Air Oil separator

[tmoretta]

Anybody recommend the best air oil separator for the 818 with EJ20 turbo? There are so many choices of design: some simple, some with more ports and inlets, some that are coolant water heated, some mount on the oil filler and others dump oil back into the oil pan. Very confusing choice.

[Hindsight]

The only one that has been tried and true, race proven and race tested for many years is the one from Crawford Performance. That said, there are others and some may work great and some may not. If you buy one, make sure to mount it high up where the return line out the bottom has a continuously downward slope and doesn't at any point go back upward which will trap oil. I mounted mine to the upper frame and it sits up inside the engine cover jump.

[tmoretta]

Now the Crawford is offered for either TMIC or FMIC. Mine is '02 subie on which I am retrofitting an AWIC. More confusion.

[Sgt.Gator]

I spent a lot of time reading up on aos's. There is a monster thread on IWSTI or NASIOC that's in the 180 pages now, and I unfortunately read the whole thing a year ago! I'll make a general conclusion from that thread: 1/2 of the forum thinks AOS's a re great. 1/2 thinks their AOS blew up their engine.

The general consensus on the LGT forum, supported by my tuner (Cobb), is that for less than 350 AWHP the stock system is the best. Too many problems have popped up with AOSs to be worth the risk for a moderately powered car. Just keep your factory PVC system in top shape. My 2005 Legacy GT 310 AWHP Factory Supported/Phoenix Racing Built+Raced Grand Am Cup car still had the factory PCV system and worked just fine. When Cobb restored the car in 2011 we kept the factory PCV system, it was discussed going with an AOS but decided against it. I never had problems with excessive oil in the intake.

I bought my Spec B with a Crawford AOS already installed. I prepped the car for a track day at ORP and lasted 20 minutes before spinning a bearing. At least part, if not all, of the blame I lay on the Crawford AOS being improperly installed. It had a kink in the drain back line to the block down in there where you can't see anything without disassembling a lot of parts. That filled the intake and FMIC up with oil.
So it's not the Crawford AOS's fault, but I have a bias now.
IMHO the Perrin is the best design on the market. It could be my bias though. It's definitely worth downloading the installation instructions for both the Crawford and Perrin and deciding for yourself.

So my current conclusion is keep the factory system for street/track cars of moderate power. If you're building a race car go dry sump which eliminates the need for an AOS.

One thing is certain, don't use the Grimmspeed AOS on a track car. It may be fine on a street car. But they are not for high G track cars.

[redfogo]

I went with a dual catch can from saikoumichi great quality part. They also seem to have put a lot of testing into there stuff as well!

http://www.saikoumichi.com/DC3_page.htm

[jcpresto]

I have the IAG, however I'm not sure I have an opinion. It was what my tuner suggested.
http://www.iagperformance.com/mobile/Product.aspx?ProductCode=IAG-ENG-7150

[NevaLift2Shift]

I do have a used Perrin AOS I'm trying to get rid of. I went with a dry sump, so I don't need it anymore.