replies to this topic

[Ross Stonefeld]

Where does the 'brake' in BHP come from?

[rdrcr]

Horsepower and brake horsepower are different. Essentially, 1 horsepower is roughly equivalent to 100cc. Thus 16hp would be about 1.6 litres. However, a 1.6 engine wouldn’t be a 16 brake horsepower engine because the measurements are made differently.

Brake horsepower is measured by taking a drum filled with a fluid and attaching that to an engine. The power required to turn the drum is the brake horsepower - as the drum is ‘braked’ by the fluid.

I found a quick referrence site that is pretty cool. It shows more of these basics. Like HP & Torque, Volumetric Efficiency, RPM vs. MPH etc.

http://www.pro-flow.com/mustmath.htm

[Ross Stonefeld]

Wicked...


Im hoping that when cars are talked about in HP figures, they are using either HP or BHP and that some arent in one and others in another?

[desmo]

One horsepower is the work done at the rate of 550 foot-pounds per second and it is equivalent to 745.7 watts.

[ehagar]

Hmmm... this doesn't sound right. I used to know the answer, now I have to give it a think.

I believe it has something to do with the difference in indicated and brake ratings.

What's a brake rating?

Well, when you put a bike or car on a dyno, you aren't exactly directly measuring horsepower, but you are gauging torque. You are measuring the torque reaction against the mounts. If you know the RPM (pretty easy to do), you can then calculate the horsepower.

But the principle of a dyno is to provide resistance to the rotation of the crank, or to act as a brake against it... so hence the term, brake horsepower.

But wait, there is more! Ever heard of IMEP and BMEP? That is indicated and mean effective pressure. The difference is indicated doesn't account for internal losses such as engine friction....

I vaguely think of HP as a theoretical value, while BHP as the value that gets driven from the wheels after all the sources of resistance... probably wrong, but to be sure I'd have to dive back into my Engineering books.... I will probably have those books until I die...

Didn't James Watt base the HP unit on theoretical work of pit ponies? Hmmm....

[rdrcr]

The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that strange, arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner!

And what doesn't sound right? My definition of BHP? When you speak of a dyno are we speaking of a forces against a drum, where a measurment is taken of resistance?

[kodandaram]

I am really interested about this ...well i know that BHP stand for Brake horse power but when i was say about 12 yrs old or something i read in a book some figures about the specifications of a car and the term BHP caught my eye ...ever since i had beeb asking people what it stood for and you will be amused that most people told me that it stood for "British Horsepower " is it true ? i don't think so
So then i referred to a book called " Basics in Engine Dynamics" where it said BRAKE horsepower.But i also came across another unit termed PS (its a german word abbreviated..something like Preforde Shtode'..i guess) it stands for German Horse power it says ..and now it also says that 1ps = 0.98 BHP so you see it counts a lot when speaking 850 bhp.

But i still don't understand why the term BRAKE ? can anyone of you explain it in a aimpler way ?

[ehagar]

Actually, looking at it again, nothing really wrong at all.... the HP bit sounded a bit funny (I haven't heard of it, although visions of MEP, PLAN, , and a few other equations are bouning in my head....), while the BHP part sounded right... I guess our definitions are really identical. Dyno or Drum (or brake) are esentially the same thing....

As for the HP unit. I thought it was based on pit ponies!

[confucius]

The term "Brake Horsepower" comes from a type of dynamometer known as a Prony Brake Dynamometer. This type of dyno uses a mechanical brake with a torque reacting arm of known length that pushes on a scale to measure torque.

http://www.eng-tips....d/407/qid/10470

[ehagar]

Exactly... the principle of the Brake Dynamometer is to provide a resistance to rotation of the engines crankshaft, or to act as a brake against it.

[Top Fuel F1]

Originally posted by Top Fuel F1
HP is calculated, BHP is measured on the Dyno. See some info on them:
http://www.hyperdyno.com/what.htm
Rgds;

[rgagne]

here is my 2 cents...

I used to work as quality control manager in a diesel engine rebuilding shop. We had and were selling dynamometers.

We were using specially designed "water pump" as a mean to brake the engine, measuring the torque by the mean of a "torque arm" of known lenght pressing on a load sensor (an electronic balance).

By restricting the water outlet, the impeller of the pump tends to rotate the pump housing with it, which rotation is prevented by he torque arm...

you calculate the BHP with a simple formula: torque times rpm divided by 5250.

Very simple indeed...

you can see what the setup looks like here:
Taylor dynamometer

RGagne

[nick stone]

The German "PS" means Pferde Starke - literally Horse Power.
I think.

[leegle]

The simple Horse Power used by the British etc to tax cars is based purely on the bore of the engine. It dates back to steam engines and while I don't know the full details I think it is a simple transference of steam engine technology to internal combustion engines. In Australia during WW2 there was severe petrol rationing and anyone with a Chev 4 did well because the car had a good size bore and thus got more petrol because of its higher HP rating and relatively good fuel economy.

[BertlF]

Originally posted by nick stone
The German "PS" means Pferde Starke - literally Horse Power.
I think.

You're right. PS = Pferde Staerke (= Horse Power). The word 'Horse Power' comes from an early way to determine work. 1 PS (or HP) = the work of a horse pulling a certain weight over a certain distance. I don't know the exact values by heart but I can read it up later at home. Since the implementation of Standard International Dimensions (SID) PS (HP) has been replaced by Kilowatt (kw). However, due to the fact that power of car engines had been described in PS/HP for a long time (for example, the power of electric motors has always been expressed in kw), the PS/HP value is still predominant.

I've no idea about the value of BHP resp. the difference of HP/PS and BHP - sorry...

