HKS 65mm Stainless Steel Center Pipe Mid-Pipe | Subaru WRX STI (08-14) (33004-AF002)Increasing the amount of exhaust flow is the first progressive step to increased engine performance and efficiency. The factory exhaust system represents a restriction in the stock configuration. By designing a system that increases the mass and velocity of exhaust flow, it allows for a reduction in backpressure and thermal stress, thus unleashing the engine's potential for increased power, torque, and responsiveness. All HKS exhaust systems are