An exhaust manifold in a car is usually made of cast iron. It picks up exhaust gases from the cylinders and carries them to the exhaust pipe.
What it Does
Once you turn on the ignition, the air and fuel mixtures will burn. These will give out a few leftovers that would include carbon monoxide and dioxide, phosphorus, sulfur and nitrogen oxides. These gases and compounds are under a lot of pressure as the engine pushes them out and into the exhaust manifold. These gases become very hot and the exhaust manifold collects these gases from various cylinders pushing them into one pipe generally called a collector.
An exhaust gas temperature gauge (EGT gauge) can be used to check the exhaust gas temperature of an engine. It should ideally be used along with an oxygen sensor as the air-fuel ratio that is determined by the EGT gauge is not the only factor that goes into calculating the temperature. The typical temperature would lie between 1250 degrees F and 1600 degrees F. The maximum upper limit for the temperature would be 1800 degrees F. You also need to remember that the reading of the temperature does not imply that the headers or exhaust values are that hot. It means that unless the EGTs are brought down, they will soon be approaching those temperatures. There is no optimal EGT as this changes according to the type and model of engine in the vehicle.