I had issues on my old street pump gas 518 C.I. 400 stroker motor with the original six pack blowing oil out of the breather caps with two caps and one PVC valve when I raced it shifting at or above 7000 RPM, I added another PVC valve with a T to the vacuum side and that stop the problem That also made the motor idle better which allowed me to lean down the idle mixture screws on all three carbs. a tiny bit