Engine power Deville 1971 v. 1972

[Soren Johnson]

What happened with the engine in 1972 compared to 1971?
Lower horsepower and subst. lower torque in 1972.
If I have understand it right, the torque in 1972 is about 30% lower than 1971.
Why and how did they do that?
Is it possible to modify the 1972 engine to get back the lost power?

[Philippe M. Ruel]

Part of power loss between 1970 and 1975 is due to emission control regulations, resulting in lower compression ratios on most US engines.
Adding to this, a change in standards occured in 1972 from "SAE gross" to "SAE net" power measurement figures.
SAE gross horsepower and torque are measured on engine crankshaft with no accessories installed like transmission, power steering pump, alternator or water pump.
SAE net measures include all these accessories, they reflect better the real power of a given powerplant on a car. They are usually about 20% lower than SAE gross figures, although no precise and universal conversion can be done.

To get back your engine power, just express it in SAE gross figures  .
Engine modification may always be done, higher compression ratio through piston change / camshaft change / intake and exhaust change / everything they do to bring a car on a dragstrip, you know. Don't expect then any low end torque or smoothness from your Cadillac, but it sure will have power.

[TJ Hopland]

The 68-70's were high compression.  Starting in 71 all GM's were low comp.  The basic engine was the same till 68-74 they just changed the pistons (large dish) to drop the compression.   75&76 had different heads (larger chambers) & more typical pistons, also they dropped the 472.  Only other siginifigant hard part change to the motors were cams, the rest was all in the tuning.

[68 Deville]

 This is the way I understand it  The Horsepower rating System was changed from gross to net in 1972. This is the reason for the charts lower power Ratings. The Only real loss of power came from the lowering of compression in 1970. Even that wasn't much the 500s compression for example was lowered from 10.0:1 to 8.5:1 The result was a loss about 35 hp and 15 ft pounds of torque.