Made of High Quality T-304 Stainless Steel Material Metal Gasket Included ; 2 X 4-1 Racing Design 1-3/4" OD Primaries ; 3" Collector ; 3"-2-1/2" Collector Reducer Flanges Increase high flow air, instantly gain 10 to 15 Hp. / Tq. Full Length Headers for Higher Horsepower