I friend of mine and I have wagered a beer. I say that current OEM horsepower ratings are measured at the flywheel. He claims that the new ratings are at the rear wheels. Who wins?

 

Are you sitting in a bar now?

 

Well the rated 505hp z06 usually puts down ~460rwhp.

 

HP measured at the crank for most cars.

 

at the flywheel including accessories[waterpump/alt/p/s]

 

Crank. EXCEPT the Fbody which was factory underrated and is really rated ~rear wheel hp.

 

You win. Can we get in on the free beer too? As an "advisory" fee of course.

 

Technically speaking, you are correct. HP ratings from the factory are flywheel, whether they are optimistic or conservative is only conjecture. He is probably thinking that they put the cars on a chassis dyno and of course that's what everybody measures from AFTER the factory. Any chassis dyno measurements are rwhp.

 

Horsepower ratings have always been measured at the flywheel. Before 1971 whey were just measured without all the engine accessories mounted, so horsepower ratings were higher than they would be when the motor was installed in the car.

The fine print from Wikipedia, if you're interested:

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).

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 underrated.

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.

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).

How 'bout that?! Learn somethin' new every day...

 

YOU WIN!!!!!!!!!!! I have a 2002 Z06,,,,the advertised HP is 405. I dyno tuned the engine before i added mods ( headers and VARARAM) and REAR WHEEL HP was less a LOT less than the advertsed 405 HP!!

Go collect on your bet!!!!!!!!!!!!!!

BC

 

Have another!! You Win