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Thread: Air Oil Seperators (AOS) and what they do

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    Air Oil Seperators (AOS) and what they do

    Wasnt sure where to put this, so I put this in here.

    After I posted the sale offer for the Grimmspeed AOS, I had a few people message me asking me what these are and what they do. So I am going to try to explain the system and how it came about.

    First of all it started back with the EPA required the automakers to re-route the crankcase vent from venting to atmosphere to venting back into the cars engine to burn off the "harmful" gases. To do this they had to route the vent into the intake system. As you can imagine when venting the gases from the crankcase you are also going to be getting oil mixed into that which is also getting sent back into the engine through the intake. This is called Blow By, what happens is the blow by goes into the combustion chamber via the intake system. When oil enters the combustion chamber it lowers the performance of the car by effectively lowering the octane of the fuel, leading to detonation.

    There are two solutions for this problem.
    1. Air Oil Seperator
    2. Catch Can

    What are these two solutions?

    1. Air/Oil Separators effectively removes the oil from the air coming out of the engine’s ventilation system via a two stage process using chambers in the system. The first chamber is designed to use centrifugal force to remove the oil from the air, the clean air is then pushed into a second chamber and extracted from the AOS to the engine while the oil is recirculated back to the crankcase where it belongs.

    A Catch can is a tank that is put inline of the system to capture the blow by and hold onto it. Once this gets full, you are required to empty the can.

    Ok now you know what these are, now lets tell you features and benefits.

    1.The Air Oil Seperators are more expensive than your average catch can
    2.The Catch Can needs to be monitored to ensure that it does not get too full and stops doing it's job, where as the AOS seperates the two and sends them to their rightful places.
    3. A lot of catch cans on the market dont do a whole lot for the high boost cars due to the air forcing through so fast, however ones with offset ports or baffling fix that problem by giving the air containing oil to run into first creating seperation.
    4. Catch cans not only require you to monitor the tank, but you need to monitor the oil level of the car as well being that it does not return the oil to the crank case.
    5. Catch cans build more moisture specially during climate changes. This can also get into the air.
    6. Some AOS systems that incorporate the tanks also can sweat and build moisture but much less than the catch can and there are companies out there that have designed their systems to minimize/ eliminate this such as Crawford Performance and Grimmspeed.

    You will hear a lot of argument on the web on which is better and so on but our professional opinion it comes down to more of which is more dependable, requires less maintenance, and performs the best. We believe that goes to the AOS because of the design to remove the blow by oil and send it back to the system crank case.

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    ShiftHappensLTi's Avatar

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    Thanks for the info!!!

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    Anytime!!

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    System Operator IGOTASUBARU's Avatar

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    Moved so all can see. Great write up. Going to stick!
    Without you, we cease to exist. Without your support, we stop growing. Without your involvement, we remain at a standstill.
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    And yes you just answered my next buy question being as im going with the FMIC. Spanks man

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