1973 Pontiac Firebird Trans Am SD-455

A Super Duty (SD) 455 was the beating heart of the 1973 Firebird, and while that wasn’t a new engine, per se, it had a litany of modifications to help bolster performance. These included a strengthened cylinder block, with four-bolt main bearings to help rigidity.

This model variant soon became known as the fastest Pontiac ever. Stock, the engine produced more than 400 hp, but with a race tune (including a modified intake manifold, a more aggressive camshaft, and better headers) that SD-455 could create more than 600 hp and 600 ft lbs of torque.