Reverse Rotation Intake Manifold

The AMS Performance Reverse Rotation Intake Manifold is engineered to deliver exceptional performance for Subaru EJ20 and EJ25 engines, aiming to surpass the competition in power output. It features a durable cast design with precision-crafted interior geometry for maximum efficiency and airflow, utilizing Solidworks© and CFD software for its 4.5L plenum design. The manifold boasts CNC machined bellhorns acting as internal velocity stacks and massive 2.5″ tapered runners with 13” lengths to optimize airflow and high RPM horsepower capabilities. This intake manifold is designed for aftermarket top-feed injectors with a 48mm overall length and 11mm inlet. Standard Subaru-style injectors, including side feeds and stock STI injectors, cannot be used. It is not compatible with side feed to top feed conversion rails and requires aftermarket fuel rails and lines; it will not fit with stock components. Furthermore, it is not compatible with top-mount intercoolers and will require custom bracketry to mount the factory upper coolant reservoir. The bottom of the plenum includes four 1/8″ and one 1/4″ NPT ports for vacuum accessories. Installation of the reversed configuration requires the relocation of the alternator and removal of the A/C compressor, necessitating custom intercooler piping. Mild custom fabrication for intercooler piping may also be needed with the standard configuration due to throttle body placement. For 2008+ STI models, mild clearancing of the A/C compressor line might be necessary. The throttle body opening accepts larger throttle bodies up to 2.625” (66.675mm), or 70mm with minor porting, though adapter flanges may be required. The manifold is flanged for 04+ STI drive-by-wire throttle bodies, but cable throttle bodies can be used with custom fitting and an adapter flange. Some port matching may be required when used with CNC or hand-ported cylinder heads.