The Subaru boxer platform can have issues with oil surging in the heads. It can be related to the level of performance, driving style, track conditions and so on. This burden is often overwhelming to the PCV's A/O separator or Catch Can system causing them to fill. Filling an A/O separator or catch can causes oil levels to drop increasing the potential for oil starvation. Another condition is if a catch can fills, and overflows onto a hot engine and/or exhaust system creating a fire potential, which has been known you happen. The Oil Control Valve prevents oil flow out of the valve cover ports based on the lateral forces placed on the car. This design has been successfully used in aerobatic aircraft for years and we have adapted the design to be suitable for lateral loading vs inverted flight (which rarely happens in cars). Under straight line acceleration, braking and moderate cornering the PCV vents work just as they normally would; letting blow-by gasses vent from all ports. Under severe lateral loads the port from the surging head (facing the outside of a corner) is closed, not allowing oil to pass into the A/O or catch can setup. The balance ports and remaining head and crankcase ports still operate as normal. This has no negative effect on the engine or engine performance, while assuring blow-by gasses ONLY are permitted through the PCVs ports. *Attention!* This is not a product that would EVER be needed on a street car. It is a product for racecars, specifically boxer engine cars, able sustain +1.5Gs consistently. If you are unsure if you have a 'racecar' ask yourself some simple questions. Does my car have a true safety cage? Does my car run race slicks? Do I have a competition license? If you do not answer yes to all 3, this product would very likely be utterly useless for you.