Perrin Air Oil Separator | 2015-2021 Subaru WRX (PSP-ENG-609)

Perrin Performance

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2015-2021 Subaru WRX Air/Oil Separator by Perrin Performance

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 air oil separator is heated by coolant drawn from the engine. The 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.

Turbo Sump Pump Restrictor - Included with the PERRIN Air Oil Separator for 2015-2018 WRX, the PERRIN Turbo Sump Pump Restrictor fixes burning oil issues relating to turboback exhausts or Stage 2 and higher tunes.

Finish - 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 or red texture powder coating.


  • Separates Oil from Air, Draining it Back to the Engine
  • Eliminates the Need for Constant Attention and Draining of Oil
  • Swirl Pot Technology with Multi-Layer Baffles
  • Base Plate Heated by Coolant Drawn From the Engine to the Same Temperature as Blow-By
  • Increases Intercooler Efficiency by Reducing Oil Deposited Into the Intercooler and Intake
  • Reduces Carbon Build Up in the Combustion Chamber, Intake Valves and Intake Tract
  • Low-Profile Aluminum Fittings are CNC Machined and Anodized Black
  • Includes Turbo Sump Pump Restrictor to Fix Oil Burning Issues
  • Powder Coated in Red or Black for Protection Against the Elements

Please Note: Estimated DIY Install Time is 3 Hours.


  • 2015 - 2021 Subaru WRX


  • Reduces Carbon Build-Up
  • Increases Intake Efficiency
  • Increases Intercooler Efficiency
  • Lessens Required Maintenance

What's In The Box?

  • 1 - Air/Oil Separator
  • 1 - Mounting Bracket
  • 1 - Turbo Sump Pump Restrictor
  • 1 - Perrin License Plate Frame
  • Necessary Fittings and Hardware
  • Warranty
  • Instructions
  • Stickers



  • Perrin Worry-Free 5 Year Warranty

Customer Reviews

Based on 11 reviews
Frank Brown
Perrin AOS

While it wasn't the easiest install I've done, the finished product looks pretty tidy under the hood. And the bright green really sets itself apart. Thus is a well designed product, and I'm looking forward to many years of use.

Perrin aos

Must have if you want to keep building your wrx

Caleb Hansen
Great product, looks good, moderate install difficulty

Super fired up on the Perrin AOS, purchased as a supporting mod for the Stage 2 kit! Install takes a little time, but is mostly straightforward. Quick shipping and a great price 👌🏻

Charles Smith
2018 Subaru WRX - Works great so far! Only one real issue.

When installing the Turbo Sump Restrictor there were no 1/4'' not 5/16'' hose components for the fitting on either end. The 1/4'' fitting from the restrictor is supposed to connect to the 5/16'' fitting on the AOS. I had to pick up the 2 different size hoses and made a 5/16'' to 1/4'' hose connector out of some parts at Advance AP (a nice one can be bought online). Wasn't a huge setback, but it would have been nice to have any of that included.

2018 Subaru Wrx

Perrin AOS Great quality, medium install difficultly. Don't recommend installing yourself if you're not mechanically inclined. Will not fit with Cobb BigSF intake box installed. So i removed the box.