Purpose of Exhaust Manifold

by Matthew Lee
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Motorcycle Exhaust image by Billy Tait from Fotolia.com

In an internal combustion engine, the exhaust manifold collects the products of combustion (exhaust gases) from two or more cylinders and conducts these to a single exhaust pipe.


Typically made of stainless steel, cast-iron or heavy-gauge steel, the exhaust manifold directs exhaust gases from multiple cylinders to a single exhaust pipe. In so doing, the exhaust manifold also helps to minimize leakage of heat, air and gases. Copper gaskets connecting the manifold to the cylinder heads can be used to create a more airtight system, though these are not necessary.


By minimizing the loss of heat, the exhaust manifold reduces the temperature under the hood. This helps to prevent overheating and damage to heat-sensitive parts while increasing power by reducing the temperature of the intake manifold. As gases move more quickly in higher temperatures, the exhaust manifold helps to increase the speed at which exhaust leaves the system.


As cylinders fire at different times, an ideal exhaust manifold would contain pipes of different lengths to ensure that exhaust gases from one cylinder have been cleared from the system before another fires (i.e., to prevent back pressure). Due to space limitations, however, exhaust manifolds typically contain short pipes of uniform length. Though compact, this design increases back pressure, subsequently increasing heat loss under the hood and reducing engine performance.

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