Quote:
Originally Posted by GR8ONE68
That makes sense, glad my math was correct. I always wondered how a '68 428 GP could have the same CR as a '68 400 GTO with the same 16 heads. Obviously, it can't/doesn't.
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The 428 engines all used a piston with a 12cc dish so they could use the same heads as a 400 and maintain close to the same compression ratio.
Similar deal with 421 and 389 engines. The 421 pistons had very large deep valve reliefs as compared to the shallow small reliefs on 389 pistons. Definitely a big difference in valve relief volume between the 421 and 389 pistons, very likely a 6cc difference between the two.
