For Chevy Tri-Five 2x4-1 Design Stainless Steel Exhaust Header Kit (Polished Chrome) Made of high quality steel with 2 x 4-1 direct bolt-on design TIG welded CNC machine flange Metal gasket included / Inlet: 1.5" / Outlet: 2.5" 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)