Source heads, with slight variations, give or take, are 84-86cc. The piston above is a -17cc dish, at .015 in the hole and a .039 gasket I'll get around 10.0cr. with the same chamber, .010 in the hole, .039 gasket, running a flattop I'll get around 11.2cr. a couple years ago, even with alum. heads 11.2cr was to much compression on pump gas, even with a good tune/setup. within the last 1.5 years or so every gas station around here is pretty much E85, where 10.5cr was the high end then, my machinest says now that 11.0cr is becoming the norm due to this gas. I can up the gasket thickness if needed to drop the CR. where I was getting lost, and you answered, was what piston top design would be the best? a full dish has no quench and a pop up would interfere with flame propagation. the piston above has a quench pad, valve reliefs, a reasonable CR and would aid in flame propagation.

Thanks by the way for taking the time to answer my questions!