PERRIN Air Oil Separator - Black - 02-21 WRX, 04-21 STI

Crankcase blow-by, made up of oil particles and air, is recirculated into the intake. The PERRIN Air Oil Separator captures the oil before it reaches the intake tract, which helps limit carbon buildup in the valves and combustion chamber. Reducing this buildup helps avoid power loss and lowers wear and tear on the valves.

The PERRIN Air Oil Separator uses two internal airflow methods to remove oil from blow-by. The swirling airflow pulls oil particles out of the air, and the internal grooves, curves, turns, and holes create impact points that catch additional oil for efficient separation.

The 2002-2021 WRX/STI AOS places the unit in an ideal location to maintain proper operating temperature and keeps the AOS clear of strut bars, master cylinder braces, and cold air intakes.

The PERRIN Air Oil Separator isn’t like a catch can. A catch can is like a little cup that fills up with yucky engine stuff, and you have to empty it all the time. An Air Oil Separator is smarter, it separates the oil from the air and sends the oil back into the engine, so you don’t have to keep checking and draining it.

Coolant heats both the top and bottom of the PERRIN AOS, keeping the body at the same temperature as incoming blow-by. This reduces condensation, prevents sludge buildup, and helps oil, air, and water vapor separate. 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 AOS is virtually maintenance free but can be opened with a single bolt when cleaning is needed. This simple design gives quick access to the internal surfaces so any residue can be wiped out easily.

Keeping oil out of the intake and intercooler is essential for maintaining efficient heat transfer. Oil buildup inside the intercooler reduces its ability to dissipate heat effectively, leading to higher intake air temperatures (IAT).

Preventing oil from entering the combustion chamber is critical for maintaining engine performance. When oil enters the chamber, it lowers the effective octane rating of the fuel mixture, which can reduce horsepower and increase the risk of detonation.

All major components of the PERRIN Air Oil Separator are CNC machined in-house from 6061-T6 aluminum for superior durability and long lasting performance.

The PERRIN Air Oil Separator features a ceramic coated finish rated for more than 500°F. Harder than powder coat, the finish is scratch resistant, extremely durable, and acts as a thermal barrier that helps retain heat in the AOS to reduce moisture buildup that can lead to sludge. It also provides strong chemical resistance, so engine oil, blow-by, and other chemicals will not affect the finish.

The EJ AOS features a purpose-built crankcase fitting rather than a universal adapter. The threaded drain fitting accepts a wide range of fittings, which makes it easy to customize for special projects and unique setups.

Each PERRIN AOS includes two styles of stainless steel hose clamps. Choose between low profile or screw drive clamps to match your preference. Unlike standard clamps, these stainless steel options resist rust and are built to last the life of your vehicle.

All PERRIN AOS hose attachment points use CNC machined aluminum fittings. Unlike plastic fittings, they will not snap during installation or fail over time. Each fitting is machined in house and anodized for corrosion resistance and long term durability.