It's only had .002" milled just to make sure it's clean and flat. Chamber size is very close to stock at 58cc. The chamber was cast to be the same size as the open chamber. Dutra says they were going to experiment on the quench for fuel mileage, but I have no idea how they were going to do it. Most all the slant sixes I have seen have the pistons down in the hole about .180". Ain't gettin no quench with that. These pistons are .007" in the hole at TDC. The compressed thickness of these steel gaskets is .020", so my quench distance is tight. I have the good ARP rod bolts so I'm not looking for bolt stretch. It was either go about .027" quench distance, OR use a .045" compressed thickness gasket for .052". So I went tight. I don't plan on much past 5500 so we'll see. I ain't skeered. lol