The engine I'm running right now has 346 open chambered heads they were cc'd at 88cc's, flat tops .070 in the bore, with .020 compressed head gaskets. According to Summit's calculator, I'm at 9:23 compression. I was asking about using the closed chamber heads because I have a set of 516's that have been mildly ported, with the exhaust valves opened up to 1.74. My original post was that I wanted to build another engine with zero deck flat tops using the 516's that I already have. The engine I'm currently running originally came with 915's, but they are long gone. If the 516's are really 84 cc's, perhaps I could use them on the engine I have to pick up some compression without going overboard. I am just trying to get some input from experienced engine builders. At some point in the not to distant future, I want to build another engine. Will zero deck flat top pistons work with aluminum heads? I am under the impression that aluminum transfers heat and you can run higher ratios without detonation. Am I wrong on this assumption?