Kooks Custom Headers - 2011 Mustang GT - 5.0L 4V Complete Headers and Exhaust 2011 Ford Mustang 5.0L Headers and Complete Exhaust System. Headers are 1 3/4" x 3" with a 3" High Flow Catalyst Equipped X-Pipe and a Kooks Racing 3" Cat-Back Exhaust that includes Mandrel bent 3" Over the Axle Tubing. Entire System is made in Aircraft Quality 304 Grade Stainless Steel Material!