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I had my head milled, more than normal (.060) because I wanted to do some chamber work. I marked the gasket edge on the head and ground the area near the exhaust valves back closer to the gasket edge to unshroud the valves and did a little smoothing. Checked the resulting size and arrived at 70cc. I measured the head gasket that will be used and estimated (guessed) its' compressed thickness at .040 so it should add 8cc or so. Compression ratio = (cylinder displacement+chamber volume+head gasket volume) / (Chamber volume+head gasket volume) My numbers, all in cc's , (628+70+8) / (70+8 That puts me at 9.05:1. Close to maximum I think for a flathead. Probably be a premium fuel burner. Now the questions. How do those numbers compare to any measurements you folks have taken? Does the calculation above make sense to the collective wisdom here? There is a more smoothing that could be done to gain a few cc's if needed. edit to add: This is a 56 Plymouth 230 head. These were advertised originally at 8 or 8.1:1. With the .060 I removed they must have been way under the spec'ed ratio from the factory as the amount removed in the chamber work was not all that much.
