Description: The exhaust manifolds found in the 1978-1991 Buick Chevy Oldsmobile and Pontiac Small Block engine were designed to combine the exhaust gasses from each of the cylinders quickly with a manifold that was cost effective to produce. Our 4-1 Mid-Length off-road headers are designed to allow the exhaust gasses to flow more freely from each 4 cylinder bank and combine in a more efficient manner. Tubing has been optimized for the 5.0L(305ci) and 5.7(350ci) engines. This creates a reduction in cylinder backpressure and improved exhaust gas velocity. These improvements free up lost horsepower and torque. An added benefit is a more performance oriented exhaust sound. 100% brand new, Never been tried or installed Made of High Quality T304 Stainless Steel Material Inlet/ Outlet: 1.50"/ 2.50" O2 Sensor Bung Insertion and Metal Gasket Included 3-Bolt Flange TIG Welded CNC Machine Flange Increase High Flow Air, Instantly Gain 10 -15 Hp. / Tq. No instructions included Professional installation is highly recommended Package including: 1 X Set of Header Exhaust System Gasket(s) and Bolt(s) as shown if Any is Shown in the Picture Above Fitment: 305-350 CID Engine Small Block Please Check Compatibility