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Air Oil Separator for WRX/STI


3 Hours

Part Numbers
PSP-ENG-605BK = 02-07 WRX/STI TMIC Black
PSP-ENG-605RD = 02-07 WRX/STI TMIC Red
PSP-ENG-606BK = 08-14 WRX/08-18 STI TMIC Black
PSP-ENG-606RD = 08-14 WRX/08-18 STI TMIC Red
PSP-ENG-607BK = 02-14 WRX/02-18 STI FMIC Black
PSP-ENG-607RD = 02-14 WRX/02-18 STI FMIC Red

WARNING: This product can expose you to chemicals, including Lead, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to

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Sale: $396.00
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The PERRIN Air Oil Separator traps oil from the crank case vents before it enters the intake, increasing intercooler efficiency, and reduces chances of performance-robbing detonation.

Installation Gallery

Increase Intercooler Efficiency

The AOS 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.

Reduce Detonation

The octane level of oil is very low. Anytime there is a significant amount of engine blow-by (oil) being put back into your engine, it reduces your fuel's octane level leading to detonation or knock, which will cause loss of power and engine failure.

PCV System Included

We designed the PERRIN Air Oil Separator kit based on the idea that using a PCV on the AOS outlet ensures proper crank case venting during light loads and helps reduce unwanted blow-by gases into your intake system. Incorporating a PCV reduces the smell from exhaust and keeps your intake tract clean.

Easy Disassembly For Cleaning

Over the years, a slight buildup may occur inside your AOS. This can be quickly taken care of by removing one bolt to access the inside for cleaning. This small feature is one of the many things that makes the PERRIN AOS stand out from the rest.

Swirl Pot Technology

Featuring swirl pot type technology and multi-layer baffles, the PERRIN Air Oil Separator forces incoming air to circulate across the baffles, separating oil from engine blow-by.

This is not a catch can

The PERRIN Air Oil Separator is not a catch can. Catch cans capture water and oil vapor filling with a sticky mess requiring it to be emptied. The PERRIN AOS separates engine oil from water vapor and allows it to drain back into the engine. Oil entering from the crankcase vents spins counter clockwise through the entire body of the AOS, passing along four walls equaling roughly 50.25 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!

As oil accumulates on all the walls, gravity pulls it to the bottom of the can where it drains back to the engine block while water vapor and air merge with the intake air and are re-burned in the engine. This means little maintenance or upkeep.

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 AOS body, the drain fitting is threaded to except virtually any kind of fitting to allow for easy customization on special projects.

Heated By Coolant

The base plate of the the AOS is heated by coolant drawn from the engine. By keeping the AOS the same temperature as the engine and blow-by gases, water condensation is decreased allowing oil and water vapor to separate and pass through the can.

This vital feature eliminates nearly all the sludge that can build up in the AOS body, which drastically reduce how often you must clean it.

Hardware and Parts

Every connection on the PERRIN AOS is threaded NPT which is a very universal way to connect fittings. This allows for totally customizable setups and installations to be done, to best match your setup.

Application Specific Mounting Brackets

Each kit comes with specific mounting brackets and instructions to install your AOS perfectly in your engine bay or adapt our simple 2-hole mounting bracket for custom installations.


Powder coated for protection against the elements, the textured finish will look awesome for years to come. The PERRIN AOS is available in black or red texture powder coating.

Subaru Specific

Subaru engines have 3 main crank case vents located on each valve cover, and one in the center crank case.

The PERRIN AOS 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).

5 Year Warranty

PERRIN Performance warrants to the original purchaser that all PERRIN products will be free from defects in material and workmanship within a sixty (60) month period from the date of purchase. *Some exclusions apply
» Read Full Warranty

Off Road Use Only

This product is legal in California only for racing vehicles which may never be used upon a highway. Check your local and federal laws prior to installation!
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Warranty Details

This product features a 5 year warranty Read Full Warranty

Tech Department


In The Box

In The Box

(1) PERRIN Air Oil Separator
(1) Car Specific Bracket
All necessary hardware
(1) PERRIN License Plate Frame

Compatibility Detail


2002-2007 Subaru WRX Yes, see Note 1
2008-2014 Subaru WRX Yes
2004-2007 Subaru STI Yes
2008-2014 Subaru STI Yes
2015-2018 Subaru STI Yes
2015-2018 Subaru WRX No
2005-2009 Subaru Legacy GT Yes

Note 1: 2002-2005 WRX installation requires the removal of cruise control module.

General Note: For left hand drive cars only.


Shipping Information

  • Item Requires Shipping
  • 8.0 lbs.
  • W7.0000” x H13.0000” x L20.0000”
  • This item ships in its own box.