The bolt on APS Tumbler Valve Delete Housing is a precision machined aluminium housing that replaces the stock Subaru component (which mounts between the cylinder head and the intake manifold/throttle body assembly) - and dramatically reduces the restriction between the throttle body and the inlet valves at high horsepower levels. Also included in the APS Tumbler Delete system are two precision manufactured Throttle Position/Servo couplings. These components are mandatory for continued correct operation of the tumble control drive/feedback system. Without these components, the engine management system will detect a tumbler valve malfunction. With plenty of room to grow your fuel system, this innovative component not only houses the stock WRX or STI injectors, but also has provision for 4 auxiliary Bosch style injectors for high horsepower applications. Thus providing the WRX performance enthusiast with the best possible drivability offered by the stock injectors and allows for the additional auxiliary injectors to be utilized only when needed at high power levels. The auxiliary injectors can be mapped by most aftermarket engine management systems across the entire RPM range.