Bert

[desmo]

The terms horsepower and brake horsepower are now used interchangably. One is the expression of a unit of work, the latter the measured quantity expressed in the former unit.

[100cc]

Originally posted by rgagne


you calculate the BHP with a simple formula: torque times rpm divided by 5250.

........this means that torque and hp are the same at 5250RPM.

[marion5drsn]

According to my Handy Dandy multipliers for Engineers 1 HP = 42.44 B.T.U./min. or 33,000 Foot-lbs./min or 550 foot-lbs/sec or 1.014 metric horsepower or 10.70 Kg.-calories / min. or .7457Kilowats or 745.7 Watts. Also my old book Audels shows a picture of a very old Prony brake, a very crude instrument of horsepower measurement. It was a very large external drum brake with arms attached to a weight scale. Also water sprayed onto the hot surface to keep it cool. Just who was Prony is not given. Yours M.L. Anderson

[desmo]

Gaspard Clair Francois Marie Riche de Prony(!)

[Wolf]

To answer Kodandaram's question, You have been corrected on the correct German term for HP, but You are right about difference between SI HP (PS, as Germans refer to it) and is widely accepted in non-english speaking countries which is 735.499W and anglo-saxon HP which is 745.7W... That's why somebody observed (and Don Capps in his RVM on '61 GP season, IIRC) that 'Italians had smaller horses (compared to the Brits)' or something to that effect when commenting declared output of Dino 156 engine.

In automotive use BHP and HP are perfectly interchangable units and should be taken as engine output power with all devices attached which are normally used (except in case of Japanese manufacturers who declare engine power w/o ..., hence the BHP figure for the same engine measured by Japanese standards would be slightly higher than that of, say, European manufacturer*). Note should be taken that those figures represent engine output, not gearbox output.

* it has been reported that certain Japanese manufacturers not only had ventilators for cooling air driven by another engine (same type, synchronized with the engine whose output was measured), but fuel pumps & all other 'auxiliary' devices. I am not sure whether same driving technique was implemented on camshafts of the tested engine or not...

As someone said- just my 2¢ worth.;)

[kodandaram]

But are F1 figures measured in BHP or PS ? coz u know as i said 1PS = 0.98BHP and that means that 800PS = 784 BHP
So if BMW say they have 850 they must mean 850 PS ain't it ? also BMW is German ...so why have a british unit when you have a german driver and a german engine ?
Also it makes sense , i think 850 BHP is stupid thats too much : 850 PS would equate to 833 BHP which is a bit acceptable for end of season

[desmo]

I don't think there are any "official" BHP figures for F1. All we have are a handful of somewhat cryptic anectdotal quotes and a lot of guesswork. When you see an F1 engine on the dyno, they seem to be running the major ancillaries, pumps and alternator, on the engine's power.

[imaginesix]

Does anybody know how the old hp rating was calculated, and how it relates to kW?
I am referring to old hp figures where 15 was considered a high-powered auto, and some could get by with as little as 2 (Citroen 2CV). CV=Chevaux-Vapeurs (Horsepower)
I believe they still use this rating system in France to determine different vehicle's insurance rate.
Does this mean anything to anybody?

[desmo]

It appears that no one (including the French) know definitively how the French/Swiss CV "fiscal horsepower" ratings are precisely arrived at. It is tax law at it's least transparent and most arcane. Please refer to the applicable 1956 and 1977 circulars for more obfuscatory language.

[marion5drsn]

http://www.lycoming....n.com/main.html Go to search and then Watts.

An interesting article about how Watts cme up with ,"Horsepower.".

[bergwerk]

Originally posted by desmo
It appears that no one (including the French) know definitively how the French/Swiss CV "fiscal horsepower" ratings are precisely arrived at.

The fiscal rating of the French Cheval Vapeur is indeed a tricky one.

The formula for the calculation of the "Puissance Administrative/Fiscale" for passenger cars under 9 seats: Pa=m(0.0458 x C/K) 1.48

Whereby m is 1.0 for gas engines and 0.7 for diesel engines, C is displacement in cm3 and K is the average of the speeds in each gear at 1,000 rpm.

[imaginesix]

Oh.
My.
Gawd.

You have got to be kidding. If ever one needs an example of bureaucracy, there it is. But thanks anyways bergwerk.

You are being serious, aren't you?

[bergwerk]

Originally posted by imaginesix
You are being serious, aren't you?

Afraid so but here is the latest and much simpler formula for new passenger cars after 1.1.1999:

Pa= (CO2/45) + (P/40) where P is engine power in kW.

One notes that gas and diesel engines are no longer treated differently.

[AS110]

Under SI,horsepower is no longer a valid term,the Watt is the unit of power,inches,pounds,and gallons are no longer used as well.

Without reading your profiles,I would guess these posters are from Great Britain or the USA,two nations very reluctant to give up on very difficult to work in units of measurements.

Of course my brain still seems to like HP as a means of guaging how powerfull a motor is.As mentioned above,horsepower is not a measurable unit,torque is measured,and horespower calculated by the ''formula''.The modern dyno does this with software,the nerd has moved from sliderule to keyboard.

[AS110]

For those who think a dyno is an engine sceaming in a concrete room,with guys in white coats and clip boards looking through the window.Or the bay at the garage where they tied your car down and gave it a near death expeience,check out this.
http://www.charm.net...yno/dynokit.htm

So,your video camera is now a dyno,eeh,by gum.

I've told Santa I want the Road dyno,but we are still in negotiation.NO ONE is coming down MY chimney in a RED suit!
And he won't wear the silver suit I had made for him. No,honestly,silver is not my colour - Get a life fat man!!

He thinks - I'm Santa you MUST let me in!