Horsepower Comparisons
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From: Forney Texas
Horsepower Comparisons
I was looking through my October/2005 copy of Corvette Fever and it had an article listing the top 15 small block engines installed in Corvettes. My question concerns the stated the horsepower rating of engines from the sixties/early seventies vs ratings from the nineties to today. I noticed L84 from 1965 shows to be a 327 ci 375hp/350tq. The LT1 from 1970 is a 350 ci 370hp/380tq. In looking at the rating for my 1990 L98 and it is 245hp/345tq while the 1996 LT4 was rated at 330hp/340tq.
I have seen 1/4 mile times from some of the older cars and if my memory is correct the older cars were slower than newer cars with a lower power rating. Did the rating system change? If it did how did it change and using the old system how would the LT4 for instance be rated?
Just curious.
90Indy
I have seen 1/4 mile times from some of the older cars and if my memory is correct the older cars were slower than newer cars with a lower power rating. Did the rating system change? If it did how did it change and using the old system how would the LT4 for instance be rated?
Just curious.
90Indy
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by tnt-sportfishing
The newer vettes are rated at rear wheel hp, (rwhp). Older cars had just engine hp ratings. Your engine hp is much higher than at the rear wheel.
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by tnt-sportfishing
Well my 92 is rated at RWHP and all articles I'm reading as well as owner video's from Bollingreen, states RWHP. I just read in a Mag the same statment I stated above.
Team Owner
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From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
tnt, take it for what it's worth: there WAS a change from Gross HP numbers to Net HP numbers, which accounts for the difference in numbers AND performance figures. Kid from NC is right. And whatever hp number you've got, there is nothing in the literature that is a rear wheel horsepower number ever put out as a promo or spec in an owner's manual by GM.
Instructor
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From: So. Jersey
I agree about the change, in gross to net. It will drive me crazy to find the info on the rwhp. My dyno from the factory has my vehicle with 300 hp and 340lbs of torque up 10lbs from the 330 predicted. Maybe i missed read somthing but I just read the articles on rwhp compared to early days of gross hp. I'll probably find it when i'm not looking for it. couple hundred mags to look through 
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Melting Slicks
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From: Hewitt NJ
Originally Posted by tnt-sportfishing
Here's a question If my vehicle has 340lbs of torque at the wheels, does the dyno read the hp at the wheels or net hp at the crank?
GM went to net HP ratings in '72. That is one of the reasons there was such a huge difference in HP ratings between '71 and '72.
FWIW our 92-96 LT1s would probably be rated around the 370-380 gross HP mark.
Le Mans Master
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From: Clearwater FL
St. Jude Donor '06
Our cars are not rated rwhp from the factory, they are crank hp. Most LT1's dyno around 270 and LT4's around 300 rwhp stock. Add aprox 15-20% for drivetrain loss to get the chp figure in net hp.
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by tnt-sportfishing
Here's a question If my vehicle has 340lbs of torque at the wheels, does the dyno read the hp at the wheels or net hp at the crank?
Instructor
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From: So. Jersey
Originally Posted by Admiral94
Sounds like your taking the figures that are stated on the tag attached to your console. Those are flywheel HP not RWHP.
GM went to net HP ratings in '72. That is one of the reasons there was such a huge difference in HP ratings between '71 and '72.
FWIW our 92-96 LT1s would probably be rated around the 370-380 gross HP mark.
GM went to net HP ratings in '72. That is one of the reasons there was such a huge difference in HP ratings between '71 and '72.
FWIW our 92-96 LT1s would probably be rated around the 370-380 gross HP mark.
Team Owner
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From: Athens AL
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GM switched from gross to net in 72.
Net HP is measured on an engine dyno with all accessories on the engine, AC, alternator, PS, everything on the running motor.
Gross is done without all that.
A general rule is that you can add 20% to a net rating to get the equivalent gross rating that it wouldve had in the pre-emissions days.
Chassis dyno's, which is what we all use outside of a builder's shop, measure the power put to the rear wheels, and the difference is lost to the driveline--mostly the transmission itself. You'll lose typically 15-20% from the net rating.
Net HP is measured on an engine dyno with all accessories on the engine, AC, alternator, PS, everything on the running motor.
Gross is done without all that.
A general rule is that you can add 20% to a net rating to get the equivalent gross rating that it wouldve had in the pre-emissions days.
Chassis dyno's, which is what we all use outside of a builder's shop, measure the power put to the rear wheels, and the difference is lost to the driveline--mostly the transmission itself. You'll lose typically 15-20% from the net rating.
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From: Athens AL
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Originally Posted by tnt-sportfishing
Gotcha, thats some of the info i was reading, so what is rwhp with these ratings, and why did the switch from gross to net? where is gross taken from?
Race Director
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From: Slidell Louisiana
Originally Posted by Corvette Kid NC
No, the newer cars for quite some time now have been rated by net HP while in the old days it was gross HP. Also, most of the 1/4 times you'll see for the old ones would have been achieved with the wholly inadequate OEM tires of the time.
Chris is correct on this! That is why the 300 net HP gen II SBC was called LT1 since it had about the same output as the legendary LT 1 which was rated at 360-370 HP .
The 1971 LT-1 had its compression dropped and was rated at 330 horsepower gross and 275 horsepower net.
Mike
Mike
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From: Prattville, AL. My Dog Thinks I'm Cool!
Originally Posted by Admiral94
FWIW our 92-96 LT1s would probably be rated around the 370-380 gross HP mark.
I read in some mag that at the time of it's introduction the LT1 was the most powerful pushrod small block that GM had ever produced. 
Last edited by pletner; Dec 5, 2005 at 06:43 AM. Reason: Left out the word pushrod. Don't want the ZR-1 owners hating me!
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Originally Posted by tnt-sportfishing
The newer vettes are rated at rear wheel hp, (rwhp). Older cars had just engine hp ratings. Your engine hp is much higher than at the rear wheel.
Originally Posted by Eddie's 84 vette
