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Old 07-12-2011, 09:15 PM   #1
monkiboy
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Join Date: Feb 2009
Chapter/Region: MAIC
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Vehicle:
2008 wrx

Default catch can / AOS setup for autox

hi -

i have an 08 wrx that i autocross in SM about three times a month. this is also my daily driver. it's about 350whp now and and will be going to about 490whp soon.

i have a grimmspeed AOS installed. it seems that the tight fast corners of the autox course is flooding my heads with oil and my AOS is seeing the worst of it.

i was running the black rubber hoses for a while and last week added small sections of clear hose so that i could SEE how the AOS was performing.

the AOS is installed per grimmspeed's instructions.

you can see in the photo that the center hose that is connected to the breather hose that is connected to the inlet has a good deal of oil in it.



notice the pool of oil at the bottom of the center hose that is connected to the blue hose to the breather to the inlet.



here's another photo



i am looking for a solution specific to those of us in the autocross community that have to deal with these kinds of symptoms.

i believe that i am more inclined to use a system that one does not drain as i feel the catch can would become filled very quickly and i dont want to deal with possible oil starvation.

i would like a system that will be able to do its job effectively at 450+whp. i have seen dual tank setups (one for the PCV and one for the breather ports which are tee'd off) both connected to the inlet for vacuum and these seem like they might work well.

i see systems that VTA (element tuning/peterson can) that can or cannot be setup to be drained.

there is the crawford that a lot of track guys use but that eliminates the PCV which most knowledgeable builders tell me i should keep.

i guess i would like to know what those of you with higher HP cars that are autocrossed and daily driven have as your AOS/catch can system? how has it functioned for you, what would you change, etc. then what would you recommend for my application and why given the information i have provided.

thanks for any help you can provide as i have yet to find a credible answer and most gurus/mods i asked on this board told me to post here.

look forward to your replies!
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Old 07-13-2011, 09:45 PM   #2
Gearz
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I have an '08 STI set up for STU class with the Grimspeed AOS like yours. I still get some oil in the intercooler after events with long runs at the top of 2nd gear. I installed an additional catch can between the AOS and the inlet and sure enough, it gets oil in it during autox.

Here's what I think is happening. In '08, Subaru went to adjustable valve timing on the intake and exhaust cam sprockets. In order to provide the oil pressure for the VVT actuation system they upgraded the oil pump to a high-volume unit. At high rpms I believe it is pumping the oil out of the pan faster than it can drain back. Coupled with high lateral G's it's easy to see how the cylinder heads could fill with oil or at least enough to get quite a bit splashed up into the breather tubes. Add to that positive crankcase pressure from full boost blow-by and you have a mechanism that puts a lot of oil into the breather tubes. The Grimspeed AOS is designed to let gravity pull the liquid oil down the filler neck while letting crankcase pressure escape up and into the intake. The problem is with so much volume and vapor it just can't separate the oil fast enough, or, it could be that the oil in the cylinder head fills up the filler tube as well and gets forced out of the vent line. Either way, I'm seeing the same thing you are. I don't think the WRX motor has the high volume oil pump but then you're probably running a lot more boost than I am, which increases the crankcase pressure.

There are two problems you need to fix. First, if you want to continue with the vent system you have (PCV and vent line to intake) you'll need another catch can in the vent line after the Grimspeed AOS. I'd recommend the Crawford unit with drain back to the crankcase. Second, you need to add an Accusump to prevent oil starvation if the pump is draining the oil pan during long 2nd gear runs with high lat-G's. The event that killed my engine had a fast 6-cone slalom and a high speed run up to it. After my 2nd run the engine was knocking. After that rebuild I short-shift into 3rd in courses like that.

Maybe not what you wanted to see but that's my advice based on my experience. I'm curious if Subaru made any changes to the 09-11 engines to address the oiling issue at high-rpm.

-Brian Meyer
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Old 07-14-2011, 03:23 PM   #3
wantsti
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I have the same problem in my 04 sti. I contacted grimmspeed and they said they were working a a version 2 to fix this problem. I'm thinking with the high g forces and the back and forth its pushing oil up the feeler tube into the the intake.
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Old 07-15-2011, 01:16 AM   #4
monkiboy
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2008 wrx

Default

thanks a lot for the replies guys, i am very glad to hear that i am not alone in this battle with the GS AOS and my autox'ing experiences.

what wantsti is my experience as well. i spoke to will and they mentioned they should have something soon but no specific leads dates. for the time being this is NOT working during my autox sessions and it can only take one event and the right mix of variables to have a serious problem.

i'm gonna temporarily remove the GS AOS, swap to a greddy catch can, and route it to the crankcase vents tee'd off and then the inlet for vacuum. i'll keep an eye on levels of the catch and of my motor's oil. if too much starts to accumulate after a session, then i'll tap it for drainback to the crankcase.

the new GS AOS that will solve these problems should be out relatively quick. if not within a couple months, i will run what i think is ideal - dual saikou michi cans.

please do not determine this as a conclusion to the post.

i am very interested in hearing solutions that people with this problem have come up with or catch can/AOS solutions that are working well for autox drivers that have had their system in place for a duration of time that has allowed them to determine their system is functional.

thanks, again!
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Old 07-20-2011, 09:22 PM   #5
BeBop86
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Interesting... would like to hear more about this too.
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