For Mini Cooper R50/R53 1.6L Stainless Steel 4-1 Header Exhaust Manifold Made of High Quality T304 Stainless Steel Material / TIG Welded CNC Machine Flange Offers the Best Flow Characteristics for the Engine at High Engine Speeds Increase High Flow Air, Instantly Gain 10 -15 Hp. / Tq. 4-1 Design / O2 Sensor Bung Insertion and Metal Gasket Included Inlet: 1.5" / Outlet: 2.25" / Piping Diameters: 4 X 1.5" Manifold Piping; into 1 x 2.25" Major Pipe