COBB Tuning Air Oil Separator Black/Red - Subaru Models (inc. 2008-2021 STI / 2008-2014 WRX)

Keep Oil Out of Your Intake Charge

The Cobb Air Oil Separator for the 2008-2021 Subaru WRX STI captures the oil vapor that the factory PCV system vents back into the intake path and separates it before it reaches the turbocharger and intercooler. On a turbocharged Subaru EJ or FA engine, PCV oil vapor coats the inside of the charge pipes, intercooler core, and intake manifold with an oil film over time — reducing intercooler efficiency and introducing unwanted hydrocarbons into the combustion charge. The Cobb AOS collects the oil, drains it back to the sump, and keeps the intake path clean. This listing is the Black variant.

Why PCV Oil Vapor Is a Problem Worth Solving

Every turbocharged engine produces blow-by — combustion gas that slips past the piston rings into the crankcase. The PCV system vents this blow-by back through the intake to be burned in the engine, but on a modified GR/VA STI running elevated boost, the volume of blow-by increases and brings more oil vapor with it. That oil doesn't burn cleanly — it deposits on the intercooler fins, reducing cooling efficiency, and on the intake valve stems, contributing to carbon buildup. The Cobb AOS addresses the problem before it reaches those components.

Bolt-In Installation — Drains Back to the Sump

The Cobb AOS installs in the PCV line between the engine and intake on the GR/VA STI. The separator catches oil vapor, condenses it to liquid, and drains it back to the oil sump through a return line — no manual draining required. Installation uses factory connection points and requires no modification to the engine or intake system.

Key Features

• Platform: 2008-2021 Subaru WRX STI
• Captures PCV oil vapor before it reaches the turbocharger and intercooler
• Automatic drain back to sump — no manual servicing required
• Installs in factory PCV line — no modification to engine or intake
• Keeps charge pipes, intercooler, and intake manifold free of oil film
• Available in Black finish

Fitment Notes

• Platform: 2008-2021 Subaru WRX STI
• Installs in factory PCV line — no modification required

Straight From Subispeed

The Cobb AOS is one of those purchases that solves a problem you can't fully see until it's already happening inside your charge pipes. On a modified GR/VA STI with elevated boost, the PCV system vents more oil vapor than stock — it's not a question of if it'll coat your intercooler, it's a question of how fast. The Cobb AOS stops that before it starts and earns its cost by preserving the intercooler efficiency your tune was built around.

What's Included

• Cobb Air Oil Separator — 2008-2021 Subaru WRX STI
• All connection hardware and drain line

About Cobb Tuning

Cobb Tuning has been developing performance parts and tuning solutions for Subaru vehicles since 1999. Based in Austin, Texas, Cobb built their reputation on the Accessport — the most widely used Subaru ECU tuning device on the market — and expanded that into a full ecosystem of intake, exhaust, drivetrain, and engine bay accessories engineered specifically for the platforms they support. Every Cobb product is developed in-house and validated on their own test vehicles before it reaches customers. Subispeed carries the full Cobb catalog because their engineering standards and platform-specific development process consistently produce parts that work exactly as advertised.