For Chevy Gen 2 Mark IV Big Block V8 2 x 4-1 Stainless Steel Shorty Exhaust Header w/Circle Port Made of High Quality Stainless Steel TIG Welded CNC Machine Flange 2 x 4-1 Racing Design Increase High Flow Air, Instantly Gain 10 to 15 Hp. / Tq Main Collector Piping Diameter: 2.58" / Inlet: 1.65" (8 Circle Ports) / Outlet: 2.85"