HKS Exhaust Manifold - Equal Length Header - With Cat - GT86 & BRZHKS Super Manifold with Catalyser GT SPEC for GT86 & BRZ 42. 7 > 50. 8 > 60mm pipe diameter Manufactured from SUS 304 Stainless Steel The HKS 4 2 1 manifold is equal length and has a HKS Catalyser which has less resistance and has passed Japanese exhaust gas regulations. The manifold produces more power in the torque dip area, and top end power is improved. Fensport Tip: For the best result, Ecu will require tuning, we recommend our GT86 & BRZ NA