92 Sunbird LE
Well-known member
1973 SD-455 engine. The original design of the SD-455 called for a forged crank, Edelbrock P4B aluminum intake, RAIV-spec cam, and a Holley carb. There were several compromises due to cost cutting, plus additional problems getting the engine EPA certified. During development, the use of an Edelbrock intake was abandoned. Engineers then wanted to use a factory aluminum RAIV manifold, but unfortunately the factory intake did not have a provision for the Holley square bore bolt pattern. As a cost cutting measure, a steel 4bbl intake was used. Because of the intake manifold compromise, the use of a square bore Holley carb was impossible, so the engineers resorted to the trusty ol' Quadrajet, but not just any Q-Jet, they had a special unit developed by Rochester to increase flow. The use of a forged crank also fell to cost cuts and was substituted with a cast-nodular crank. The RAIV-spec camshaft (308/320 duration) was also discarded, despite the fact that the SD-455 would have passed its EPA emissions test with this cam, it was determined it didn't pass with enough of a "buffer", so a milder cam (301/313 duration) was used.
Before all this occurred, back in October 1971 Pontiac engineers ran a series of dynamometer tests on the SD-455. In standard form they achieved 404 hp. There was a 20 hp dropoff when a Firebird exhaust system was attached, then another slight drop off when a milder cam was used. When headers were added, horsepower jumped to 451 hp. The addition of a Holley 850 carb added another 12 hp, and finally, a bump in compression up to 11.9:1 produced an impressive 530 hp.
When introduced in May 1973, all the compromises and cost cuts were in place. The factory rated the engine at 290 net hp (early data shows 310 hp, but that version was never sold to the public). With 8.4:1 compression, steel intake, Quadrajet carb, and mild 301/313 camshaft, the 1973-1974 SD-455 was the best engine of the era and easily propelled 3800 lb+ Trans Ams and Formulas to low 14-second elapsed times or high 13's with some traction.
Before all this occurred, back in October 1971 Pontiac engineers ran a series of dynamometer tests on the SD-455. In standard form they achieved 404 hp. There was a 20 hp dropoff when a Firebird exhaust system was attached, then another slight drop off when a milder cam was used. When headers were added, horsepower jumped to 451 hp. The addition of a Holley 850 carb added another 12 hp, and finally, a bump in compression up to 11.9:1 produced an impressive 530 hp.
When introduced in May 1973, all the compromises and cost cuts were in place. The factory rated the engine at 290 net hp (early data shows 310 hp, but that version was never sold to the public). With 8.4:1 compression, steel intake, Quadrajet carb, and mild 301/313 camshaft, the 1973-1974 SD-455 was the best engine of the era and easily propelled 3800 lb+ Trans Ams and Formulas to low 14-second elapsed times or high 13's with some traction.