The PCV system is for emissions, it recaptures combustion byproducts from the crankcase, and ideally routes them back into the intake to be burned off and run through the catalytic convertor. You want it routed back into the intake after the MAF, but before the turbocharger. That's because everything in the crankcase has already been metered by the MAF and running it through the MAF again can soil the MAF and cause BLM issues. Dumping it to atmosphere also can cause BLM issues, and it smells bad. And it's really bad for the air. Crankcase emissions cause almost as much pollution as the tailpipe.
Plus pulling a vacuum in the crankcase gets air out from under the pistons, which frees up a little bit of power and helps the rings seal better.
I finally got my setup working properly with two catch cans. I ran two PCV circuits. One using the normal PCV port under the plenum, through a high-end check valve to a catch can, and then back into the intake at the plenum. I used a check valve because the OE PCV will leak under higher-than-stock boost and pressurize your crankcase, which makes a huge mess.
The second circuit runs from the valve covers to another catch can, then into the intake pipe between the MAF and the turbo.
In normal operation (vacuum), the check valve on the original circuit is open, and fresh metered air is drawn into the valve covers, through the PCV opening in the lifter valley, through the catch can, and into the intake to be burned. When the boost comes on the check valve closes and the flow reverses. The turbocharger pulls the gasses out of the valve covers, through the second catch can, and into the intake tract.
My system has been working quite well. The car doesn't leak oil anymore, even under extended runs at high boost. I used to get a lot of water/oil mix in the original circuit catch can, but once I switched to a push-loc vacuum setup that all disappeared. I'm guessing the old stuff was leaking so bad it was letting a lot more water into the crankcase. My idle really stabilized when I switched to the new vacuum lines, so it was leaking. I just get a little bit of sludge and sometimes a little water if it's a really humid day. I don't get anything in the valve cover catch can except an oily coating on the inside, nothing collects in the bottom. The breathers I'm using have oil separators in them, so most of the oil is draining back into the valve covers and not making it to the can. I may eliminate the second can.
