If you want to go even further to reduce exhaust restriction and gain power, then consider installing headers . Headers replace the factory exhaust manifolds, which usually flow poorly. An exhaust header has individual tubes for each exhaust port, allowing each exhaust pulse to flow unobstructed from the cylinder head. All tubes meet in a larger tube called a collector. The tubes on headers are usually larger in diameter than the runners on an exhaust manifold and the tubes are mandrel bent for gradual radius bends, which reduces restriction and increases exhaust flow.