Showing my ignorance I know but where does "brake horse power" come from?
My bike is 95bhp - does it mean it could drag 95 horses down the road? Seems a bit improbable. Has anyone tested this claim by the manufacturers?!
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It's all to do with the power required to lift a certain weight a certain height off the ground - that is what I remember seeing on a program anyway.
In fact, just found it:
"The term horsepower has been around since, well, the days when horses were doing the work of today's internal combustion engines. Rather than getting into the nuts and bolts here, suffice it to say that when James Watt coined the term "horsepower" it related to the weight of coal a horse could raise a particular distance up a mine shaft in a given amount of time - for example lifting 550 pounds of coal 100 feet in one minute, 55 pounds 1000 feet in one minute, and so on."
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And the BRAKE is there because it's measured against a brake on a dynomometer to load the engine.
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And if you prefer power outputs in (kilo)Watts: 1 hp = 746 Watts!
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And when James Watt did his work, he found that his engines were so much more powerful than a horse, that if he tried to sell them at their true rating, the mine owners would not believe him. So he artificially increased the power of a horse. If a horse was put on a brake, it would probably produce about 3/4 of a horsepower.
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Are you sure? IIRC, a human can produce about half a horsepower, e.g. on a bicycle. Not for very long, I grant you...
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Once upon a time I could have quoted the number of pounds lifted so far in a minute, but age dulls memory and Google is no help.
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Well, according to the Rubber Handbook, one horsepower is the amount of work needed to lift 33,000lbs one foot in one minute.
One horsepower is about 746 Watts.
Now, just to confuse matters there is more than one horsepower. You can have International, electric, water and metric. They are all about the same to 2 decimal places or so. Isn't metrology a wonderful thing.
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And the BRAKE is there because it's measured against a brake on a dynomometer to load the engine.
It also means that it is measured at the output shaft of the engine and is therefore not the power available at the driving wheels which will be somewhat less because of friction losses in the gearbox, transaxle, rear axle etc. It may also be for a bare engine not fitted with auxilliaries such as power steering pump, water pump, aircon pump etc.
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L\'escargot by name, but not by nature.
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Aren't most dynamometers rolling roads, i.e. measuring the power at the wheels? I know manufacturers do it at the engine, but that's just to make the figures look good.
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Aren't most dynamometers rolling roads, i.e. measuring the power at the wheels? I know manufacturers do it at the engine, but that's just to make the figures look good.
But aren't manufacturers generally the only source of engine power output information anyway?
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L\'escargot by name, but not by nature.
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"But aren't manufacturers generally the only source of engine power output information anyway?"
In most cases, yes, but when it's an engine/vehicle with some performance or tuning potential, then the figures bandied about tend to be from the wheels, which is a lot more meaningful (as well as being the only easy way to do it, of course!)
I suppose as long as the figures quoted are comparable, it doesn't matter too much. You don't hear the term 'Japanese horses' so much these days, anyway. Or perhaps we're just not allowed to say it... :-)
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Or, to put it another way, if you want to know how much power your car makes, the only practical method is to put it on a rolling-road dyno. Be prepared for disappointment, though - the auxiliary equipment and transmission losses are surprisingly high.
I remember Honda claiming about 105hp for their 6-cylinder CBX motorbike when it came out, and not being best pleased when the American 'Cycle' magazine could only get 86hp at the back wheel!
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>> It may also be for a bare engine not fitted with auxilliaries such as power steering pump, water pump, aircon pump etc. --
I'm sure it doesn't include the power steering pump or aircon pump, but I think you're right about the water pump, it's not required for engines measured for SAE bhp, but it is required for DIN bhp.
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<<...... but it isrequired for DIN bhp.
Shouldn't that be DIN ps?
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L\'escargot by name, but not by nature.
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<<...... but it is >> required for DIN bhp. >> Shouldn't that be DIN ps? --
PS = PferdeStarke = Horsepower
I always thought that SAE HP was without pumps, alternator etc. DIN was with those items operating.
Typically 100HP DIN = 115HP SAE.
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I love this place - I've always wondered about measuring at the engine v wheels and what the 'b' in bhp was about.
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I always thought that SAE (Silly American Estimate) was measured at the crankshaft, whereas DIN (Probably something in German) was measured at the back wheel(s).
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