The IAG Performance Competition Series billet aluminum Air / Oil separator (AOS) vents crankcase vapors to the atmosphere. 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 sets it apart from the rest.
*May require tune recalibration.
- 180° Breather Port Rotation For Install Ease
- Large Breather Port
- Greater Pressure Stream Oil Separation
Notice the large breathing 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 diameter 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 Powder Coated Black, Red, Gold and Dark Silver. Also available in World Rally Blue (automotive paint).
The side of the Air Oil Separator 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 breath without disturbing the swirl pattern.
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 of 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.
AOS IN THE BOX
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.
- Ready To Install
- Hardware, Lines & Fittings Included
Q: Why do I need an AOS?
A: In stock configuration, the un-baffled crank case pressure is re-circulated back into the intake stream. This can be harmful for two reasons:
1) Oil vapor mixed with the intake air effectively lowers the overall octane rating of your fuel. The more oil vapor that is sucked back into the engine, the more likely you are to experience engine knock (also referred to as detonation) that can destroy an engine.
2) Oil vapors cause oil & carbon build up over time. The intercooler, intake manifold & intake valves suffer the worst. This oil vapor can create air turbulence that leads to various running issues.
Q: What are the factors that cause oil in crank case vent system (CCVS)?
A: There are a variety of factors that determine how much oil will be in the CCVS. The most significant of these factors are boost pressure, piston to cylinder wall clearance and oil viscosity. Smaller factors include ambient temperature, engine temperature, piston ring condition and valve guide condition.
Q: Are there any risks to using the IAG billet AOS?
A: If your AOS is properly installed, there are not any risks.
Q: What's the difference between a catch can & the IAG AOS?
A: Catch cans are an air/oil separator that does not actively drain the collected oil back into the engine. Most catch cans require you to drain the contents out manually. While acceptable on some engines that produce little oil in the CCVS, the Subaru EJ engine is not this type of engine. By nature, a turbocharged boxer engine will produce significantly more oil in the CCVS than other engines of similar displacement.
*Please note that IAG recommends the STREET SERIES AOS for ALL cars 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.
PDF Instructions for 2017-18 STI IAG Performance Air Oil Separator
PDF Instructions for 2015-16 STI IAG Performance Air Oil Separator
PDF Instructions for 2008-14 STI IAG Performance Air Oil Separator
PDF Instructions for 2008-14 WRX IAG Performance Air Oil Separator
PDF Instructions for 2005-09 Legacy GT
* The IAG AOS is not compatible with most aftermarket strut tower bars.