High-powered modified Subaru engines tend to generate excessive blow-by oil and gasses. In these cases, an ordinary small catch can may quickly fill with oil and not be adequate. Like the Radium Engineering Subaru Dual Catch Can Kit, the AOS (Air Oil Separator) kit is responsible for keeping blow-by oil and other pollutants out of the intake pipe, manifold, turbocharger, and intercooler during all engine loads. The main difference is that an AOS-"R" system "returns" what is collected back into the oil pan so there is no servicing required. The built-in heater keeps water from condensing in the AOS. And because water is more dense than oil, there is an integrated water trap found around the bottom perimeter of the can.

This prevents water from descending into the oil pan if ever present. Furthermore, because the water is trapped against the heater, it will eventually boil and evaporate out of the system. The AOS is constructed of three CNC machined sections that screw together and are sealed with O-rings.

20-0607 
09-13 Subaru Forester XT
08-14 Subaru Impreza WRX
08-14 Subaru Impreza WRX STi
15-21 Subaru WRX STi

Dimensions
AOS Height: 6.3" (without fittings)
AOS Diameter: 3.45" Round 
AOS Capacity: 20.3 oz (600mL)

Ports
Inlet: 7/8"-14 threaded for 10AN ORB fittings
Outlet: 7/8"-14 threaded for 10AN ORB fittings
Return: 7/8"-14 threaded for 10AN ORB fittings
Coolant: 7/16"-20 threaded for 4AN ORB fittings (x2)

Included
-Machined alumium Radium Engineering Air Oil Separator
-Subaru specifically designed mounting bracket
-All necessary SAE J30R7 rated PCV/Emissions hose
-Coolant hoses and fittings
-All necessary aluminum fittings and hose-ends
-Stainless steel mounting hardware 

Designed for LHD vehicles, some adaption is required for RHD vehicles