Engine noise barrier

A co-injection molded air intake manifold shell comprises an inner and outer skin layer separated by a sound absorbing or sound insulation core. Each skin layer is composed of a polyamide resin which, optionally, contains glass fiber reinforcement and high specific gravity fillers such as barium sulfate or tungsten. The sound insulating core is composed of a high density material having a foam structure, such as a polyamide resin. Skin layers are provided with a plurality of pockets to permit distribution of localized lumped masses at predetermined locations tailored to increase noise transmission losses. A single layer air intake manifold shell having non-uniform thickness is also provided. The thickness of the single layer air intake manifold shell is larger over preselected noise sources of larger amplitude to maximize noise attenuation for a nominal air intake manifold shell thickness.