Massive oil leaks.

My dart makes over 800 hp and I use the moroso system that uses the headers to pull pressure from the valve covers. I plumbed the hoses with braided line, like fuel lines so NHRA would not give me crap about rubber hoses. I never liked using just breathers. Like I Mentioned before the Electric vacuum pump from Moroso will solve the pressure issue. It will help the power also. If I had more money for my motor I would run a belt driven pump, they make more power! Ask a race builder the hp gain is worth the power used to run the pump, and no leaks! good luck