An exhaust manifold or header collects the exhaust gases from multiple cylinders into one pipe. Usually constructed of cast iron, the exhaust manifold is a pipe that conducts the exhaust gases from the combustion chambers to the exhaust pipe. It has smooth curves in it for improving the flow of exhaust. The exhaust manifold is bolted to the cylinder head, and has entrances for the air that is injected into it. It is usually located under the intake manifold. A header is a different type of manifold; it is made of separate equal-length tubes.