Exhaust system

An exhaust system conveys burnt gases from an internal combustion engine and typically includes a collection of exhaust pipes. In the most basic sense, the exhaust system simply vents waste gases from the engine. Depending on the overall system design, the exhaust gas may flow through a turbocharger to increase engine power, a catalytic converter to reduce air pollution, and a muffler to reduce noise.



Terminology


Manifold or header

In most production engines, the manifold is an assembly designed to collect the exhaust gas from multiple cylinders and combine those flows into a single pipe. Manifolds are often made of cast iron in stock production cars, and may incorporate material saving design techniques. Most production manifold designs are manufactured to use the least amount of metal, to occupy the least space necessary, or have the lowest production cost. These design restrictions often result in a design that is cost effective but that does not do the most efficient job of venting the gases from the engine. Inefficiencies generally occur due to the nature of combustion engines and their multiple cylinder banks. Since cylinders fire at different times, exhaust leaves them at different times. This time difference can create pressure waves when gases emerging from one cylinder are not completely vacated through the exhaust system by the time another does. This creates a back pressure and restriction in the engine's exhaust system that can restrict the engine's true performance possibilities.

A header is another name for a manifold, but which specifically refers to an enhanced manifold that has been designed for performance. During design, engineers will create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. This design results in a header that is more efficient at scavenging the exhaust from the cylinders. Headers are generally circular steel tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to the common outlet all of equal length, and joined at narrow angles to encourage pressure waves to flow through the outlet, and not back in the direction of the other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine RPM range.

Headers are generally manufactured by aftermarket automotive companies, but sometimes can be purchased from the high performance parts department at car dealerships. Generally, most car performance enthusiasts purchase aftermarket headers made by companies solely focused on producing reliable, cost effective, and well designed headers specifically for their car. Headers can also be custom designed by a custom shop. Due to the advanced materials that some aftermarket headers are made of, this can occasionally cost a lot of money. Luckily, exhaust is one system of a car that can be custom built for any auto, and generally non-specific to the motor or design of your car. The only requirement for producing a performance exhaust system is designing a header that properly makes a solid connection to the engine. This is usually accomplished by correct sizing in the design stage, and the selection of a proper gasket type and size for the engine.

Headers are also called extractors in Australia.


Header-back

Header-back (or header back) refers to the portion of the exhaust system from the outlet of the header to the final vent to open air— everything from the header back. Header-back systems are generally produced as aftermarket performance systems for cars without turbochargers.


Turbo-back

Turbo-back (or turbo back) refers to the portion of the exhaust system from the outlet of a turbocharger to the final vent to open air. Turbo-back systems are generally produced as aftermarket performance systems for cars with turbochargers. Some turbo-back (and header-back) systems replace stock catalytic converters with others having less flow restriction. Some systems eliminate the catalytic converter (sometimes called catless or no kitty), which may or may not be legal depending on geographic location and whether the car will be driven on public roads.


Cat-back

Cat-back (also cat back and catback, and more recently axle back) refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. This generally includes the pipe from the converter to the muffler, the muffler itself, and the final length of pipe to open air.

Cat-back exhaust systems are a very popular aftermarket performance enhancement. They generally use larger diameter pipe than the stock system. Good systems will have mandrel-bent turns that allow the exhaust gas to exit with as little back pressure as possible. The mufflers included in these kits are often glasspacks, again to reduce back pressure. If the system is engineered more for show than functionality, it may be tuned to enhance the lower sounds that are lacking from high-RPM low-displacement engines.


Tip

The end of the final length of exhaust pipe where it vents to open air, generally the only visible part, often ends with just a straight or angled cut, but may include a fancy tip. The tip is usually chromed, and is often of larger pipe than the rest of the exhaust system. This produces a final reduction in pressure, as well as prevents rusting of the tips, and can be used to enhance the appearance of the car. These are the least expensive parts of the system.