Intake Manifold

An intake manifold is an engine component which bolts to an engine's cylinder head. It is the place where outside air and fuel (gasoline) mix before going into the combustion chamber. An intake manifold contains "runners" (hollow chambers) which connect to each combustion chamber.

Operation
When an engine operates, outside air is sucked into the intake manifold. As it enters, a small amount of gasoline, either from a carburetor or fuel injection system, is sprayed into the air stream where it mixes with the air. Much of the fuel is in the form of fine droplets at this point. The air/fuel mixture gets carried into a the intake manifold's runner which leads toward the combustion chamber. Inside the runner, a vacuum is present which allows the fine droplets of gasoline to "boil" and turn to vapor (think back to high school experiments). A better air/fuel mix (in terms of combustion) is the result. The air/fuel mix then enters the combustion chamber.

In addition, most intake manifolds contain other passages as well. Some passages are for coolant flow which help channeled coolant throughout the cylinder heads and heater core and keep the engine for overheating. Other passages serve emission purposes. Channels in the intake manifold recirculate a small amount of hot exhaust gasses back into the combustion chamber to reduce combustion temperatures.

Location
Intake manifolds are usually positioned on the top of "V-shaped" motors like V6's and V8's and to the side of "inline" motors such as most 4 cylinder and "straight 6" motors. An intake manifold may be one or two piece. The engine's carburetor or fuel injection system mounts to the intake manifold along with the air filter canister.

Possible problems
Older engines utilized cast iron manifolds that were stout yet heavy. Newer vehicles use aluminum allow manifolds which reduce weight but are more prone to intake gasket leakage problems. The differing expansion/contraction characteristics between cast iron and aluminum often cause gaskets to fail after several years. The result is coolant or vacuum leaks. See replacing an intake manifold gasket.