Description
Note: For left-hand drive cars only.
The PERRIN Air Oil Separator prevents oil from entering the intake by capturing it from the crankcase vents. This reduces carbon build-up, improves intercooler efficiency, and lowers the risk of performance-degrading detonation.
Maintenance Free Closed Loop Operation
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 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!
Heated by Coolant
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.
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 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.
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.
2022+ WRX - Crank Case Fitting
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.
Finish
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 or red powder coating.
Subaru Specific
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).
No Tuning Required
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.
In the Box:
- (1) PERRIN Air Oil Separator
- (1) Car Specific Mounting Bracket
- (1) PERRIN License Plate Frame
- All Hardware for Installation
- Warranty & Instructions
What Does an Air Oil Separator Do on Track?
An Air Oil Separator (AOS) manages crankcase ventilation by separating oil vapor from blow-by gases before they are reintroduced into the intake. Under sustained high RPM, high G-load, and elevated cylinder pressures, factory PCV systems allow oil vapor - and in some cases liquid oil - to enter the intake tract. On track, that becomes a consistency and reliability issue.
A properly designed AOS provides:
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Improved oil control under sustained lateral/longitudinal G’s
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Reduced oil ingestion through the intake system
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More stable combustion (higher effective octane retention)
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Cleaner intercooler/charge piping on forced-induction cars
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Reduced detonation risk during extended high-load operation
On Track
In HPDE and time attack use, extended high-RPM operation and long sweepers can overwhelm factory PCV systems. Oil vapor reduces effective octane and increases knock tendency - especially in turbocharged or high-compression builds. An AOS helps maintain consistent power delivery across sessions and protects the engine under repeated heat cycles.
In wheel-to-wheel racing, where engines see continuous high load and aggressive engine braking, proper crankcase management becomes a durability component - not just a cleanliness upgrade.
Trade-Offs
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Added system complexity
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Potential installation sensitivity (improper routing can cause pressure imbalance)
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Minimal direct horsepower gain - benefit is in consistency and protection
Recommended For
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Intermediate to advanced HPDE drivers
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Time attack competitors
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Wheel-to-wheel race cars
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Turbocharged or high-compression engines
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Cars seeing sustained high RPM and high lateral G
Not Required For
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Lightly driven street cars
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Occasional spirited driving with short pull durations
Bottom Line:
An AOS is a reliability and consistency upgrade - not a peak power mod. If your car sees sustained high load, high RPM, or high G environments, proper oil vapor control becomes engine protection insurance.