I'm looking into a catch can for my NA-T build I'm in the process of. I'm wondering why the complexity with all the kits I am seeing. If you look at these kits for the GS/IS/SC they route lines all over across the engine, two cans, etc. I am use to just putting a can in between the pcv and manifold vacuum. Is there something I don't know about that's specific to these engines?

Take this photo for example:


Air is drawn into the the exhaust side valve cover through the line with the blue circle and into the crank case. It is drawn out through the intake side valve cover at the red circle where the pcv valve is by manifold vacuum and sucked into the intake. The system only travels this direction and with the pcv valve being a one way check valve, it stops it from going the other way when manifold vacuum is lost. So why do people run a line from the inlet to a can, then to the engine, then back to a can, then to the intake? And various other methods? With the turbo kit I wont have the line going into the blue circled inlet. But why can't you just put a breather there, and a can between the pcv valve and the intake? Wouldn't this serve the same purpose as the intricate systems being sold? The purpose of a catch can is to stop oil from being drawn into the intake yes? So all that's needed is a can put in line between the pcv vale and the intake vacuum port correct?

 

And before someone makes the comment, I am aware this is not a 2nd gen GS engine. But the system is the same and it was the best picture example I could find of what I'm talking about.

 

Both valve covers output to the catch can. The catch can can either vent to atmosphere, or if it has baffles, be connected to the intake and recirculate the air sans oil particles. Under boost your stock PCV valve will shut (due to the high manifold pressure), which means you will have crankcase pressure venting only through the exhaust side. You can put just a filter and vent this blow-by all over your engine, or you can vent it into a catch can where the oil content will be condensed.