My 512 / 518 C.i. street motor had low tension oil rings when I first put it together, it was a bear on crankcase pressure, epscially above 6000 RPM I ended up replacing those rings with the a set of file to fit moly rings with standard tension oil rings and it got a lot better Adding the second breather cap and the other PCV valve helped also BYW, going to the standard tension oil rings did NOT hurt the power, ET or MPH, if anything it helped all three by having less oil in the combustion chambers when revved up above 5000 RPM