For Buick/Chevy / Oldsmobile/Pontiac Small Block 4-1 Design Stainless Steel Exhaust Header Made of High Quality T304 Stainless Steel for Strength & Durability TIG Welded CNC Machine Flange for Percision & Fitment Offers the Best Flow Characteristics for the Engine at High Engine Speeds Increase High Flow Air, Instantly Gain 10 -15 Hp. / Tq. 1.5" Inlet / 2.5" Outlet / O2 Sensor Bung Insertion & Gasket Included