NOT CARB-APPROVED. ILLEGAL TO USE OR INSTALL IN CALIFORNIA. IF YOU LIVE IN CA, WE CANNOT SHIP YOU THIS ITEM

• SUBARU IMPREZA WRX STI 4D EJ257 2004 - 2007

Reduced pressure with Bypass Pipe (Racing Header)

When strong vacuum is created, to the contrary, there also is strong pressure. Cylinder pipes are connected with Bypass Pipe to reduce pressure as minimum as possible. Rhythm of "Pressure" and "Vacuum" inside manifold is controlled. Besides, number of bypass pipe and positions are designed to optimize for each engine characteristics. It enables to reduce pressure without change of vacuum. Therefore, there is no drop of torque. The engine will have Inertia Exhaust Gas Efficiency (Efficiency to increase horsepower of NA engine) and flat torque characteristics, which enables easy drivability.

Advantage of 4-2-1 Straight Junction (Super Header)

HKS selected 4-2-1 junction design that has best result for street use from study of various data about a lot of engine characteristics and exhaust gas pulse. 4-1 Junction type has shorter length to the junction part and it is better for competition purpose that require performance only at high rpm range. But it has too less torque at low rpm range for street driving. HKS' Straight Junction Design accelerates exhaust gas with exhaust gas pressure and it pulls out combustion gas. Exhaust gas efficiency is improved with the design.

Turbine performance is affected by Exhaust Manifold.

Shape, diameter of pipes and production quality of exhaust manifold between engine and turbine affect performance of turbine. HKS Exhaust Manifolds were developed with know-how and data from long time development experience of turbo technologies. Diameter of pipes and design of bending are designed for each engine performance and displacement. Welding portion between flange and pipe is flattened to reduce friction of exhaust gas. As a result, response of turbocharger at middle and high rpm range is improved. Both torque and horsepower are also increased.