Perrin Air Oil Separator Kit Black w/RHD Bracket (Subaru WRX)

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  • Regular price $904.95
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Note: Includes new PSR Bolt On RHD compatible mounting bracket and hardware.


RHD Mounting Bracket Notes:

  • Spacers are included to allow clearance of the surrounding fuel lines and wiring.
  • Supplied hoses/fittings from certain catch can/AOS kits may not be sufficient to install their product in this new location. Additional hoses/fittings may be required and sourced separately. For example, some cans may only include straight fittings where 90-degree fittings will work best.
  • For 01-07 Vehicles: Cable-Throttle Models with Cruise Control will need the PSR cruise control relocation bracket (sold separately).
  • For 08-14 WRX and 08-21 STI Vehicles: Factory bracket for the engine wiring harness plug is removed. For 08-14 Vehicles this plug will need to be cable tied out of the way. For 15+ STI the OEM bracket can be mounted upside down and the plug reinstalled in a new position.

For more information on the PSR RHD Bracket click here

PSR RHD Bracket Installation Instructions:


The PERRIN Air Oil Separator traps oil from the crank case vents before it enters the intake, reduces carbon build-up, increases intercooler efficiency, which reduces the chance of performance-robbing detonation.


Not a catch can
The PERRIN Air Oil Separator is not a catch can. Catch cans capture engine blow-by and stores it in a container, which requires constant attention and removal of oil every few hundred miles. The air oil separator separates the oil from the air, draining it back to the engine, which eliminates the need for constant attention and draining of oil. As oil drains from the bottom of the PERRIN Air Oil Separator, clean oil-free air vents out of the top to rejoin the intake tract.

Swirl pot technology
The PERRIN Air Oil Separator features swirl pot technology and multi-layer baffles. This design forces incoming engine blow-by to move rapidly across the baffles, separating oil from the engine blow-by. Multiple layers of baffles means more surface area to collect more oil, making for a compact and efficient design.

Oil entering from the crankcase vents spins counter clockwise through the entire body of the AOS, passing along four walls equaling roughly 50 sq/in of surface area. The multiple baffle walls in our compact design simulate the surface area of an AOS that is 13.5" tall!

Heated by coolant
The base plate of the the air oil separator is heated by coolant drawn from the engine. ThIS heats the entire air oil separator to the same temperature of the engine blow-by. By keeping the air oil separator the same temperature as the blow-by, water condensation is significantly decreased, allowing oil, air, and water vapor to separate and pass through the body.

This vital feature eliminates nearly all the sludge that can build up in the air oil separator body, which is a common problem with catch cans and other air oil separators.

Increase intercooler efficiency
The PERRIN Air Oil Separator increases intercooler efficiency by reducing the amount of oil deposited into your intercooler and intake system! As blow-by/oil builds up inside your intercooler, the less efficient it becomes due to less heat being transferred away from your engine. This leads to power loss and detonation, which can be damaging to your engine.

Reduce carbon buildup
Reduce carbon build up in the combustion chamber, intake valves, and in your intake tract. Crank case blow-by is recirculated back to the intake to be ingested by the engine, but in doing so, gets stuck in the intake tract, intake valves, and the intercooler. This builds up over time which causes a loss in power and extra wear and tear on your valves.

CNC Machined Fittings
The low-profile aluminum fittings provided with the PERRIN Air Oil Separator are CNC machined and anodized black for both a clean, sleek look and corrosion resistance. These tough and durable fittings are designed and finished to last the life of your vehicle.


EJ AOS - Custom drain back fitting
Instead of using a universal type fitting, we have designed a purpose built crank case fitting that does the job perfectly. Like the air oil separator body, the drain fitting is threaded to except virtually any kind of fitting to allow for easy customization on special projects.

Powder coated for protection against the elements, the textured finish will look awesome for years to come. The PERRIN Air Oil Separator is available in black, red, neon yellow, or hyper teal powder coating.

Subaru specific
Subaru EJ engines have 3 crank case type vents located on the engine blow and valve covers, and the Subaru EJ engines have 2 crank case type vents. Each PERRIN Air Oil Separator is designed to connect to each of these separately without requiring any T-connections. This allows for better venting and reduces the chance of oil being ingested during high G corners (common issue on flat type or boxer engines).


In The Box:

  • (1) PERRIN Air Oil Separator
  • (1) Car Specific Bracket
  • (1) PERRIN License Plate Frame
  • All necessary hardware
  • Warranty, instructions, stickers


Vehicle Fitment:

  • 2001-2007 Subaru WRX (01-05 Cable Throttle Models require cruise control relocation bracket)
  • 2001-2007 Subaru STI (01-05 Cable Throttle Models require cruise control relocation bracket)
  • 2008-2014 Subaru WRX
  • 2008-2014 Subaru STI
  • 2015-2021 Subaru STI