Air Oil Separators

[Bob_n_Cincy]

So I have checked with Perrin, Crawford, Element Tuning and ARE and all are in favor of still running a AOS with a dry sump, I know Leo (Green Center drive) has been doing this with good results

Did they say why? What does an AOS + DS do that a DS doesn't already do?

All claimed it reduces sludge build up as therev still will be bypass out of the vents, I would think that this would not apply to folks are running a closed vacuum system. which i'm not

This is strange that they still want an AOS.
The dry sump tank is essentially a large AOS. The swirling air in the top of the dry sump tank separates the oil and air. The oil going to the bottom of the tank and the air going out the top of the tank to the valve cover ports. If there is extra air caused by blow-by, this goes to the small breather tank.

I am not running a vacuum regulator on my system. I deleted my PCV System.
I have no connection from crank case fumes to the intake track, so no oil/sludge can get to the intake track.
Bob

[FFRSpec72]

This is strange that they still want an AOS.
The dry sump tank is essentially a large AOS. The swirling air in the top of the dry sump tank separates the oil and air. The oil going to the bottom of the tank and the air going out the top of the tank to the valve cover ports. If there is extra air caused by blow-by, this goes to the small breather tank.

I am not running a vacuum regulator on my system. I deleted my PCV System.
I have no connection from crank case fumes to the intake track, so no oil/sludge can get to the intake track.
Bob

The point is if you already have an AOS there is no need to remove it, I doubt if I did not have one I would go out and buy one

[Sgt.Gator]

I can think of two reasons to remove the AOS if you have a dry sump:

1) You have to think thru how the gasses will flow with a DS +AOS. Normally a AOS uses Positive crankcase pressure + Inlet vacuum to move gasses out of the crankcase and thru the AOS. And the AOS can be hooked up in several different ways depending on if you keep the PCV. Just look at the Perrin installation document for examples of different setups. With a DS scavenge it's going to work quite differently. Be sure you understand the unintended consequences!

2) An AOS creates several potential points of failure for oil leaks and vacuum leaks. Those leaks could be on the outside of the engine causing a fire, or inside the Inlet coating your TMIC/FMIC/AWIC with oil and causing detonation.

On AOS's in General, the subject of this thread:

As with most mods "it depends". There are endless versions of catch cans and AOS installs. Some are for pure street cars that have a lot of blow by on loosely built forged motors. Some are for track day cars that never go more than 20-25 minutes on a track. And some are for full race car applications. I have my opinions, YMMV, so here's my $.02:

1) Street Car with oem block and typical stage 1-2 build. Stay OEM PCV. It works fine.

2) Track car doing HPDE events of 25 minutes on an OEM block stay oem PCV. Check your inlet tract for excessive oil. (From MAF to Turbo, and in the TMIC or FMIC piping). My Grand Am Cup Subaru still had the factory PCV system and it worked fine. There was a small amount of oil in the intake tract, but not enough to worry about. My tuner, Cobb, recommended staying with the oem PCV during the restoration from 2006 specs to 2011. In their opinion the problems an AOS can cause outweigh the value on a stock block 300 HP engine. I never regretted that decision.
If you have a lot of oil in your intake tract check over your PCV system closely for issues, replace PCV valve, if still a lot of oil go to #3.

3) Track car doing HPDE on built forged block and/or you are having issues with oil in your intake tract, consider an AOS. I've looked closely at all of them. I had the Crawford AOS on my Spec B. Today I would go with the Perrin. KillerB has a new one but I know of no reviews yet. IAG also has a nice looking one: http://www.iagperformance.com/IAG-Co...g-eng-7251.htm

4) Race car, as in dedicated to nothing but racing. Perrin AOS/IAG/KillerB/Crawford or Dry Sump. I personally skip straight to dry sump for all my race cars now, but I recognize that's very expensive.

In 1-3 of the above if you don't have a bunch of oil in your intake tract or tmic/fmic piping stay with oem pcv.

Remember an improperly configured catch can/AOS can be worse than an oem PCV! I think a Crawford AOS that had a pinched block feedback line contributed to my Spec B spun bearing, it at least caused a ton of oil in my intake tract. I mean a ton of oil!

And the consensus from numerous folks is to stay away from the Grimmspeed AOS that goes in your oil fill tube if you are tracking your car. It may be ok on the street, but on a race track it's not.

There's a monster thread about this at IWSTI, 172 pages. I've read the entire thing and came to the following conclusion: 1/2 of thread posters think AOS is great; 1/2 of posters think their AOS destroyed their engine.

http://www.iwsti.com/forums/2-5-lite...ns-thread.html

Great diagrams in the first post.

[SixStar]

The 818R has a Crawford on it that will be replaced with an IAG Race AOS soon.

Never had any issues with the Crawfish TBH.

[STimedic]

My .02 from owning my 05 STi-swapped bugeye, I decided on the Moroso dual-can setup. It was recommended to me by a Subaru master tech buddy who had a hand in designing the setup. Worked flawlessly and keeps both sides of the crankcase ventilation system clean. It will find its way onto my 818C once I get everything together.