What makes a 455 super duty different from a 455?

Answer 1

The Pontiac 455 Super Duty was a re-engineered for racing version of the regular 455 Pontiac. It had a stronger block with cross webbing in the lifter valley, malliable iron four bolt mains, provisions for dry sump oiling, forged steel connecting rods, forged aluminum pistons, 80 psi oil pump, Better flowing cylinder heads with pressed in tubes sealing the intake pushrods and round exhaust ports, longer valves (inconel exhaust valves), stronger valve springs, a high flow cast iron intake manifold, high flow cast iron exhaust manifolds (same as ram air iv and 455ho) Other unique feature of 455SD was the small cam gear, larger distributor drive gear, and corresponding larger hole in the block for the distributor. The SD was origanally slated to have the ram air iv 308/320 cam but could not meet emission standards, so the smaller ram air III cam was substituted for production. The 455 SD was underrated @ 290hp, but road tests of 1973-1974 Trans Ams showed quarter mile times in the mid thirteens at 104-107 mph, indicating a true net output of more than 350HP. If it had been born a few years earlier with high compression and the larger ram air iv cam it surely would have had a 425+ gross HP rating.