Did manufacturers lie about Horsepower?

[Nightrage]

My stepdad has a 69 Z/28 RS Camaro. It says 290 horsepower on the hood. I've heard rumors that it actually pushed out over 325 horsepower but GM said it had less so insurance would be more affordable. I've also been told this was the case on almost all muscle cars. I've heard that the 79 Trans Am with the 6.6 liter V8 had around 300 horsepower but everything else i checked said it only has about 220 horsepower. Is their any truth to these rumors? I can't imagine a 6.6 only putting out 220 horses although i'd imagine it's possible due to the fuel crisis and emissions equipment choking it.

[Mirroredshades]

Yes and Yes. In the 60's and early 70's they were underestimating in a lot of cases.

By the late 70's and early 80's they were more accurate. They were so de-tuned and over emissioned that it took a 455 to make 200 HP.

My wife's Honda Civic would wax an early stock 80's Vette.

The 80 Vette with Crap-Fire Injection was rated at 185 HP. Can you imagine?

[Jeff_in_Atl]

This is what I was told years ago.

Back in the 60's and 70s there wasn't a standard as to how the manufacturers rated horsepower. Some rated it at the flywheel while others rated it at the wheels. I'm thinking it was in the mid 70's sometime when the government setup a standard J1369 (I think) as to how the manufacturers rated horse power. I think now they have to rate it at the flywheel and run it through an equation to estimate drive train loss.

My mom had a 1977 Mercury Grand Marquis with a 460 CID that put out 140 horses.

[Mirroredshades]

I wasn't going to muddy the waters between HP and BHP but since you started it.

Until sometime in the 70's, there was no real standard but HP was generally rated at the Flywheel. Early 80's (I think) they switched to brake horse power (BHP). This measured HP at a standard point, I think at the Wheels. It is more accurate because it takes into consideration the power loss from the transmission, axle, etc.

[Injuneer]

I'm going to disagree with both of you. Manufacturers have ALWAYS used flywheel HP, NOT rear wheel HP. Prior to about 1972 manufacturers used "GROSS" HP... they took a "blueprint" example of the engine, removed all the power equipment and accessories drives, and ran it on an engine dyno with an optimized air intake and exhaust setup. That, in effect measured the maximum flywheel HP the engine was capable of, but in no way, shape, or form measured the engine HP as intalled in the car, with all the little neccessary items like alternator, belts, power accessories, intake and exhaust constraints.

In 1972 (give or take a year), the g'ment determined that all engines would be rated "SAE NET"..... the engine was installed on an engine dyno exactly the way it would be installed in the car.... intake, exhaust, pulleys and "standard" driven power equipment. Now you were getting a realistic measure of what your engine would make AT THE FLYWHEEL in your car. The typical high performance engine lost about 100HP in this reconfiguration, although that was also a bit confused by the simultaneous addition of emissions control equipment, and the lowering of compression ratio to accomodate unleaded gasoline.

And "brake" HP does not refer to rear wheel HP... it indicates that the power measurement was taken on an "engine brake" type dynomometer.

[Fastbird93]

I'm going to disagree with both of you. Manufacturers have ALWAYS used flywheel HP, NOT rear wheel HP. Prior to about 1972 manufacturers used "GROSS" HP... they took a "blueprint" example of the engine, removed all the power equipment and accessories drives, and ran it on an engine dyno with an optimized air intake and exhaust setup. That, in effect measured the maximum flywheel HP the engine was capable of, but in no way, shape, or form measured the engine HP as intalled in the car, with all the little neccessary items like alternator, belts, power accessories, intake and exhaust constraints.

In 1972 (give or take a year), the g'ment determined that all engines would be rated "SAE NET"..... the engine was installed on an engine dyno exactly the way it would be installed in the car.... intake, exhaust, pulleys and "standard" driven power equipment. Now you were getting a realistic measure of what your engine would make AT THE FLYWHEEL in your car. The typical high performance engine lost about 100HP in this reconfiguration, although that was also a bit confused by the simultaneous addition of emissions control equipment, and the lowering of compression ratio to accomodate unleaded gasoline.

And "brake" HP does not refer to rear wheel HP... it indicates that the power measurement was taken on an "engine brake" type dynomometer.

You beat me to the punch!!

[Jeff_in_Atl]

I'm going to disagree with both of you. Manufacturers have ALWAYS used flywheel HP, NOT rear wheel HP. Prior to about 1972 manufacturers used "GROSS" HP... they took a "blueprint" example of the engine, removed all the power equipment and accessories drives, and ran it on an engine dyno with an optimized air intake and exhaust setup. That, in effect measured the maximum flywheel HP the engine was capable of, but in no way, shape, or form measured the engine HP as intalled in the car, with all the little neccessary items like alternator, belts, power accessories, intake and exhaust constraints.

In 1972 (give or take a year), the g'ment determined that all engines would be rated "SAE NET"..... the engine was installed on an engine dyno exactly the way it would be installed in the car.... intake, exhaust, pulleys and "standard" driven power equipment. Now you were getting a realistic measure of what your engine would make AT THE FLYWHEEL in your car. The typical high performance engine lost about 100HP in this reconfiguration, although that was also a bit confused by the simultaneous addition of emissions control equipment, and the lowering of compression ratio to accomodate unleaded gasoline.

I was at least partially right. I know that standard rating is J1369. It used to be the little asterisk in the HP rating in the sales brochures.

I'm still not sure there was a government standard before J1369. Maybe it was a gentleman's agreement but I don't think it was official or mandated like J1369 is now. I know the standard was updated in the early nineties. (I think it was 1993) Everybody lost HP when it did. The Mustang went from 225 to 215 even though it was the exact same motor.

