Abstract: An exhaust header system for an internal combustion engine having improved exhaust gas flow characteristics. Primary pipes extend from openings in a flange bolted to the engines exhaust ports. The primary pipes come together at a collector pipe into which the primary pipes extend slightly. The ends of the primary pipes are substantially parallel, uniformly spaced around the collector pipe axis and have end surfaces lying substantially in a single plane. A generally pyramidal transition piece has a base corresponding to, and secured to, the primary pile end surfaces so as to cover the area between the pipe ends. The pyramid apex extends along the collector pipe centerline toward the exit end. The length and cross section of the transition piece is selected to provide a smooth transition from the greater combined internal cross section of the primary pipe ends to the lesser cross section of the collector pipe exit end.