For Mazda Miata MX-5 4-2-1 Design Tri-Y Stainless Steel Exhaust Header Kit - NA 1.8L 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: 2.25"x1.5" / Outlet: 2.25" 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)