"Watt found by experiment in 1782 that a 'brewery horse' could produce per minute." James Watt and Matthew Boulton standardized that figure at per minute the next year. A common legend states that the unit was created when one of Watt's first customers, a brewer, specifically demanded an engine that would match a horse, and chose the strongest horse he had and driving it to the limit.


In the early days of steam use, the boiler horsepower was roughly comparable to the horsepower of engines fed by the boiler. The term "boiler horsepower" was originally developed at the Philadelphia Centennial Exhibition in 1876, where the best steam engines of that period were tested.


A few years later in 1884, the ASME re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 pounds per hour of water "from and at" 212 °F.


The atmospheric correction standards for barometric pressure, humidity and temperature for SAE gross power testing were relatively idealistic. ==== SAE net power==== In the United States, the term [horsepower (bhp)|bhp] fell into disuse in 1971–1972, as automakers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349.


This is equivalent to 735.49875 W, or 98.6% of an imperial mechanical horsepower. In 1972, the PS was rendered obsolete by EEC directives, when it was replaced by the kilowatt as the official power-measuring unit.


Watt, while aware of the trick, accepted the challenge and built a machine that was actually even stronger than the figure achieved by the brewer, and it was the output of that machine which became the horsepower. In 1993, R.


This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold. ====SAE certified power==== In 2005, the SAE introduced "SAE Certified Power" with SAE J2723.

For example, the 2006 Ford Five Hundred is rated at , the same as that of 2005 model.


The first engine certified under the new program was the 7.0 L LS7 used in the 2006 Chevrolet Corvette Z06.

For example, the 2006 Ford Five Hundred is rated at , the same as that of 2005 model.

However, the 2006 rating does not reflect the new SAE testing procedure, as Ford is not going to incur the extra expense of retesting its existing engines.


With the implementation of the EU Directive 80/181/EEC on 1 January 2010, the use of horsepower in the EU is permitted only as a supplementary unit. ==History== The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them.

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