Intake manifold for multicylinder internal combustion engine

Abstract

An intake manifold for a multicylinder internal combustion engine having fuel supplying means such as a fuel injection device or a carburetor includes a branch intake conduits each communicating with one of the cylinders of the engine, an extension tube connected to a primary suction conduit of the carburetor, and an incoming fuel charge heating device mounted on the bottom of the intake manifold. The extension tube has a curved portion in its wall directed toward a part of the surface of the bottom of the intake manifold at which the axial center lines of the branch intake conduits gather together and cut to form an open end of the extension tube. The incoming fuel charge heating device has a heating surface disposed near the open end of the extension tube, which is smoothly curved toward the bottom of the intake manifold. The open end of the extension tube is disposed on a plane forming an acute angle with the wall of the tube at the outermost edge of the open end and contiguous at the innermost edge thereof with a straight portion of the wall of the tube, as viewed in cross section. The incoming fuel charge heating device may include positive-temperature-coefficient thermistors.