An intake manifold is a system of passages which manner the fuel mixture from the carburetor to the intake valves of the steam engine. Manifold design has much to do with the competent process of an engine. For smooth and even process, the fuel charge taken into each cylinder must be of the same strength and quality. Distribution of the fuel ought to, therefore, be as even as possible. This depends really upon the design of the intake manifold. Dry fuel steam is an ideal form of fuel charge, but present-day fuel prevents this unless the combination is subjected to high temperature.

If the fuel charge is heated too highly, the power of the steam engine is condensed because the heat expands the fuel charge. Therefore, it is better to have some of the fuel deposited on the walls of the cylinders and various vents. Manifolds in modern engines are designed so that the amount of fuel condensing on the intake various walls is reduced to a minimum. In a V-8 engine, the intake multiple is mounted between the cylinder heads. The L-head engine's manifold is bolted to the surface of the block, and the I-head manifold is bolted to the tube head.