For Chevy Small Block 2x4-1 Design Stainless Steel Exhaust Header Kit(Polished Chrome) 265-400 V8 T-Bucket 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: 3.4" 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)