You will always have some pressure leaking past the rings in to the crankcase. Especially so with boost. You just have to make sure it can get out. Get rid of the pcv valve and put breathers in both valve covers. Making a pcv valve work with boost is not an easy task. All kinds of check valves and gizmos are required to separate vacuum and boost and standard pcv valves can’t do it. Btw just because you have 10:1 pistons does not mean you have 10:1 compression. There are way too many factors at play besides pistons. He could have used 10:1 pistons with a big chamber and thick gaskets and got you down to 9:1. Or even 8:1. It’s all in the combo of parts.
