top of page

Vehicle Fitment:

Subaru 2006+ WRX/ 2004+ STI



PriceFrom $439.99
  • The IAG Performance Street Series billet aluminum Air / Oil separator (AOS) vents crankcase gasses back to the turbo inlet. The design is based on years of service on racing and high horsepower Subaru's. The AOS's approximate 1-liter capacity, fully heated housing, superior breathing, and unique patent pending baffle design set it apart from the rest.


    • Breather Port Rotation For Install Ease
    • Dual Breather Port
    • Greater Pressure Stream Oil Separation

    Notice the dual breather port? At first glance you might think this is excessive, however, our reasoning is grounded in simple physics. As air and particles of oil enter into the AOS, the largest particles of oil will collect on the inner surface of the can and drain to the bottom, but the smallest particles will remain suspended in the pressurized stream.

    As the air makes its way through the multi-stage baffle system, gravity pulls oil from the air. By increasing the overall volume of the breather opening on the top of the AOS, we have drastically decreased the exit velocity of the crankcase vent (CCV) stream. The slower velocity leads to greater oil separation from the pressure stream. A total of 9 mounting holes enables the breathing port a full 180° of rotation. On the bottom, a thick Viton o-ring seals the can. Every o-ring in our AOS is formed from Viton which offers superior temperature and chemical resistance.


    • Large Billet Aluminum Design
    • Approximate 1 Liter Holding Capacity
    • Integrated 3 Port Billet Hose Barbs
    • Aluminum Body is powder coated in Red, Black, Gold, Dark Silver. Also available in World Rally Blue (automotive paint).

    The side of the AOS features 3 port billet hose barbs. There are NO plastic fittings that require thread tape to seal.

    The Subaru EJ engine has 3 ports that vent crank pressure: one on each cylinder head and another on the top of the block. Each engine vent port receives its own connection to the AOS. By giving each engine port its own entrance to the AOS we have allowed for more effective and faster excavation of crankcase pressure. Additionally, this reduces overall system pressure. With a 4" OD and 5.75" height, the AOS has an approximate 1 liter of holding capacity. The larger the AOS, the more power you can safely make without having to worry about the AOS overfilling.


    • Unique Baffling Controls Crankcase Pressure
    • Returns Oil To The Engine
    • No Maintenance or Manual Draining Required

    The bottom of the AOS is shaped like a snail, redirecting positive crank pressure into the same swirl pattern produced by the 3 side ports. Allowing maximum oil drainage while separating oil from the air in all the venting ports.

    Why not use a catch can? Unmodified Subaru's may require catch can draining as often as every few weeks. Heavily modified race cars may be as often as every race.

    Our AOS collects oil and actively drains the oil to the crankcase. The drain port is under the same crankcase pressure as the other ports that are on the side of the AOS. Under normal, off boost driving the weight of the collected oil will easily overcome the pressure in the drain line. However, under heavy boost (especially on higher powered engines) the crank pressure will push back up the drain with the same air/oil mixture that is seen on the side ports. The unique snail design allows the system to breathe without disturbing the swirl pattern.

    The AOS drain port is able to be rotated for ease of installation.

    All fittings supplied with the AOS are anodized aluminum and feature Viton sealed ORB fittings.

    The supplied coolant hose is built to SAE 20R3 standards. It will withstand coolant temperatures of +257°F. The oil vapor hose is designed to withstand oil and fuel vapors, exceeding SAE J30R7 standards.


    • Heated By Engine Coolant
    • Reduces Moisture & Oil Mixing

    The back plate of the AOS features a unique coolant routing system that heats the entire AOS to the same temperature as the engine. This maximizes the evaporation of any water collecting inside of the can. The hotter the AOS, the less water will collect inside and mix with the oil.


    • Multi-point Adjustable Mounting Bracket

    The center bracket allows for adjustable mounting. If your engine bay changes, you can easily change how and where you mount the AOS. A single laser-cut mounting bracket is included that fits nearly all applications and configurations.

    A laser cut harness relocation bracket is also included. The bracket allows the engine harness connector to be moved forward for additional clearance.


    • Ready To Install
    • Hardware, Lines & Fittings Included

    The AOS arrives completely assembled and ready for immediate installation. However, the entire unit can be broken down for cleaning. With a single allen wrench, you can remove 4 bolts and the AOS easily separates into individual pieces.

    • Less than 600 WHP on pump gas – IAG recommends the Competition Series AOS. The Competition series provides the best venting of the PCV system and also prevents any oil suspended in the PCV gases from re-entering the turbo inlet. If you prefer not to retune the vehicle for installation of the AOS, the Street Series may be used below 600 WHP.
    • Less than 600 WHP on E85 – IAG recommends the Street Series AOS
    • Greater than 600 WHP on E85 / PUMP GAS / RACE GAS – IAG recommends the Competition Series AOS

    *Please note that IAG recommends the STREET SERIES AOS for ALL cars under 600 WHP running E85 or high-ethanol fuel blends. When tuning E85, ethanol vapors tend to stay in the crankcase, which ultimately results in the oil becoming diluted and requiring extremely frequent oil changes. Pulling vacuum via the Street Series recirculating design to the inlet is ideal for ethanol tuned vehicles, and will allow the ethanol to be removed from the crankcase and burnt off as part of the combustion process. When running greater than 600 WHP on E85 IAG recommends the COMPETITION SERIES AOS and 1500-2000 mile, or every race event, oil change intervals. Please note that the COMPETITION SERIES AOS at any power level will require a custom tune.

bottom of page