Exhaust Manifold vs. Intake Manifold

The automobile exhaust manifold and the intake manifold are different engine components, although the auto novice often mistakenly sees them as the same. To complicate things, the intake manifold and the exhaust manifold both process automobile fuel or gases. One (the intake manifold) processes raw fuel, the other (the exhaust manifold) processes burnt fuel. If you are interested in knowing more about the automobile gasoline combustion engine, it will help you to have a good understanding of these two manifolds and what they contribute to the engine's operation. The information below will help you with this understanding.

Intake Manifold Construction

In some automobiles the engine's intake manifold is manufactured of aluminum or cast iron. The reason is that both of these metals resist heat without warping or melting. Some newer cars now use intake manifolds made of composite plastic materials.

Exhaust Manifold Construction

Some exhaust manifolds, like intake manifolds, are constructed of cast iron. Others are made from stainless steel, and still others are made from ceramic which does not have the durability of steel and is more likely to crack. The exhaust manifold process conducts away hot gases produced by the exploding fuel-air mixture while the intake manifold introduces a cooler, unburned air-fuel mixture.

Intake Manifold Function

Purposes of the intake manifold are threefold. It distributes the fuel-air mixture into intake ports of the engine's cylinder heads, acts as a solid mount for fuel injectors, carburetor, and other engine components, and is one of the components of a vacuum system that creates power for power assisted brakes, emission control, cruise control, ignition advance. When the engine begins its intake stroke, the piston moves downward creating a vacuum which pulls the fuel-air mixture into the cylinder. The piston then moves upward, compressing the air-fuel mixture until a spark ignites the mixture. The resulting explosion then drives the piston down again starting a new cycle.

Exhaust Manifold Function

The exhaust manifold directs exhaust gas away from the engine's cylinders. It acts as part of a pipeline through which the noise of the explosion of the fuel-air mixture is reduced by the exhaust system's muffler, and it pushes the hot gas out into the open air through the system's exhaust pipe. For some automobiles, another component referred to as exhaust headers—or extractors—when added into this system, increases engine efficiency. These extractors, by converging into a central tube (the Collector) act as a sort of vacuum that pulls the burnt fuel gas more quickly out of the engine's cylinders and thus decreases back pressure that reduces engine power.

How the Exhaust System Works

After its downward stroke, and after the fuel-air mixture explodes, the piston moves upward again, forcing the hot, burned gas out of the cylinder and into the open air.