IAG Performance IAG-ENG-7150RD Red Street Series billet aluminum AOS Air Oil separator vents crankcase vapors back to the turbo inlet. The design is based on years of service on racing and high horsepower Subaru’s. IAG’s AOS has a 1-liter capacity, fully heated housing, superior breathing, and unique patent pending baffle design that sets it apart from the competition. This can even be installed on a 100% stock vehicle with no tuning required.


  • Ready To Install
  • Hardware, Lines & Fittings Included

The IAG-ENG-7150RD 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.


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 no 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.

Q: Which AOS is right for my vehicle?
A: It is IAG’s opinion (which may differ from some builders and tuners) that you should use the following parameters to decide which AOS is correct for your vehicle:

  • Less than 600 WHP on pump gas – IAG recommends the Competition Series AOS
  • 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
  • 100% Stock (no mods whatsoever) on pump gas – Street 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.