A stock automobile usually comes with a manifold which receives the hot exhaust gas flow from the engine and then routes them into a pipe which then carries them to the rest of the system. Unfortunately though it was designed to be inexpensive to make and fairly easy to install on the assembly line, it has a major drawback in that it creates back pressure.

Back pressure means that the gas flow hits some type of resistance which forces some of the gas back into the engine. Now some of the power of the engine is diverted to forcing the exhaust gases to past the restrictions. The net result is less power to the ground.

A different approach is using a device called a header. This is a design that uses individual pipes for each exhaust port. The typical after market header pipes have much smoother bends which means it decreases airflow resistance. Next the header pipes then combine together at an at something called an exhaust collector and then on to another pipe which then feeds the gas flow to the catalytic converter.

When these pipes have been "tuned" in by changes in their length a special system  is created so that when gas passes down one tube and then through the common pipe, (sometimes referred to as a down header pipe), it creates a slight vacuum in another pipe. This then tends to suck the hot gas from the second pipe through the system. This further reduces back pressure.

Using this approach an after market system can be even more tuned to perform better or offer the least restrictions at particular RPM ranges. This means that these systems are normally  designed for a particular application of where you want the maximum power.

Since colder air is denser than hotter air, and weighs more it is harder to push or suck through an exit system. So you want to keep the exit gases hot for a while. This is the reasons why some  systems are ceramic coated which reduces the heat being radiated in the engine compartment, and this helps to increase the temperature in the exit pipes.

This also results in an increase in the velocity of the gases. In place of ceramic coatings there are some types of special high heat paints which are less expensive are available for your system. A third choice to retain heat when you wrap each individual pipe in some special tape which helps the pipe retain internal heat.

When you add a header to your car you can get certain benefits including:

•     The engine sound is changed to a more pleasing sound;
•     Miles per gallon may be increased ;
•     Should give you an  increase in peak engine power;
•     And if made out out stainless steel , which last much longer.

However, nothing is free, and there can be some disadvantages along with their benefits. The typical increase in sound from a header may annoy other people or lead to vehicle noise infractions and tickets from the local police department. Some system designs  decrease the automobile's ground clearance and thus can be damaged or dragged off of the car. Because of the tuning effect some systems can also lower your torque at low engine rpm's.