I've been working on my G for a while and have noticed a decent amount of oil in the plenum (as expected). I have a catch can with a breather, and want to install the full system (by joining passenger and driver side PCV's to the can) then plug the holes on the plenum and intake. So no oil or vapours enter the engine.

Now from what I've researched the crankcase relies on the vacuum caused by the intake system to pull corrosive gasses as well as pressure out. If I install this full catch can setup there will be no vacuum pulling the gasses out, and only pressure from combustion pushing the gasses out (which isn't very strong). My question lies on what this means for the life of the engine? Sure it wont be burning oil anymore, but might I run into other issues down the line?

I know people are running these setups, but I can't find the details.

*Yes I have searched for an answer everywhere*

 

The purpose of an open to atmosphere breather is to lower the crankcase pressure or stop excessive amounts of vapors from entering the intake. It's probably only really a necessity on FI cars as positive manifold pressure blocks off the pcv valve.

I doubt your car has excessive crank case pressure so I would recommend you leave your CCV system closed. Blow-by gasses are the nastiest thing emitted from an engine and you'll quickly learn how they can find there way into the cabin and literally make you sick. Plus, as you stated, the fresh air supply is probably a good thing for a street car that sees light throttle majority of the time.

If you car concerned about oil entering the intake, your best bet is to find an oil separater or "catch can" without a breather.