Air Oil Separators

[DMC7492]

Hi Guys I have been looking at the Perrin AOS. I like the cyclonic action of the air, it makes sense and I don't like the idea of throwing oil mist into the intake of any engine. Does any body have any experience with other brands?http://perrinperformance.com
27085

[Rasmus]

Here's an excellent article I found on the various types of crankcase ventilation systems (http://www.motoiq.com/MagazineArticles/ID/2032/Crankcase-Ventilation-Explained--NA-Edition.aspx). It also explains what crankcase ventilation is and why you need it. The article goes into the pros and cons of each type and even provides an overall recommendation.

Everything from open-to-atmosphere to vent-to-exhaust-via-venturi.

There's six pages. So get to reading/clicking.

[bompus]

I ordered the Perrin AOS a few days ago. Never used an AOS before, but it seems to be better designed than most. An alternative would probably be Crawford, but they borrow innovation from each other as far as I can tell. I've heard from several Subaru owners, tuners, and companies that all say an AOS is almost necessary for track days and highly recommended for daily driving. Everybody has their opinions, but I went with the consensus / my gut feeling on this one and got the Perrin.

[longislandwrx]

Popular opinion is that a catch can is better on a track car than an AOS... the benefit of the AOS is that it is zero maintenance and doesn't need to be emptied, on a track car emptying before/after a race is NBD

Track cars and looser motors with more blowby are also usually too much for an AOS.

AOSes are also not recommended for vehicles typically do short drives and ones don't spend much time at operating temperature as they tend to create the oil/water vapor foam. The Perrin's design reduces (doesn't eliminate) this at the cost of being larger heavier more expensive and requiring coolant lines. It is a very nice unit though.

For this car, I was originally going to go with a GS AOS but I will just save the money and get a std catch can.

[wleehendrick]

For my 818, I think a simple catch can is preferred/sufficient over an AOS. After looking into it, I see there are numerous ways to hook them up. From this thread (http://forums.nasioc.com/forums/showthread.php?t=754710):

How should a catch can be installed?

There are a variety of ways to install a catch can. There's one right way, two sort-of right ways, and some would argue that at least one common installation method which is wrong.

Sort of right ways:
1) Disconnect the hose which runs between the PCV valve and the turbo inlet pipe. Run a line from the PCV to the catch can, and another line from the catch can to the turbo inlet hose.

2) Disconnect the hose running between the crank case breather lines and the turbo inlet pipe. Run new hose between the breather line and the catch can and another hose between the can and the inlet pipe.

Right way:
Use two catch cans. Configure one as discussed in option one and the other as described in option 2. For optimal effectiveness, this is the way to go.

Wrong way:
Disconnect the PCV<->Inlet line as well as the Crank Vent<->Inlet line. "T" the PCV and Crank vent lines together, and run the remaining end of the "T" to a single nipple on the inlet pipe. Cap the remaining nipple on the inlet. You'll be sending boost into places that definitely shouldn't ever see any. Bad idea.

I haven't read through all 12 pages of the thread; what's preferred on the EJ? Are 2 cans necessary?

Thanks,

Lee

[bompus]

Just in case anybody wants more info on AOS ( may also be good info for catch can ), here are downloadable instructions for a couple of AOS systems:

http://www.crawfordperformance.com/wp-content/uploads/2014/02/S0715-1-Air-Oil-Separator-FMIC-02-07-STI-WRX-Install-Version-2.pdf and http://perrinperformance.com/attachment/78718-.pdf

Note that both of these units are designed to run coolant lines to them to heat it up and reduce the amount of sludge. To my knowledge, these are the only two AOS manufacturers who built a heating system into the unit. I've never used either so I don't have a review on how it works, but I'm planning on using the Perrin because they explained how it worked better and you can disassemble it. The Crawford that many swear by cannot be disassembled as far as I know.

[Westview]

If you have some time on your hands, like hours worth, you can read this thread on the topic: The Official STi engine Venting, A/O Separators, and Catch Cans Thread!! (http://www.iwsti.com/forums/2-5-liter-litre-factory-motor/146699-official-sti-engine-venting-o-separators-catch-cans-thread.html)

I use a Crawford AOS on my 2008 STI. There doesn't seem to be a perfect solution.

[Bill Waters]

Rasmus - agree - terrific article; thanks for posting. Who makes an active pump system for the Subies- anyone know?

Thanks,

Bill

[Rasmus]

Rasmus - agree - terrific article; thanks for posting. Who makes an active pump system for the Subies- anyone know?

http://www.moroso.com/eb/web/images/22640_part.jpg
Moroso's Universal Fit.
(http://lmgtfy.com/?q=Moroso+22640)
I haven't seen one. Might be because if you're at the level of HP that needs an active vacuum pump you're making your own brackets.

But using slash cut venturii in the the exhaust, after the catalytic converter, is a great, inexpensive way to generate vacuum. Plus they generate lots of vacuum in boost and at WOT when you need it the most.

