For Chevy Big Block Hugger V8 4-1 Design 2-PC Stainless Steel Exhaust Header - 396 402 428 454 Made of high quality steel with 2-pieces 4-1 direct bolt-on design TIG welded CNC machine flange Metal gasket included / Inlet: 1.75" / Outlet: 2.5" Increase high flow air, instantly gain 10 to 15 Hp. / Tq Application: Please check part finder on top of the page (Professional Installer is Highly Recommended) (No Instruction Included)