I have currently .043 squash area. I have read that .040-.050 is good for cars but I also have a Harley and they run .025-.030 squash, is there a reason why you can't tighten up the squash more on a car engine, I can't believe that an air cooled engine expands less (especially a Harley) than a water cooled engine.
I am using Egge pistons which they claim have a higher silicone content than a standard cast piston (could be BS) but I'd like to take it down to about .025, I find it hard to believe that things expand that much to cause a problem.
Any experts out there that can give an opinion?

 

I am not an expert, but wonder if the piston-to-head clearance has more to do with the piston's ability to rock on the wrist pin than it has to do with thermal expansion. If the piston can rock in the bore at TDC, one side will be higher (and closer) to the head than the center of the piston. In addition to that, at high RPM, inertial forces will tend to "stretch" the rod and allow the piston to come closer to the head.