DNA Motoring HDS-HC88-BK 4-2-1 Exhaust Header for Honda D-Series 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: 1.75" / Outlet: 2" Increase high flow air, instantly gain 10 to 15 Hp. / Tq Professional Installer is Highly Recommended No Instruction Included