Three-piece lower manifold for a V-style engine intake manifold

摘要

A lower manifold for a V-style internal combustion engine comprising at least three shells: a top shell for mating with an upper manifold; a left shell for mating with a left engine head; and a right shell for mating with a right engine head. The three shells are formed independently by injection molding and are joined as by vibration welding when aligned in a welding jig. The molds for the left and right shells are formed such that the seal ring groove has a rectangular cross-section having sidewalls perpendicular to the lower shell surface because each left and right shell has its own draft angle preferably perpendicular to its lower shell surface. The method and apparatus of the invention permits runner cross-sections to be significantly rounded, which improves air flow characteristics of the runners.