The Ford OEM PCV valve needs to be modified to handle the boost in the intake tract. The solution is a better one way valve. I use a Mazda brake booster valve. It does not let any air escape in one direction. It is made of brass and is very sturdy. I tested it to 60 PSI and saw no leakage. Get a used or new Mazda valve and install it inline with the PCV valve. You should be able to blow through the valve in one direction but not in the other. Install it so that it doesn't stop air from going into the intake manifold but does stop air from going into the crankcase.