Gibson Performance GP400S Performance Header. Performance Header; Stainless Steel; 1.5 in. Heavy Duty 409L Stainless 16 Gauge Tubing. Thick Laser Cut Port Flanges. Every exhaust system is designed for hassle free, bolt on installation with professional looking results. Gibson's exhaust systems are engineered & dyno-tested to decrease backpressure, and produce more torque, with increased horsepower and better fuel economy. Processing begins as soon as an order has been placed, therefore we cannot change, cancel or modify orders once they have been confirmed.