COBB Tuning Air Oil Separator Black/Red - 2002-2007 Subaru WRX / 2004-2007 STI

Cobb Air Oil Separator Black/Red — 2002-2007 Subaru WRX / 2004-2014 STI

The Cobb Air Oil Separator (AOS) in black and red for the 2002-2007 Subaru WRX installs in the crankcase ventilation system to remove oil vapor and droplets from PCV gases before they enter the intake system. The AOS keeps the intake manifold, throttle body, and intercooler free of oil accumulation on turbocharged Subaru applications.

DETAILS

• Platform: 2002-2007 Subaru WRX, 2004-2014 Subaru WRX STI
• Installs in factory PCV crankcase ventilation line
• Centrifugal separation removes oil droplets before they reach intake
• Reservoir with drain — collected oil drained at service intervals
• Black and red color scheme — Cobb engine dress aesthetic
• Factory-compatible fittings — no engine block modification
• All installation hardware included

AOS Function: Removing Oil from Crankcase Ventilation Gases

An Air Oil Separator (AOS) installs in the crankcase ventilation system between the PCV outlet on the engine block and the intake system. Turbocharged engines produce crankcase pressure from combustion blowby — gases that escape past the piston rings into the crankcase. The factory PCV system routes these gases back into the intake for combustion, but the gases carry oil vapor and small oil droplets with them. Over time, this oil accumulates on the intake manifold walls, throttle body, and intercooler — reducing airflow efficiency and, in extreme cases, contributing to pre-ignition issues. The AOS separates the oil from the crankcase vapors before they reach the intake, trapping the oil in a reservoir for drainage rather than allowing it into the intake tract.

Centrifugal Separation, Drain Reservoir, and PCV Line Installation

The Cobb AOS uses a centrifugal separation chamber that causes the heavier oil droplets to separate from the lighter air/vapor mixture and collect in a drain reservoir. The separated oil can be drained periodically — the reservoir volume and drain interval depend on how much blowby the engine produces, which increases with age and power level. The AOS connects at the factory PCV line locations without modification to the engine block or intake manifold, using factory-compatible fittings. The black and red color scheme coordinates with the Cobb engine dress aesthetic on Subaru EJ-series applications.

What's in the Box

• Cobb AOS unit (black/red)
• PCV line fittings and adapters
• All hardware

Why Choose Cobb Tuning

Cobb Tuning has been developing performance software and hardware for turbocharged enthusiast vehicles since 1999. Founded in Austin, Texas, Cobb built its reputation on the Accessport and expanded into a full catalog of hardware engineered to complement it. Every OTS map is developed in-house on real vehicles, and every hardware product is validated as part of a complete system — not sourced and sold in isolation. That integrated approach is why Cobb produces consistent, reliable results across the builds we see every day.

The RallySport Take

The Cobb AOS for the 2002-2007 Subaru WRX is the engine bay cleanliness upgrade for turbocharged Subaru owners who want to prevent intake tract oil accumulation over time. EJ-series engines are particularly prone to PCV oil carryover on modified builds where crankcase pressure increases with age and power level. The AOS addresses this cleanly at the source.

Fitment

Year Make Model Notes 2002-2007 Subaru WRX EJ20/EJ255 2004-2014 Subaru WRX STI EJ207/EJ257