Another oddity : The 1973 SD-455 GTO was that the SD-455 engine was scheduled for the Lemans, GTO, and Grand Am ONLY, not available in any other Pontiac. Pontiac sent a 73 SD-455 GTO to CARS Magazine, they proclaimed it "Performance Car Of The Year", but by the time the issue hit the newsstands, Pontiac had already notified their dealers that the SD-455 would not be available in ANY A-body, and all of the engines were going into the F-body Formulas and Trans Am's (Pontiac also canceled the availability of the 1973 GTO/Grand Am Ram Air setup, a system that supposed to be exclusive to the SD-455 engine. A few SD-455 A-Body Ram Air setups were later thrown into the parts bins, and about a dozen were sold).
By the way, people always ask about the difference between the 1973 and 1974 SD-455's, as the 1973 was rated at 310 hp, the 1974 was rated at 290 hp. In reality, they were all 290 hp, but press releases and promotional material had already been released with the 310 hp rating from when the car was supposed to receive the RAIV cam. The 1973 and 1974 engines are identical.
Pontiac Engineers produced over 500hp on the dyno using headers and a RAIV valvetrain setup, and the production engine produced around 350 NET hp, and over 400 NET hp once the exhaust was removed, which places this engine on the same level as the greatest powerplants of the 1962-1970 era. Amazing considering the lousy EGR steel intake manifold, pathetic 8:1 compression, and .408 lift cam.
