Precision Works AOS Air Oil Separator - Subaru WRX 02-14 STI 04-21Precision Works AOS Air Oil Separator Subaru WRX 02 07 STi 04 19 Air oil separator removes oil from engine ventilation system so the oil does not get into the intake system. Key Features: Retains OEM PCV valve Engine performs cleaner & efficiently Precision CNC machined 6061 billet aluminum High quality continental hose Includes fittings, caps, and zip ties Designed to work with the following Subaru: Subaru WRX 2002 2007 Subaru STI 2004 2021 Subaru