The Superduty (SD) engine was only available in the years of 1973 and 74. Here's the short history on it:
"The first was the introduction of a new Super Duty 455 V8 (SD-455). "Super Duty" was the name Pontiac used on its high performance (i.e. race ready) engines in the early 1960's, and the Super Duty 455 was a street legal race prepped engine. All SD-455's were hand assembled, and had a reinforced block, special cam shaft, aluminum pistons, oversize valves and header-like exhaust manifolds. Pontiac rated the SD-455 engines at a stout 310 bhp and 390 lb-ft, but experts agreed that it was closer to 370 bhp. This level of engine ratings were unheard of in an era when other manufacturer's engines' output were falling dramatically, and the Firebird became the only true performance car remaining in the market. Unfortunately, Super Duty engines were expensive and therefore rare; only 252 Trans Am's and 43 Formula 455's received the SD-455 engine."
"The first was the introduction of a new Super Duty 455 V8 (SD-455). "Super Duty" was the name Pontiac used on its high performance (i.e. race ready) engines in the early 1960's, and the Super Duty 455 was a street legal race prepped engine. All SD-455's were hand assembled, and had a reinforced block, special cam shaft, aluminum pistons, oversize valves and header-like exhaust manifolds. Pontiac rated the SD-455 engines at a stout 310 bhp and 390 lb-ft, but experts agreed that it was closer to 370 bhp. This level of engine ratings were unheard of in an era when other manufacturer's engines' output were falling dramatically, and the Firebird became the only true performance car remaining in the market. Unfortunately, Super Duty engines were expensive and therefore rare; only 252 Trans Am's and 43 Formula 455's received the SD-455 engine."
