In order to reduce the weight of an engine, aluminum has been increasingly used as a material for the intake manifold --an engine component formerly made of a heavier metallic material. Recently, with the aim of further reducing the engine weight, more and more intake manifolds are being made of plastics. To bring the plastic manifold into practical use, a number of methods have been proposed and put into practice; these methods include melt core molding, injection molding and blow molding.Formerly, the melt core molding process had to be used to obtain a solid plastic intake manifold port section having a large curvature. The newly developed intake manifold does not need that process to form its solid port section having a large curvature. Instead, it employs a new process for solid injection molding in which the core is drawn out while it is rotated. This has made it possible to improve the smoothness of the port interior surface and reduce the weight and cost of the intake manifold.In this paper we discuss studies of plastic materials, and summarize result of our analysis of molding methods using CAE technology. We also report on the results of our study of the newly-developed product, focusing primarily on vibration noise and engine performance.