The stock header is the most restrictive part of the exhaust on the K20A engine. We have been spending years of effort to develop a header with longer 4-2 conjunction to obtimize torque and hp across the power band. Finally we have come up with a 45mm piping size for primaries with 65mm pipe for collector. The 4-2-1 design with the special “Power Neck” is to improve exhaust efficiency other than increasing volume. All exhaust tubings are 1.2mm thick to reduce as much weight as possible while maintaining a strong enough structural design to with hold the heat and stress caused by the engine. The header replaces the stock 4-1 portion and the stock catalytic converter. This header was developed and intended for race and track use only. Dyno tested 15+whp gain. Requires JDM front swaybar for fitment.