[ssssly]

I run the GS AOS with a inline AOS made for air compressors on the line that goes back to the turbo inlet. The GS AOS didn't quite keep up with track conditions. With the GS and the inline, my intake is bone dry even after the hardest driving I've thrown at it.

The Venturi looks cool and just enough mad scientist to be up my alley. May look into that.

[Bill Waters]

Thanks again, Rasmus. Do you know of a schematic, plans, etc. existing for the slash cut venturi system you describe? I certainly understand the principle and can fabricate pretty much anything I need, but it would be great to have a well-sorted design so that I can limit the experimental phase. After all, we are all already 818 beta-testers!

Thanks,

Bill

[Rasmus]

Thanks again, Rasmus. Do you know of a schematic, plans, etc. existing for the slash cut venturi system you describe?

I'll sketch one up.

[Bill Waters]

Thanks

[Rasmus]

http://i162.photobucket.com/albums/t278/RasmusHansen/Factory%20Five%20Racing%20818R/ExhaustVenturiCrankCaseVacuum.jpg
Rasmus' Idea of an Efficient Crankcase Ventilation System (http://i.imgur.com/HkAMYUP.jpg)

http://i162.photobucket.com/albums/t278/RasmusHansen/Factory%20Five%20Racing%20818R/IMG_0461.jpg
Where ports 1 and 2 are on a 2006 WRX EJ255 case.

http://i162.photobucket.com/albums/t278/RasmusHansen/Factory%20Five%20Racing%20818R/IMG_0463.jpg
Another view of port 2

http://i162.photobucket.com/albums/t278/RasmusHansen/Factory%20Five%20Racing%20818R/IMG_0464.jpg
Another view of port 1

[ssssly]

I wonder what pressure the Venturi would draw. IE what the psi rating for the check valve and related tubing would have to be.

[Bill Waters]

Thanks very much, Rasmus: this is really helpful. Regarding the slash-cut venturi, I presume 45-degree entry of the venturi tube into the exhaust pipe and 45 degree slash (rendering an opening which is downstream to exhaust flow and perpendicular to the wall of the exhaust pipe) is the most effective. Searches on the topic yield only non-authoritative discussions and opinions. Have you seen any reliable info on that?

I really appreciate your always going the extra mile to help.

Bill

[Rasmus]

Regarding the slash-cut venturi, I presume 45-degree entry of the venturi tube into the exhaust pipe and 45 degree slash (rendering an opening which is downstream to exhaust flow and perpendicular to the wall of the exhaust pipe) is the most effective.

http://i162.photobucket.com/albums/t278/RasmusHansen/Factory%20Five%20Racing%20818R/SlashCutInstall.png
I don't know if it's the most effective. I do know that's the common wisdom on how to install it. It's High School Physics Science Project Time! Get a bunch of straws, cut 'em up and see what angles and cuts pull the most vacuum in a known flow.


http://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/pipeflow/pipepressure.gif
I do know fluids in a pipe flow the slowest right near the walls. There's shear forces slowing stuff down. So, for me, in a 3 inch exhaust I'd get the venturi tube opening in there about 5/8" to 1" off the wall, measured perpendicular. The faster the exhaust flows over the slash-cut tube's opening the more vacuum it pulls. Which is way this method works great under boost or at WOT; you're pushing a lot of fluid, very fast, past that opening. Installing it in half-way (1.5") seems over-kill.

[Xusia]

Probably a stupid question, but someone has to ask them: If there is an OEM air/oil separator, why is an external one needed? Please explain the problem we are trying to solve. In a language someone like me can understand! :)

[Rasmus]

Probably a stupid question, but someone has to ask them: If there is an OEM air/oil separator, why is an external one needed?
I like the brain on you Xusia. That is an excellent question.

The OEM air/oil separator is not terribly effective when someone starts pushing these motors to the limit. With frequent boost (autox, track day), High G cornering, and hard braking,; one can easily overwhelm it. If you've ever opened up your inlet tube, turbo, inter-cooler, and/or intake manifold and seen oil coating everything you realize how easy you can overwhelm the system. Not only does everything get oily, your intercoolers efficiency is reduced from the oil coating. Worst of all, sucking oil into the combustion mix reduces the octane rating of your fuel causing knock. Knock is what blows motors and spins bearings.

So what I'm trying to do is keep my parts that aren't supposed to be oily from getting oily, prevent my motor from going boom, and keep my engine's oil off the track.

[Mitch Wright]

FYI if you plan to race the car in NASA or SCCA you might check the rule books, I know at one time a slash cut system were not allowed so it will be worth checking.
They do work, we did see small bump in the dyno numbers with it connected on our GT3 Datsun a number of years ago. We had to take it off when we had a tech inspector who knew his stuff notice it.

