The 70 455HO is a unique creature as the compression was around 10-1/2 to 1. In 1971 the 455 (and everything else in Pontiac land) dropped to around 8-1/2 to 1. So It is a unique engine given it's one-year availability. As you may know, with Pontiacs, the compression ratio is created by the cylinder heads not the pistons. Most of them use the same type of flat top piston with valve reliefs. No domes here. So this engine will have a rather rare set of heads on it with small volume chambers.
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