For Ford Mustang GT High-Performance 2x4-1 Stainless Steel Exhaust Header Kit 4.6L V8 Made of high quality steel with 2-pieces 4-1 direct bolt-on design TIG welded CNC machine flange O2 sensor bung insertion / Metal gasket included / Inlet: 1.67" / Outlet: 2.39" Increase high flow air, instantly gain 10 to 15 Hp. / Tq Application: Please check part finder on top of the page (Professional Installer is Highly Recommended) (No Instruction Included)