Crank case pressure or blow by can not be contained, and if you have blow by, it will blast through the path of least resistance.
However you can control where it blasts through and that's where breathers / vents come in, normally located in the valve covers. If it can't escape through vents it will push past seals and or gaskets. Blow by entering the engine air intake through the PCV system is very bad for a performance engine as it dilutes the fuels octane and can lead to detonation or pinging. So the first thing to do is get as much venting as possible. A small vent hole has a "venturi" effect and will pull oil along with it so you need to try and come up with a larger vent than you have. Often engines have a vent breather with a hose nipple that you can attach something like a heater hose to and direct where the blow by goes, usually under the car so you can determine just how much blow by you are dealing with. Sometimes you see a "pan evac system" where the valve cover vent hose attaches to an anti reversion fitting on the header collector to help "evacuate" the blow by from the crank case. The exhaust can actually put vacuum in the crank case, pulling the blow by out. Sometimes vent hoses go to "catch cans" but they also need to be vented.

Thanks
Randy.

-- Edited by GLHS60 on Friday 2nd of May 2014 02:54:09 PM