Question: Actual HP ratings ??

[jims427400]

We've all read about how the L88s were really not 430hp but actually like 560hp. Is there a source that has tells the true story on HP ratings for the us and not the insurance companies.
I'm interested in:
-67 427s
-70,71,72 LT1s
-70,71,72 454s

Thanks,
Jim

 

[JohnZ]

Advertised horsepower ratings through 1970 were derived using the "SAE Gross" method, with the engine set up on a dyno with no accessories, zero-restriction dyno exhaust systems, and carburetor and timing calibrations optimized for each individual dyno run. This resulted in very optimistic numbers, not representative of the "as-installed" in the car condition, and Sales had as much input in the advertised numbers as Engineering.

The "SAE Net" method was adopted beginning in 1971, which had the engine set up on the dyno "as-installed", with accessories, production exhaust system, and the single released carburetor and distributor calibration. This resulted in much more honest numbers, which dropped again in 1972 as compression ratios were further reduced for emissions compliance.

The L-88 was a unique situation; it was designed from the beginning as a race engine, to be run with full headers and open exhaust on race gas, not on the street with stock exhaust and premium fuel; bolting on the properly-designed factory over-the-counter open headers and re-curving the distributor for race gas was good for a gain of well over 100 horsepower from the stock as-installed configuration.

 

[Hib Halverson]

We've all read about how the L88s were really not 430hp but actually like 560hp. Is there a source that has tells the true story on HP ratings for the us and not the insurance companies.
I'm interested in:
-67 427s
-70,71,72 LT1s
-70,71,72 454s

Thanks,
Jim

560hp@6800 rpm is generally accepted as the true power output. Back then, the power figures were taken from an engine having not accessories, fitted with open headers, tuned for optimal fuel and spark and running on high-octane leaded gas.

The 430hp rating is actually "legit" but was taken at an rpm way off the engine's power peak. I've never seen a specific rpm published by GM but I have seen anecdotal evidence that it was taken somewhere between 4600 and 5600 rpm.