For Honda Prelude 4-2-1 Tri-Y Design Stainless Steel Exhaust Header Kit (Polished Chrome) H22 BA Made of high quality steel with 4-2-1 direct bolt-on design TIG welded CNC machine flange O2 sensor bung insertion / Metal gasket included / Inlet: 1.8"x1.5" (Oval) / 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)