Horsepower Question?
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Le Mans Master
Joined: Feb 2006
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From: In The Hardwoods Up North
Horsepower Question?
I know GM changed the way they rated hp some time in the early 70s for insurance purposes, my question is what would be the hp rating on a 78 L-82 220 hp if it was calculated the early way? even a guess? thanks ray
Race Director
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From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by 78SA
I know GM changed the way they rated hp some time in the early 70s for insurance purposes, my question is what would be the hp rating on a 78 L-82 220 hp if it was calculated the early way? even a guess? thanks ray
Race Director
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From: Foxfield CO 1970 Convertible
It wasn't for insurance purposes. The industry standardized their measurements and tried to reflect the actual engine output by measuring the power with accessories on the engine.
Safety Car
Joined: Dec 2004
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From: San Diego CA
Gross horsepower was made by an engine with open exhaust and no accessories attached to it, while the engine was on a stand, not in the car.
Hence why they changed to net horsepower which measures the actual horsepower you'd get from it.
Hence why they changed to net horsepower which measures the actual horsepower you'd get from it.
Team Owner
Joined: Oct 2004
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From: Springfield MO
St. Jude Donor '07
Originally Posted by Z-man
It wasn't for insurance purposes. The industry standardized their measurements and tried to reflect the actual engine output by measuring the power with accessories on the engine.
Melting Slicks
Joined: Jan 2004
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From: New Cumberland PA
Originally Posted by Brad Maynard
probably would be 60 or 70 higher, I think
That would be a fair guesstimate. The way they rated the horsepower and the addition of more pollution items lowered the hp rating.
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Team Owner
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From: Huntersville NC
I don't know if all GM models or all U.S. manufacturers changed at the same time, but for corvettes, you will note that up to and including the 1970 model year hp was gross, then in 1971 they did provide both gross and net (although I think still gross was used most frequently) then in 1972 they went to net hp ratings. That is why you see dramatically lower hp ratings from 1970 models to 1972 models with similar engines. There was a drop due to lower compression ratios and perhaps more smog equip (?) but the actual drop in hp is not nearly as huge as what you lost by reporting net hp instead of gross hp.
1970: base = 300hp, L-46 = 350 hp, LT-1 = 370 hp, LS-5 = 390 hp
1972 base = 200 hp,(no L-46) LT-1 = 255 hp, LS-5 = 270 hp
1970: base = 300hp, L-46 = 350 hp, LT-1 = 370 hp, LS-5 = 390 hp
1972 base = 200 hp,(no L-46) LT-1 = 255 hp, LS-5 = 270 hp
Last edited by PRNDL; Feb 16, 2006 at 01:56 PM.
Le Mans Master
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From: Fremont CA
In 1971 GM made all engines able to run unleaded fuel. The compression ratios were dropped and different cylinder heads were put on the LT-1. The 370HP rating of the 1970 LT-1 was actually acheived with the 327-365HP 302-290HP "30-30" camshaft profile. The 1970 LT-1 cam is a little smaller than the 30-30 cam and I really don't think the 70 LT-1 is a true 370HP. The 1971-72 LT-1 motors are essentially the same so the HP dropped from 330HP to 255HP under the new SAE testing standards of 1972. You L-82 would "gross HP" at around 300HP using the old standards.