Capturing Blow-By: AOS v Catch Cans

I thought I would hash out my reasons for my next big mod, keeping oil vapors out of my intake via either an AOS (air/oil separator) or a catch can setup. And really the only difference between the two is what you do with the captured oil. AOS drains the blow-by back into the engine and the catch cans, uhm, catch the oil to be drained manually.




On my 2005 STi, I ran an IAG AOS and it worked great. I would go with them again except I have a cruise control module in the location of where the IAG AOS mounts and I use cruise control all the time. Radium Engineering makes a relocation bracket but I don’t know if it will clear the IAG AOS. Normally I would just go for it and figure it out later, but I want to check out all of my options first.


I would get the street version this time around to keep the system closed and avoid a re-tune.

+Radium Engineering Catch Cans



Radium Engineering makes a dual catch can setup that looks awesome and comes with dip sticks to check the oil level. So you don’t have to pull half the cans off every time you get curious about how much oil is not going into your intake. This was the top contender for me until a friend beat me to the punch.

Once I realized you had to remove the heat shield to empty the cans I was out. I absolutely can not stand messing around with oil anymore. I don’t know what happened, but I would love an bigger oil pan just to increase my OCIs. 😆 It’s only four bolts but I also have no idea how often those cans need to be emptied. And I would still need the relocation bracket. At that price point I would rather have an AOS. Still looks amazing though.

Radium has a universal catch can setup too. I would probably mount it either where my washer tank or battery is currently located. However, as previously mentioned, I don’t care to increase my oil maintenance workload anymore than what it is.

+Radium Engineering Universal AOS



So this brings me to the Radium Engineering Universal AOS. The leading contender. I would mount this one either where the washer tank is or where the fuel filter is located. In fact, I might be able to reuse the fuel filter bracket to mount the AOS. Time will tell but first thing is first, I need to get this battery and fuel filter out of the engine bay. 🙂


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