For Subaru Impreza WRX GD GG Stainless Steel 2-PC Header Exhaust Manifold+Downpipe Made of High Quality Stainless Steel Material TIG Welded CNC Machine Flange Increase High Flow Air and Maximize Performance; Instant Gain 10 to 15 Hp. / Tq. Header - O2 sensor bung insertion / Metal gasket included / Inlet: 1.5" / Outlet: 2" Downpipe - Inlet Size: 4.375" x 2.25" (Oval) / Outlet Size: 3" / Piping Diameter: 3"