Killer B Air Oil Separator | 2008-2014 Subaru WRX / 2008-2021 STI (GR-MV3S)

Killer B Motorsports
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WRX/STI Air Oil Seperator by Killer B Motorsports

The goal of this product is simple. To function as its Air/Oil Separator description implies: the removal of oil, in liquid or vapor form, from the vented crankcase gasses. Simple in premise, but function wise there’s a bit more to it. Varying oil droplet sizes, with differing pressure and velocity conditions. Different engines with varying venting characteristics or a street car vs a track or performance elevated engine.

The Killer B Motorsport Air/Oil Separator functions with a vacuum source only, the turbo inlet. This provides the vacuum source for the crankcase. It is in no way effected by the turbo size, in fact a larger turbo that draws more air will improved separator function, compensating for increased venting requirements seen at improved performance levels. 


  • Accelerated flow of blow-by gasses forces suspended oil droplets out of suspension. Centrifugal filtration is a proven process for separation of many particle types and sizes. The application in automotive applications has mostly been in use with high dollar sports cars and racecars.
  • Collected oil drains back into the crankcase where it belongs.
  • Applies vacuum to the crankcase improving ring seal, reducing oil consumption and improving power potential.
  • No media to clean/replaces or baffles to inhibit crankcase flow
  • Made of billet and TIG welded 6061-T6 Aluminum
  • Killer B Motorsport push-lock barb fittings require no hose clamps


  • 2008 - 2014 Subaru WRX
  • 2008 - 2021 Subaru STI

What's in the box?

  • 1 Oil Air Separator 
  • Mounting Hardware and Brackets


  • Manufacturer Standard Warranty

Customer Reviews

Based on 2 reviews
Brian Denmark
Awesome product!

Killer b did an awesome job with the aos! No instructions provided so had a shop do the install just to be safe. Had it for a while now no complaints works as it should! The craftsman ship and quality is top notch!

anthony tiano
Honestly one of the hardest things I’ve installed

The lack of instructions or decent content is the downfall of this part. Extremely high quality is why you should put up with the lack of instructions. I feel like the small 3/4 piece for the crankcase should’ve been a little more “engineered” for easier firmest and security but other than that good part.