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AOS - Do all of you run one?


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I was hot to trot to get an AOS at one point but have sort of fallen off on buying parts for my '06. It's got over 100k miles on it and still seems to run fine.

Is installing an AOS (like the pricey IAG one) a good thing to do?

I kind of hate how much it adds to the piping under the hood, but my tuner recommends them.

 

The full on IAG one is pricey and seems fairly complicated to install. A lot of WRX guys are running catch cans, but nobody seems to make any for the turbo Legacy platform.

 

School me on AOS/Catch Cans. Thanks!

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Crawford AOS installed on my recent build and I am happy with it so far. I wanted as little of that oil crud in the intake as possible.

 

Read about them and make your own assessment. They seem to be a touchy subject 'round these parts.

 

Sent from my SM-G996U using Tapatalk

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by the time you actually *need* an AOS, you aren't getting advice from the internet.

 

Does it help? Does it hurt? no.

 

I had one of the original ones that ran off the oil cap. A variety of shops told me it would cause problems and blow my engine. the only problems i had were from techs applying 100lbs of torque to the 19mm bolt head of the filter cap destroying the o-ring that kept it sealed. It was meant to be hand-tight (15lbs). 28k miles of track driving later, there was no indication of any improvements from running it. ymmv.

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I have a Crawford and its a serious install since it has coolant running through it. In fact I pulled into the gas station yesterday and one of the coolant lines was blown and I had lost quite a bit of coolant. The engine never overheated, I added coolant and a new line and all is good. Its a bit of spaghetti tubing wise and the hose that was bent too far didn't look like it. I think time and heat cycles and a little too much bend got me. Easy fix and happy I was in town and not out in the mountains when it happened. I now have a couple feet of coolant line in the spare tire area just in case.

 

Performance wise my intake is mostly dry and clean. Nothing like it used to be.

 

FWIW - I would install a cylinder 4 cooling mod first for longevity over an AOS.

Edited by VespaGTS
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I have the IAG, I don't think they are really necessary for a street car with a stock or near stock setup. But "H" engines lack the height to separate the air-oil mix well, so it cant hurt.

 

I did modify the installation a little, I kept the head to head crossover pipe (modified) so I could run one line from center instead of two from each head. I also only have one suction line in front of the turbo, instead of two. The air flow of the system might be a little lower configured this way but more than enough for a street car. I also changed the mount a little to get it as high as possible in the engine bay, this way I could route the drain line with a continuous slope back to the block. And the engine cover still fits!

 

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Is installing an AOS (like the pricey IAG one) a good thing to do?

 

 

School me on AOS/Catch Cans. Thanks!

 

 

No. You need neither. If you want to waste some money install a set of catch cans and see how little oil ever makes it into the cans.

 

 

 

Running high compression and big boost? Then get a good AOS. But your builder should already know this when putting together your monster.

 

 

 

Only a handful of cars actually need an AOS. Build a real monster and the AOS does nothing but blow oil all over the track from beneath the car. Graph is Cali piss water 91 ACN. I have the e85 graphs somewhere... Car ran so hard it would vapor lock when hot prior to installing the flex fuel and fuel pressure sensor set up. After that you could finally run full tilt all day.

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Edited by m sprank
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I will propose the idea that an AOS night be useful to extend the use of a high mileage engine.

 

My original engine went to 305,000 miles (all stock) and was retired due to knock caused by oil in the intake. I did not have the AOS at the time, but I suspect that it would have helped.

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Running a Crawford AOS in the track car because at this point the motor sees pretty much high rev, gas pedal to the floor driving conditions whenever it’s used. Don’t see that the OEM PCV system is a bad thing on your typical street car as long as it’s functioning properly so staying stock on my daily stg2 Outback
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I run the IAG, I don't know if it does any good or not...my intake is clean as a whistle. As to whether or not you need one....who knows, but it can't hurt if you want to spend the money.

 

Running an AOS can absolutely hurt your engine if you live in a cold climate. Lines can freeze up and cause the crank case pressure to skyrocket and push out seals. I had a freeze up push out cam seals and I lost all oil and oil pressure. I was lucky that I didn't end up with a spun bearing.

 

There is a reason that Crawford has various revisions to their AOS, people had issues with them freezing. They still sell the unheated version for race only but even with a heated can you still need to be very careful in the cold. Other companies only sell unheated versions and claim there are no issues but people have had issues with them, and likely will again.

 

I'm not saying that cold weather automatically means you shouldn't run an AOS, or that you will have problems, but it is not as easy as saying throw it on your engine and all will be good. As long as you understand the risks and know what to look for and how to deal with it, you should be ok but the risk is still there.

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  • 3 months later...

I've installed one in my new STI and plan on putting one in the spec b with the new engine.

If you ignore the marketing wank, oil vapor from the pcv system going back into the intake can and will reduce octane rating of the gas going in. May be a little..may be a lot depending on a lot of factors. Also keeps the entire intake system cleaner. 

I don't know any subie/porsche engine builder that would specifically say NOT to install a good one like the IAG street series. 

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