An inertia charge intake manifold is associated with an internal combustion engine having a plurality of cylinders. The intake manifold includes a plurality of elongated separate branch pipes each corresponding to a respective one of the cylinders. The intake manifold also includes a common flange for connecting a first end of each branch pipe to the internal combustion engine. The common flange has a first surface attached to the internal combustion engine. Further, the intake manifold includes a surge tank to which a second end of each branch pipe is connected. The common flange, the surge tank and each branch pipe are made of a hard thermoplastic synthetic resin. The common flange is integrally connected to the surge tank.