For 67-81 Chevy Small Block F-Body SBC 265-400 4-1 Design Stainless Steel Clipster Exhaust Header/Manifold Made of high quality steel with 2 x 4-1 direct bolt-on design TIG welded CNC machine flange Metal gasket included / Inlet: 1.8"x1.5" (Oval) / Outlet: 2.85" (ID), 3" (OD) /Two 2.125"outlet reducer 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)