Quote from: metroplex on December 22, 2016, 04:37:51 AM
QuoteYou don't need a catch can for the clean side. The clean side is primarily a fresh air intake for crank case ventilation. Even on the RX can, the clean side is routed to the filtered side of the airbox (to keep a closed loop system) or to atmosphere (zero vacuum).
The CSS (clean side separator) is just to keep the oil from migrating down your plumbing for the occasional "burps". Primary direction of flow on the clean side is IN to the valve cover.
That's true in theory, just like the PCV valve is a one-way valve so you don't really need an oil separator. But reality seems to be the PCV system allows a lot of oil/vapors to enter the intake manifold, and the cleanside crankcase ventilation does allow fresh air to enter the crankcase, but it can also send a lot of oil vapors into the air tract as shown by ZSHO's photos, and the fact when you look in your air intake tract and intercooler, it is an oily mess.
You are absolutely right. It's hard to tell in ZSHO's photos exactly where the CSS routing is terminating, but the RX instructions say to install a hose barb in the air box lid (filtered side) for the CSS. In theory, this has low vacuum and shouldn't draw much vapor under boost. As you pointed out, theory can be different from reality. I can't remember who now, but someone in JimiJak's XSport write up mentioned they saw some oil seeping into the air box as well when plumbed per RX instructions. This was resolved with a check valve and rerouting the hose, but I'm not sure if this held up long term.
Personally, I resolved this by venting the CSS to atmosphere and removed it from the intake a circuit completely. However, WI is a non-inspection (OBD2 only) state so this was an acceptable solution to me which may not work for others.
Blow off valves are also a source of oil vapors getting back into the intake, and can be resolved by VTA, if you can tolerate the noise.

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