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PS versus BHP



from   http://www.fwkc.com/encyclopedia/low/articles/h/h011001344f.html


HORSEPOWER, unit of power in the English system for measuring the rate at which
an engine or other prime mover
 can perform mechanical work. It is usually abbreviated hp. Its electrical
equivalent is 746 W, and the heat equivalent is
 2545 Btu. One horsepower was originally defined as the amount of power
required to lift 33,000 lb 1 ft in 1 min, or 550
 ft-lb per sec. 

 The British engineer and inventor James Watt established this value for the
horsepower after determining in practical
 tests that horses could haul coal at the average rate of 22,000 ft-lb per min.
He then arbitrarily raised this figure by a
 factor of one-half to establish the current value. In the metric system, 1 hp
is sometimes called force de cheval or
 cheval-vapeur and is defined as 4500 kg-m per min, which is equivalent to
32,549 ft-lb per min, or 0.986 of the
 English horsepower unit.

	<this probably explains the difference between PS and BHP> ... Jim

 Three different horsepower values are used to quote the performance of an
engine: (1) Indicated horsepower is the
 theoretical efficiency of a reciprocating engine, which is determined from the
pressure developed by the cylinders of
 the engine; (2) brake or shaft horsepower is more commonly used to indicate
the practical ability of the engine, or the
 maximum performance, which is the indicated horsepower minus the power lost
through heat, friction, and
 compression; (3) rated horsepower is the power that an engine or motor can
produce efficiently for sustained periods
 of time. 

 Electric motors are capable of surges of power far in excess of their rated
horsepower (see ELECTRIC MOTORS AND
 GENERATORS). British automobile engines are classified in rated horsepower,
but their brake horsepower may be four
 to six times the rated horsepower. The power output of American automobile
engines is quoted in brake horsepower,
 most being rated between 60 and 200 hp.

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