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Old 01-09-2013, 10:19 PM
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What exactly is "Brake horse power"?

My son asked me a big ago and I couldn't answer it. In looking it up on the net it looks the same as just "horse power", what is the difference?

Brian

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Old 01-09-2013, 10:35 PM
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its hp at the flywheel/flex plate , just a way of defining if ur talking about engine hp or power at the tires since chassis dynos are common now
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Old 01-09-2013, 11:52 PM
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Quote:
Originally Posted by MARTINSR View Post
My son asked me a big ago and I couldn't answer it. In looking it up on the net it looks the same as just "horse power", what is the difference?

Brian
I could be wrong, but....I don't think there is a difference anymore, but there used to be.

As I understand it, brake horsepower means actual, measured, proven horsepower.

In the early days of gas and steam engines, horsepower ratings were calculated by plugging the engine's dimensions into a mathematical formula. It wasn't a measure of the engine's peak horsepower but the power the engine could be expected to produce continuously.

With the invention of the Prony Brake in 1821, it was possible to measure the actual horsepower output of an engine. Engineers used the term 'brake horsepower' to indicate that it was the result of an actual performance test, rather than an estimate.

Any horsepower measured on a dynamometer is brake horsepower, but most people now just call it horsepower.

Just for fun, here's a video of a Prony Brake demonstration at an antique tractor show.


Hope this helps....

Joe G.
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Old 01-10-2013, 02:20 AM
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"Brake HP" is now recognized as the power measured at the flywheel, but a brake can be used to measure output at the rear wheels or at the flywheel.

The first dynos used water to absorb and dissipate the energy of the engine. The water acted as a brake (why they are called water brake dynos) to counter the engine's force at the crank.

Now there are other types of dynos that don't use water or any other liquid meduim, but they do the same job, and their results can also be called brake HP.
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Old 01-10-2013, 08:07 AM
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Thanks guys, it's pretty rare when dad does't have the answer right?

Brian
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Old 01-14-2013, 08:37 PM
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Of course you have to remember that - no matter how it is measured - horsepower is a bit of a fictional number anyway. It is TORQUE that gets measured and "horsepower" is then calculated from that.

To get HP you need to know the measured torque and the RPM each torque number was measured at

HP is the Torque(in pounds/feet) times RPM, divided by 5252

By the way - any time you see a hp & torque graph where the lines do not cross at 5252 RPM, I get just a teeny bit suspicious

What was REALLY fun was calculating the torque for an antique steam engine I saw at a fairgrounds recently. The plaque said it made 500 hp at 500 RPM.

Do the math and get your mind blown by the humongous torque that monster had!
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Old 01-14-2013, 09:24 PM
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A wiki article on dyno's

Dynamometer - Wikipedia, the free encyclopedia

Sam
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