[Rasmus]

http://i162.photobucket.com/albums/t278/RasmusHansen/Factory%20Five%20Racing%20818R/IMG_0466.jpg
Here's a better view of the OEM in-case Air-Oil Separator. (http://i.imgur.com/JjKbQUE.jpg)Yep. That's it.

Notice how there's nothing for the oil to condense onto. It's separated into an upper and lower half with the case gasses entering in the lower half. They pass by the edges of the baffle and enter the upper half where the condensing is supposed to occur before making it's way up to the PCV one-way check valve and then into your turbo inlet tube. Your turbo compressor wheel sucks it up. Passes it though the inter-cooler, throttle-body, then intake manifold. Finally getting burned up in the combustion mix.

http://i00.i.aliimg.com/img/pb/764/651/587/587651764_867.jpg
I suppose one could put one of those stainless steel coil kitchen scrubbers in the upper-half. It'd at least give the oil in the crankcase gasses more surface area to condense on. Plus every time you heard a funny noise coming from your motor you'd think it got loose and the oil pump's trying to pass it like a kidney stone. Ahh, the wonderful pucker factor. :D

[Rasmus]

FYI if you plan to race the car in NASA or SCCA you might check the rule books..

Well curses.

Just checked the 'Prepared Class' sections of the SCCA Solo Rules and:

17.10.K.2. The installation of any type of vent or breather on the engine is
permitted. Crankcase, oiling system, breather, or catch tank evac-
uation systems that are in any way connected to the exhaust sys-
tem are prohibited.


So that's right-out for me as I plan to run X Prepared. Glad someone reigned me in.

[Mitch Wright]

It was hard to see on our GT3 car which is not the case on the 818.

[Xusia]

Stupid question #2: If the OEM separator is plumped into the turbo inlet (presumably because there is a vacuum there), why not just plumb an external AOS inline there? Seems like a lot less work, and you still get a vacuum to assist with drawing the air through the separator. What am I missing??

[Rasmus]

Stupid question #2: If the OEM separator is plumped into the turbo inlet (presumably because there is a vacuum there), why not just plumb an external AOS inline there?

It's not a stupid question. That's probably exactly what I'm going to do now, seeing how the SCCA banned my idea long before I came up with it. I don't want the added expense or complexitiy of a seperate vacuum pump just for the crankcase so the only other easy source of vacuum is the turbo inlet pipe.

http://www.jegs.com/images/photos/700/710/710-85474.jpg
I'll just run a quality AOS plumbed just like you described it. Something like the Moroso "Large Body" unit.

[longislandwrx]

Stupid question #2: If the OEM separator is plumped into the turbo inlet (presumably because there is a vacuum there), why not just plumb an external AOS inline there? Seems like a lot less work, and you still get a vacuum to assist with drawing the air through the separator. What am I missing??

That's how most of them work. Tying into the exhaust for vacuum just means you have zero chance that oil is going to be sucked beck into the engine.

[ruckus racing]

Not trying to rip on grimmspeed, but ive had their AOS in hand and the one offered fron S2 performance, and they are just about identical, except the price

[StatGSR]

to be fair, S2 did blatantly copy/steal the Grimmspeed AOS design. That said, i even find the $200 price of the S2 AOS to be completely offensive for what your getting.

[DruOdil]

I just got a used/ like new Grimmspeed air oil separator for $150. I really like the simple design that returns the oil to the crankcase. Simple and no maintenance.

[ruckus racing]

Not sure of the validity of the argument, but I picked up the GS piece in the group buy when it first came out thru RS25.com, and members were stating that the S2 piece had been out before, and it does even come in the same packaging.

Got my S2 on ebay for 164 including shipping to Hawaii

[StatGSR]

Not sure of the validity of the argument, but I picked up the GS piece in the group buy when it first came out thru RS25.com, and members were stating that the S2 piece had been out before, and it does even come in the same packaging.

Got my S2 on ebay for 164 including shipping to Hawaii

the GS unit was out before S2 unit, the S2 is a copy

[ruckus racing]

Well, they do come in the exact same packaging, with the exact same contents

[mekohler]

I went with a dual catch can setup made by saikou michi, had good reviews on the wrx forums. Here is a link to it
http://www.saikoumichi.com/DC3_page.htm
Price is reasonable and the quality is nice.

[DMC7492]

Can this thread and C Plavan's thread be combined so all this info is together?

[DMC7492]

Here is some more Air Oil Separator information!!

[RetroRacing]

If anyone want a barely used GS OAS, let me know and I'll send it to your for $100. We went drysump on our R.

[eggman]

Retro, I'll take that AOS if it's still available.

[FFRSpec72]

If anyone want a barely used GS OAS, let me know and I'll send it to your for $100. We went drysump on our R.

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

[Sgt.Gator]

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?

[FFRSpec72]

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

[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-Comp-Air-Oil-Separator-AOS-Subaru-WRX-STI-p/iag-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.