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Difference between revisions of "Horsepower"
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==Definition== | ==Definition== | ||
There have been many definitions for the term over the years since [[James Watt]] first coined the term in | There have been many definitions for the term over the years since [[James Watt]] first coined the term in 1782. The following metrics have been widely used: | ||
* [[#Mechanical horsepower|Mechanical horsepower]] — 0.74569987158227022 [[watt|kW]] (33,000 ft·lbf per minute) | * [[#Mechanical horsepower|Mechanical horsepower]] — 0.74569987158227022 [[watt|kW]] (33,000 ft·lbf per minute) | ||
* [[#Metric horsepower|Metric horsepower]] — 0.73549875 kW | * [[#Metric horsepower|Metric horsepower]] — 0.73549875 kW | ||
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In the United States the term "bhp" fell into disuse after the American [[Society of Automotive Engineers]] (SAE) recommended manufacturers use '''hp (SAE)''' to indicate the net power of the engine, given that particular car's complete engine installation. It measures engine power at the [[flywheel]], not counting drivetrain losses. | In the United States the term "bhp" fell into disuse after the American [[Society of Automotive Engineers]] (SAE) recommended manufacturers use '''hp (SAE)''' to indicate the net power of the engine, given that particular car's complete engine installation. It measures engine power at the [[flywheel]], not counting drivetrain losses. | ||
Starting in | Starting in 1971 automakers began to quote power in terms of '''SAE net horsepower''' (as defined by standard J1349). This reflected the rated power of the engine in as-installed trim, with all accessories and standard intake and exhaust systems. By 1972 U.S. carmakers quoted power exclusively in SAE net hp. The change was meant to 'deflate' power ratings to assuage the [[auto insurance]] industry and environmental and safety lobbies, as well as to obfuscate the power losses caused by [[smog|emissions]]-control equipment. | ||
SAE net ratings, while more accurate than gross ratings, still represent the engine's power at the flywheel. Contrary to some reports, it does ''not'' measure power at the drive wheels. | SAE net ratings, while more accurate than gross ratings, still represent the engine's power at the flywheel. Contrary to some reports, it does ''not'' measure power at the drive wheels. | ||