HP ratings (pre 1971, 1972-2005, 2005 on)
#1
08-03-2007, 08:48 PM
HP ratings (pre 1971, 1972-2005, 2005 on)
From http://en.wikipedia.org/wiki/Horse_power
SAE gross horsepower (pre 1972)
Prior to 1972 most American automakers rated their engines in terms of SAE gross horsepower (defined under SAE standards J245 and J1995). Gross hp was measured using a blueprinted test engine running on a stand without accessories, mufflers, or emissions control devices. It therefore reflected a maximum, theoretical value, not the power of an installed engine in a street car. Gross horsepower figures were also subject to considerable adjustment by carmakers: the power ratings of mass-market engines were often exaggerated, while those for the highest-performance muscle car engines were frequently understated.
hp (SAE) net (1972-2005)
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, US 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 shows 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 understated) and a net rating of 375 hp.
SAE-certified horsepower (2005 on)
In 2005, the Society of Automotive Engineers introduced a new test procedure for engine horsepower and torque.[6] 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 440hp (328kW) to 469hp (350kW) under the new tests, while the rating for Toyota's Camry 3.0L 1MZ-FE
SAE gross horsepower (pre 1972)
Prior to 1972 most American automakers rated their engines in terms of SAE gross horsepower (defined under SAE standards J245 and J1995). Gross hp was measured using a blueprinted test engine running on a stand without accessories, mufflers, or emissions control devices. It therefore reflected a maximum, theoretical value, not the power of an installed engine in a street car. Gross horsepower figures were also subject to considerable adjustment by carmakers: the power ratings of mass-market engines were often exaggerated, while those for the highest-performance muscle car engines were frequently understated.
hp (SAE) net (1972-2005)
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, US 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 shows 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 understated) and a net rating of 375 hp.
SAE-certified horsepower (2005 on)
In 2005, the Society of Automotive Engineers introduced a new test procedure for engine horsepower and torque.[6] 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 440hp (328kW) to 469hp (350kW) under the new tests, while the rating for Toyota's Camry 3.0L 1MZ-FE
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