X head milled to closed chamber ?

66fs said

Custom pistons would probably be cheaper. 1967 915 heads are closed chamber as are 516's. The 516's in stock form will loose to the better flowing 906's. Search IQ-52's low compression 440 build. If you know the right combination, you can get a lot more than 280 HP, open chambers and all.

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I am aware of that build. And I do have a pair of 516's to work with. They would need porting and larger exhaust valves. I may copy the build. Only thing is I really would like to run stock hp exhaust manifolds and I'm guessing I will loose a significant amount of power. I do have a set of headers I can use if it doesn't satisfy me.