The intake manifold is a series if tubes that distribute the air coming into the engine evenly to each of the cylinders, so that the right amount of air can mix with the right amount of gas. Most internal combustion engines run on a four stroke process and during the first stroke air from the intake manifold is sucked into each cylinder through a valve or valves.
The intake manifold major role is to make sure that there is enough air available when the valve opens for each intake stroke and that each cylinder gets the same amount of air as the others. The intake manifold evenly distributes the combustion mixture to each intake port in the cylinder heads.
Intake Manifold Only
Manifolds will be inspected for quality before sending
The intake manifold is the piece on the engine that pulls in the air from the air flow meter and throttle body. Sometimes the throttle body is mounted on it.