Compression ratio might be less than that, I'm not sure. 72cc heads, flat top piston with 6cc valve reliefs, standard stroke + .030 bore. it seems that the pistons were down in the cylinder a bit and not zero deck, probably around 10.5:1.
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1970 Firebird 3200lbs - CVMS built, pump gas 461, 3.89 gear 29.5x10 inch tire,... 10.40 @ 129mph.
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