[N20LT4Bird]

You beat me to the punch!!

Me too. Back in the day, it was a gross HP rating, but many cars were underrated. My GTO was rated at 350 Horse - but that 350 horse doesnt compare to today's 350 horse.

[Injuneer]

The original 350ci "LT-1" (note use of hyphen) appeared in the Corvette in 1970. CR was 11:1 and it was "gross" rated at 370HP.

In 1971, that engine dropped to 330HP with a 9.0:1 CR. That loss is emissions and CR related.

In 1972 it was further emasculated to 255HP with the same 9.0:1 CR. That drop was "SAE NET".

My 1966 GTO 389ci Tri-Power was rated at 360HP (gross). With a wide-ratio 4-speed manual and 3.55 gears, it was basically a 14.5-second car. My Formula, at maybe 150# less, and 275HP (net) was a 14.2-second car.

[MN6WS6]

Well when Ford made that boo-boo with the Cobra engines is 99 or 00, they must have done the "no accessories, 0% humidity, 0 degree air temperature, and a 100 shot of nitrous" test

[markd79ta]

I've heard that the 79 Trans Am with the 6.6 liter V8 had around 300 horsepower but everything else i checked said it only has about 220 horsepower. Is their any truth to these rumors? I can't imagine a 6.6 only putting out 220 horses although i'd imagine it's possible due to the fuel crisis and emissions equipment choking it.

I think some of the big guns were down rated in terms of HP for insurance reasons. For instance...the L71 and L88... The L71 Corvette were recorded running mid to high 12s on stock bias tires which means that it's 425hp rating was pretty trumped up. The ZL1s were definitely down-graded. Various accounts put that engine in the 500-600hp camp. I also doubt that the '70 & '71 Hemi Cuda power rating is accurate.

The '79 T/A only put out 220hp on the books, but it put out approx 320lbs of torque very low in the RPM range with one flat torque curve. It was a monster for its day considering the 130-150hp V8s. The rating on this car is with a pretty restrictive snorkel system, small y-pipe, one pellet converter, and duals from there. It was choked up pretty good. My car had duals put on it at the dealership where the original owner ordered it from so I have two of the old pellet style converters. I want to put my long tubes on it along with 2 1/2 inch duals and run it at bandimere to see how it does which would give me a pretty good idea of what these cars were capable of from the factory. My engine is completely original except for the battery, water pump, belts, starter solenoid, air cleaner, fuel filter, plugs, and wires. Anyhow, it comes out of the hole a lot harder then my '97 (far more brutal) but chokes up in the higher RPM range. The '77-'79 W72 400 was kinda the last hurrah and the last big block put in a muscle car (well, except the 403 olds put in that model year, but we don't think about that). The compression was bumped up to 8.3ish from 7.7ish (I say ish because all accounts are a little different.) It had a 60psi oil pump. The cam had a pretty high duration but not enough lift. The 6x-4 heads flowed really well but had a much larger combustion chamber then the earlier Pontiac heads thus the low compression ratio. Anyhow, it was a beast for its time in comparison to anything else being put on the road.

I am extremely curious how my R/A III 400 will perform at the dyno...I need to get that project started.

[N20LT4Bird]

I am extremely curious how my R/A III 400 will perform at the dyno...I need to get that project started.

The power band will be similiar. The Pontiac motors run hard out of the hole and then start sucking wind up top. Thats just a Pontiac motor thing. They have lots of low end and mid range torque, which is what you want for a street car - it makes it "feel" fast.

[markd79ta]

The power band will be similiar. The Pontiac motors run hard out of the hole and then start sucking wind up top. Thats just a Pontiac motor thing. They have lots of low end and mid range torque, which is what you want for a street car - it makes it "feel" fast.

Sorry for hijacking this thread. N20LT4Bird, Have you done much with these in terms of lifter/cam swaps? I am trying to figure out what I want to do. In the past few years I have met two guys at SCCA events with 455 HOs that were absolutely amazing. One of them sounded like all heck was going to break lose when he cracked the throttle and made his run. He claimed that it dyno'd well over 500hp at Denver's 5,000+ ft, and I believe him. I asked him what he did..."solid lifters and wicked cam." He had a bunch of goodies like a relocation kit for the oil filters, pressurized system, baffled oil pan, etc. etc. The car was a full-on road racer...cage, lightweight spendy wheels, etc. etc. Both of these cars were pretty incredible though, and I would love to have either. Anyhow, the beast of these two cars had little problem with mid to high RPM HP. I have seen several solid lifter roller assemblies for Pontiac big blocks so I am trying to figure out which way to go; or if they are more trouble then they are worth. My R/A III is rebuilt back to stock, never fired, so I have to make a decision on whether to crack it open again.

[94 formula]

N20LT4Bird your completly right about how the engines make better low and midrange power so they feel faster. GM actually used to refer to it as the grand illusion. They made there motors with more torque so it feels like it has more hp on the seat of the pants test lol. Its also the reason that many people say a stock lt1 feels like it has more power than a ls1 the lt1 has a better low end and feels like its more powerful but run a stock lt1 vs a stock ls1 and see what happens when the ls1 starts pulling on the top end.

[Detroit_Bird]

I think the old cars felt faster due to the "rattle trap effect" also. When there's no sound deadeners, loud exhaust, upright seating position, and little NVH related stuff, cars seem more brutal also. Not to mention the loose, primitive suspensions most had. Don't get me wrong, I grew up on old school muscle, and love to drive and wrench on 'em, but I think this is part of why old cars feel faster than they should.