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Originally Posted by mr0077
I thought the term applied to all HP readings since they all use a form of "brake" to measure torque and arithmetically determine HP from there...
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Not so! Rolling road dynamometers use an inertial mass that is accelerated by the engine spinning the driven wheels to determine horsepower from the rate at which the engine can actually accelerate the mass. So your brake dynamometer is using friction applied to the engine, whereas the rolling road uses an additional mass coupled to the engine, which are different principles.
Otherwise, brake horsepower measured by a brake dynamometer is the same a flywheel horsepower. Differences creep in when people begin to talk about SAE (Society of Automotive Engineers) or DIN (Deutsches Institut für Normung) horsepower, which are measured according to different test protocols, engine ancillary loads, etc.
When I was at college, I ran a series of experiments on reformulated gasolines on an engine running on a test bed, connected to a brake dynamometer. Some use a simple rope tied around the flywheel, whilst others use friction clutches or even hydraulic systems (like a torque converter but permanently stalled) to measure torque. Then, basically, torque times speed equaly horsepower.
Hope this helps!
Paul
