Engine power measurments
Thread Starter
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
Engine power measurements
I've started hanging out/drinking beer with a guy that's on my pool league team and his friend. Both of them are cool guys and carheads just like me so we get along fine. The unusual thing is, they're both diehard Buick people. They both own Turbo cars. In addition, one owns a show-quality early 70s Riviera and the other one has a GS Sun Coupe.
I brought the vette over to one of them's house the other evening after work. We were drinking beer and talking about cars when one of them says that since the early 70s, all published GM HP and torque ratings for production cars were rear-wheel measurments. I always read that GM (and all other manufacturers) measured this at the flywheel, be it gross or net, so of course I disagreed with both of them. All 3 of us got into a fistfight. Ha! Just kidding. We did disagree the point for several minutes though. I want to take something back to them that proves GM never published HP and torque ratings from measurements taken at the rear wheel.
Brett
I brought the vette over to one of them's house the other evening after work. We were drinking beer and talking about cars when one of them says that since the early 70s, all published GM HP and torque ratings for production cars were rear-wheel measurments. I always read that GM (and all other manufacturers) measured this at the flywheel, be it gross or net, so of course I disagreed with both of them. All 3 of us got into a fistfight. Ha! Just kidding. We did disagree the point for several minutes though. I want to take something back to them that proves GM never published HP and torque ratings from measurements taken at the rear wheel.
Brett
Last edited by Brettmc; Mar 10, 2006 at 12:00 PM.
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
When Chevrolet made the switch back around 1972, they switched to net horsepower. The net horsepower was not measured at the rear wheels, rather, it was measured at the flywheel WITH ALL OF THE ACCESSORIES.
Melting Slicks
Joined: Apr 2004
Posts: 2,083
Likes: 2
From: Montreal Qc.
Here you go:
from http://www.answers.com/topic/horsepower
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 power of the engine, given that particular car's complete engine installation. It measures engine power at the flywheel, not counting drivetrain losses.
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.
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 power of the engine, given that particular car's complete engine installation. It measures engine power at the flywheel, not counting drivetrain losses.
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.
Pro
Joined: Sep 2004
Posts: 690
Likes: 0
From: Madison WI
No company would ever be foolish enough to publish RWHP/TQ numbers as advertised, since the vast majority of the population doesn't realize the difference.
And yes, it was a switch from gross to net HP, not gross to RWHP.
And yes, it was a switch from gross to net HP, not gross to RWHP.
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Originally Posted by 72Tornado
No company would ever be foolish enough to publish RWHP/TQ numbers as advertised, since the vast majority of the population doesn't realize the difference.
And yes, it was a switch from gross to net HP, not gross to RWHP.
And yes, it was a switch from gross to net HP, not gross to RWHP.
Also, could you imagine the number of people returning their vehicle to the dealer when their car would not dyno at the advertised hp at the rear wheels?
