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Well .067 if decks are full spec. still deck it down .027 and with the 413 closed chamber heads milled a bit to make up for the fel pro gasket not hard to get it to 10 to 1 or more.

Easy 9.6 to 1.

Think the original 413 are .082 down!



Well, I agree, although those numbers are a lot more difficult if you're running open chamber heads - say, if you swapped the poor-flowing 516 heads for later factory iron heads.

I'd also wonder if you'd get in trouble not having valve reliefs in the pistons if you start cutting on both the block and the heads.

I've posted recently that with a .050 cut on my Edelbrock heads, my 413's CR will be about 9.6 to one with pistons .080 in the hole. For a street car, that will be good enough - and a lot better than the 8.5 to one it has now with 906 heads even with steel shim head gaskets. If I absolutely had to have more than the milled Eddy heads will give me, or if I was starting from scratch instead of from a running engine, I'd just switch to a 440 block and use off the shelf pistons to build a zero-deck closed-chamber quench motor.