Horsepower

[Sowellman]

In the U.K., the R56 Cooper is listed at 120 bhp and the MCS at 174 bhp. In the U.S., they list at 118 hp and 172 hp. Is that strictly the difference between two different measures of horsepower, or is there an actual difference in the engines delivered to the two countries?

[rayb]

I think it's usually because the US cars have a slightly different tuning to satisfy the tougher emmisions regulations in the US.

[kevkbuk]

I wouldn't worry, your not gonna feel 2bhp!

[Juno]

I'm reasonably confident that the engine is just the same, but the standards used for measurement differ (slightly)... Some markets call for measurement of horsepower at the flywheel and disregard losses caused by the water pump and other ancillaries, and some markets consider these and/or drivetrain losses too.



Pete

[Paul]

Brake horsepower (bhp)

Brake horsepower (bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump and other auxiliaries. Thus the prefix "brake" refers to where the power is measured: at the engine's output shaft, as on an engine dynamometer. The actual horsepower delivered to the driving wheels is less. An engine would have to be retested to obtain a rating in another system. The term "brake" refers to the use of a band brake to measure torque during the test (which is multiplied by the engine speed in revs/sec and the circumference of the band to give the power).

[edit] hp (SAE)

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 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 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.

Because SAE gross ratings were applied liberally, at best, there is no precise conversion from gross to net. Comparison of gross and net ratings for unchanged engines show a variance of anywhere from 40 to 150 horsepower. The Chrysler 426 Hemi, for example, in 1971 carried a 425 hp gross rating (often considered to be underrated) and a net rating of 375 hp.

[edit] SAE-certified horsepower

In 2005, the Society of Automotive Engineers introduced a new test procedure (J2723) for engine horsepower and torque. The procedure eliminates some of the areas of flexibility in power measurement, and requires an independent observer present when engines are measured. The test is voluntary, but engines completing it can be advertised as "SAE-certified".

Many manufacturers began switching to the new rating immediately, often with surprising results. The rated output of Cadillac's supercharged Northstar V8 jumped from 440 hp (328 kW) to 469 hp (350 kW) under the new tests, while the rating for Toyota's Camry 3.0 L 1MZ-FE V6 fell from 210 hp (157 kW) to 190 hp (142 kW). The first engine certified under the new program was the 7.0 L LS7 used in the 2006 Chevrolet Corvette Z06. Certified power rose slightly from 500 hp (373 kW) to 505 hp (377 kW).

[edit] hp (DIN)

DIN horsepower is the power measured according to the German standard DIN 70020. It is measured at the flywheel, and is in practical terms equivalent to the SAE net figure. However, be aware that DIN "horsepower" is often expressed in metric (Pferdestärke) rather than mechanical horsepower.

[edit] hp (ECE)

ECE R24 is another standard for measuring net horsepower. It is quite similar to the DIN 70020 standard, but the requirement for connecting an engine's fan during testing varies. ECE is seen as slightly more liberal than DIN, and ECE figures tend to be slightly higher than DIN. John Deere is one strong adherent to ECE testing.

[edit] 9768-EC

9768-EC is a standard from the European Union. Generally, ISO-14396 and 9768-EC metrics are very similar.

[edit] ISO 14396

ISO 14396[4] is a new method from the International Standards Organization for all engines not intended for on-road use. Generally, ISO-14396 and 9768-EC metrics are very similar. New Holland is an adherent of ISO-14396 testing.

From Wikipedia.

[Sowellman]

Quote: Originally Posted by Paul Mullett (original)

Brake horsepower (bhp)

In 2005, the Society of Automotive Engineers introduced a new test procedure (J2723) for engine horsepower and torque. The procedure eliminates some of the areas of flexibility in power measurement, and requires an independent observer present when engines are measured.

Again, this time in English.

Paul, thanks for the explanation.

[MINIAC]

Horsepower figures in Europe are "metric" horsepower ...

1 "metric" horsepower = 0.986320073 US pony

[KenL]

Quote: Originally Posted by MINIAC (original)

Horsepower figures in Europe are "metric" horsepower ...

1 "metric" horsepower = 0.986320073 US pony

Euro cars often quote a fancy German unit (ps), no idea if it is related to HP at all.

[MINIAC]

pferdestärke (ps) is "metric" horsepower