The Radium Engineering Top Feed Upgrade Fuel Rails for Subaru EJ22/EJ251 are designed for naturally aspirated Subaru EJ applications that came factory-equipped with top-feed injectors. Rather than converting the intake manifold to a completely different injector layout, this kit upgrades the rails themselves with higher-flow aluminum rails, 8AN ORB plumbing options, and improved support for performance fuel-system components.

Each rail features three 8AN ORB ports, giving the system six total connection points for feed, return, regulator, pressure sensor, gauge, or pulse-damper configurations. Radium also includes thermal-insulating spacers to help reduce heat transfer from the intake manifold into the fuel rails. A Radium 20-0776 fuel pulse damper can be installed in the center port, and the factory-style fuel pressure regulator can be retained with Radium adapter 20-0303 when required.

Injector requirements depend on the engine. EJ251 applications can retain the OEM air-assist injectors, while EJ22 applications cannot use the factory air-assist injectors because their 11mm upper O-rings do not match the rails 14mm injector ports. Aftermarket injectors must use 14mm upper and lower O-rings, and Radium specifies compatibility with Bosch EV14-style injectors. California-spec EJ22 applications also require additional injector seats, spacers, and mounting hardware to eliminate the factory air-assist system.