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The Edelbrock heads may increase your CR by about 1/2 a point. Not a problem since the more efficient chambers will have actual quench. The 1969 Six Pack/6 Barrel had an advertised ratio of 10.5 right? Most people feel that the CR was actually less when you calculate the specs. I have a 440 short block and the pistons sit .017 in the hole with double valve reliefs. A 906 head with 88-90 cc chambers, a .020 steel head gasket and pistons ( with 12ccs of valve reliefs) sitting .017 in the hole puts actual compression in the low 9.2 range anyway.



The 69 1/2 engine was actually listed at 10.2,the 70 at 10.5