SO I don't post a whole lot over here, but I feel it's time to start contributing and start getting some questions answered for myself and others...

I work in the road racing industry and my company's race car is a 2005 WRX STi. We work a lot with Subarus and the big names in the Subaru performance world.

As I finished everything up on the engine build on my Procharged Trailblazer, I decided that a simple catch can wasn't the best option for relieving PCV system issues that cause our engine to push oil into the intake. I decided to give the Crawford Performance Air-Oil Separator a try. Basically a fancy little unit that uses in an internal centrifuge to separate the oil out and automatically drain it back into the crankcase and feed the clean air back into the engine.

What I need help with is the theory behind how the PCV system in the 2006 LS2 works and how I can make the Crawford AOS function properly. AS the photo I found in the interwebz below shows, the vehicles equipped with a car throttle body are plumbed as described...


The only difference with the truck intake manifolds is that the port labeled in black as "Blank" is fed to the intake and the port in the LS6 valley cover labeled in the photos as "stale air out" is actually capped off.

What I need to know is, can I change the PCV system's direction of ventilation in any way?

The way the crawford AOS works is in the photo below. Basically, the dirty air/oil feeds from the engine to the (2) side ports on the AOS marked with the red arrows. The centrifuged/separated oil returns via gravity and vacuum into the engine from the bottom port on the AOS marked with a black arrow. The clean air after being separated from the oil is returned to the engine through the top port on the AOS marked with the black arrow

 

If your engine is operating normally you will get minimal blow-by in the can - a few tablespoons every few thousand miles. For that reason, most guys dont think its cost effective to plumb the drain back into the oil pan. If you do have enough oil in the can to warrant a drain, then you have a serious engine issue.

 

Okay, let me be clearer...this isn't a stock engine...there are lots of PCV issues with the LS engines as is, and adding lots of boost only amplifies them. Thanks for the response, but your information is false in my circumstances.

 

Ok then let me try to answer your question directly. Changing the direction isnt as easy on the 03+ valve covers beause they switch the vent style from a check-valve style to a fixed orfice (notice the baffeling in the underside of the valve cover). It may be possible, but may not work as well in the oppisite direction. You may have better luck with some 99-02 valve covers. As long as you dont have LS3-based heads they will clear the rockers.

 

Cool! That is what I was assuming and you answered it! Thank you! I figured the valley cover with it's fix orifice would be a bad oil return location, so I may have to find another way to return the separated oil back to the crankcase! Now, both valve covers will work fine as is...I think I am getting a game plan figured out. The only thing I will have to do now is figure out a way to plumb the air return into the intake tract before the throttle body because the increased vacuum during deceleration will cause siphoning of oil right into the intake, correct?

 

Not if your catch can is well constructed. The oil should be well seperate by the time it reaches the exit port. But an easy way to do it would be to put a npt hose barb in before the tb. You could drill and tap the front of the pan for an oil return, similar to how you would do a turbo drain return.

 

It seems like you would need quite a bit of airflow through that unit to get any significant centrifugal action.
I wish I could figure out how to make a mechanical centrifugal separator small enough to fit. The ones that I've seen are the size of a 30 gallon drum, and they have a big, like 1-1/2 HP, electric motor.

 

Any idea what that catch can looks like inside?

PS you've got 2 different heads on that engine

 

Am I the only one wondering about the L92 and cathedral port head on same motor....

 

Yes...probably just for mock up, and its not his.