I have a Cat SDP that keeps blowing head gaskets. VVAs are off so the stock high compression pistons are too much. Does anybody know what the Cat part numbers are for the correct low compression pistons? Should I be looking for 15.2:1 or 16:1? I've been told I have 18:1 Pistons now. Serial #SDP04546. All liner protrusions are close to .0045. I'm considering counter boring and shimming to .005. Appreciate any help.