For Chevy/GMC C/K-Series Small Block V8 2pcs Stainless Steel Header/Exhaust Manifold (Polished) Made of High Quality T-304 Stainless Steel with Computerized Mandrel-Bends for Strength and Durability i.e. Maximizing Smoothest High Exhaust Air Flow Rate 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: 1.25"(OD) / Outlet: 3"(OD) / 10mm Thick Header Flange / 16 Gauge Wall Piping / Metal Gaskets Included