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.
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 counterclockwise 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!
The base plate of the air oil separator is heated by coolant drawn from the engine. This heats the entire air oil separator to the same temperature as 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.
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 in the combustion chamber, intake valves, and in your intake tract. Crankcase 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.
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.
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.
Our unique crankcase vent fitting places the AOS in the perfect location to maintain the ideal temperature while staying out of the way of aftermarket TMIC's, FMIC's, charge pipes, master cylinder braces, and cold air intakes.
Included with the PERRIN Air Oil Separator for 2015-2023 WRX, the PERRIN Turbo Sump Pump Restrictor fixes burning oil issues relating to turboback exhausts or Stage 2 and higher tunes. Click here to learn more.
Powder coated for protection against the elements, the finish will look awesome for years to come. The PERRIN Air Oil Separator is available in black, red, or neon yellow powder coating.
Subaru EJ engines have 3 crankcase type vent locations that are on the valve covers and center of the engine block. Subaru FA engines have 2 crankcase vent locations, both located on the engine block. 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 (a common issue on flat-type or boxer engines).
Increase horsepower and torque without ECU recalibration or tune! This part is designed and tested to work safely on your vehicle without any tuning required! However, more power can be gained with proper ECU tuning! Confirm any tune or recalibration you add is specific for ALL modifications added to the vehicle. Questions? Contact [email protected].
(1) PERRIN Air Oil Separator
(1) Car Specific Mounting Bracket
(1) PERRIN License Plate Frame
All necessary hardware for installation
Warranty & Instructions
* 2002-2007 WRX - 2002-2005 WRX installation requires the removal of the cruise control module
* 2015-2021 WRX - Modifications may be needed if installed with an after-market air intake box, contact tech for further details
* 2015-2021 WRX- Does not work on vehicles with EyeSight
*For left-hand drive cars only
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
WARNING: Cancer and Reproductive Harm
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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