Automobile engines are complex pieces of machinery with countless moving parts that facilitate combustion, which provides the power by which the vehicle moves. Two important pieces of this puzzle are the intake manifold and the exhaust manifold. The intake manifold is a pipe (or pipes) that supplies a fuel/air mixture to the cylinder where combustion takes place. The exhaust manifold collects exhaust from the cylinders, moves it into one pipe, and sends it toward the exhaust system. Both systems improve the engine's efficiency and power output.
Intake manifolds are usually made of aluminum or cast iron because these materials are resistant to high heat. More recently, composite materials have been used to manufacture intake manifolds. The purpose of the intake manifold is to provide the correct fuel/air mixture to the cylinders, which in turn promotes better engine efficiency and even more power. Because intake manifolds create a vacuum — that is, the air pressure inside the manifold is much lower than that of the earth's atmosphere outside — it can be used to power other elements of the engine or outside units such as the power steering or windshield wiper units.
Exhaust manifolds serve almost the opposite function of intake manifolds. Exhaust manifolds collect exhaust and expel it from the engine by connecting to the exhaust pipe. They are usually made from stainless steel or cast iron for strength and heat resistance, but composite materials can also be used to make exhaust manifolds. Ceramic has been a popular choice, though the ceramic can crack under extremely high temperatures.
Exhaust manifolds are comprised of two parts: headers and collectors. The number of headers depends on the number of cylinders in the engine; one header will connect to one cylinder to collect exhaust, so in an 8-cylinder engine, there will be eight headers. The headers connect to a single pipe called a collector, which funnels the exhaust through the exhaust system. Not all cars will have collectors; this is uncommon, except on performance vehicles like race cars or show cars. Exhaust headers help maximize the efficiency of an engine and can help the engine gain added power.
The most common type of manifold failure occurs when heat in any of the manifolds causes cracking. It is not uncommon to hear of cracked manifolds or cracked headers; when this happens the only option for repair is to replace the damaged part, which can be a costly and time-consuming repair.