73 VETTE

[JAMES RICHARDSON]

IS THE MOTOR CONFIG (454) IN A 72 THE SAME AS THE 73 (454)

I HEARD THAT GM CHANGED THE RATING SYSTEM FOR HP/TORQ IN 73 BUT THE MOTOR IS THE SAME SPEC AS A 72 (454)

[Joe L.]

Re: 73 VETTE

James----

The horsepower rating system for Corvettes, and all U.S. manufactured cars for that matter, changed BEGINNING in 1972. Prior to 1972, vehicle engines were rated on an SAE-gross basis. From 1972 forward, vehicle horsepower was rated on an SAE-net basis. SAE-net is a system in which the engine is rated on an AS-INSTALLED basis, with engine accessories included. It is NOT, however, a rear wheel horsepower rating as some folks believe.

With respect to 1973 vs. 1974 engines, both LS-4 engines are BASICALLY the same. Although they use different cylinder heads and intake maifolds, the configuration of those components is very similar. The biggest difference between the engines is related to emission control equipment. The early 70s was a period of rapidly evolving emission control requirements, leading up to the initial use of catalytic converters on Corvettes in 1975.

So, the bottom line is, the 73 and 74 engines were very similar, but not identical, in basic core engine configuration, but were different in terms of peripheral equipment.

[Joe L.]

Re: 73 VETTE

James----

The horsepower rating system for Corvettes, and all U.S. manufactured cars for that matter, changed BEGINNING in 1972. Prior to 1972, vehicle engines were rated on an SAE-gross basis. From 1972 forward, vehicle horsepower was rated on an SAE-net basis. SAE-net is a system in which the engine is rated on an AS-INSTALLED basis, with engine accessories included. It is NOT, however, a rear wheel horsepower rating as some folks believe.

With respect to 1973 vs. 1974 engines, both LS-4 engines are BASICALLY the same. Although they use different cylinder heads and intake maifolds, the configuration of those components is very similar. The biggest difference between the engines is related to emission control equipment. The early 70s was a period of rapidly evolving emission control requirements, leading up to the initial use of catalytic converters on Corvettes in 1975.

So, the bottom line is, the 73 and 74 engines were very similar, but not identical, in basic core engine configuration, but were different in terms of peripheral equipment.

[Jack H.]

Re: 73 VETTE

Adding on, I believe the '72 AIM also provides a 'conversion' chart (maybe CSM too) showing SAE Net/SAE Gross ratings. Interesting, memory says there was a resonable disparity of 'deltas' (difference between net and gross) across the Chevy line indicating power transfer efficiency varied with power plant application....

[Jack H.]

Re: 73 VETTE

Adding on, I believe the '72 AIM also provides a 'conversion' chart (maybe CSM too) showing SAE Net/SAE Gross ratings. Interesting, memory says there was a resonable disparity of 'deltas' (difference between net and gross) across the Chevy line indicating power transfer efficiency varied with power plant application....