For Cadillac Big Block BBC V8 425/472/500 Stainless Steel 4-1 Exhaust Header Manifold Made of High Quality T-304 Stainless Steel Material 2 x 4-1 High Performance Racing Spec. Design, Produces the Most Top End Power Offers the Best Flow Characteristics for the Engine at High Engine Speeds Increase High Flow Air, Instantly Gain 10 -15 Hp. / Tq. Inlet: 1.65" / Outlet: 2.85" / Metal Gasket Included