Update. For all of you that said bore seal, you were right. Valve guide issues as well.
I spent a day in Greenville TN With Bob at Performance Automotive.
He did a lot of work on Allan Johnson’s Pro Stock project. The first thing he did was run a bore gauge in the cylinders. The block was bored and finished honed when I delivered it to the first shop. I have the receipts from Diamond Racing. The pistons (Diamond) were 8032 alloy, fit at .003-.0035.
So why was there an obvious cross hatch and a measurement of .007-.0075? The first shop obviously didn’t think there was enough clearance?
The intake guides were round, no taper and measured .0015-.0017. But the exhaust were round and straight but .006-.0065?
So, DOUBLE the ideal clearance on the pistons, causing ring failure. The extra clearance in the guides didn’t help either.