An exhaust pipe must be carefully designed to carry toxic and noxious gases away from the users of the machine. Indoor generator and furnaces can quickly fill an enclosed space with poisonous exhaust gases such as hydrocarbon, carbon monoxide and nitrogen oxides, if they are not properly vented to the outdoors. Also, the gases from most types of machines are very hot; the pipe must be heat-resistant, and it must not pass through or near anything that can burn or can be damaged by heat. A chimney serves as an exhaust pipe in a stationary structure. For the internal combustion engine it is important to have the exhaust system "tuned" for optimal efficiency. Also this should meet the regulation norms maintained in each country. In China, China 5; In European countries, EURO 5.
In most production engines, the manifold is an assembly designed to collect the exhaust gas from two or more cylinders into one pipe. Manifolds are often made of cast iron in stock production cars , and may have material-saving design features such as to use the least 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 the combustion engine and its cylinders. Since cylinders fire at different times, exhaust leaves them at different times, and pressure waves from gas emerging from one cylinder might not be completely vacated through the exhaust system when another comes. This creates a back pressure and restriction in the engine's exhaust system that can restrict the engine's true performance possibilities. In Australia, the pipe of the exhaust system which attaches to the exhaust manifold is called the 'engine pipe' and the pipe emitting gases to ambient air called the 'tail pipe'. Regardless of the negative attributes focused upon by potential sellers of steel tube exhaust outlet configurations, engineers who design engine components choose conventional cast iron exhaust manifolds can similarly list positive attributes, such as an array of heat management properties and superior longevity than any other type of exhaust outlet design. For the average consumer, having trouble with an exhaust outlet system may qualify as 'poorer performance'.
A header is a manifold specifically designed for performance. During design, engineers 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 equal length , and joined at narrow angles to encourage pressure waves to flow through the outlet, and not back towards other cylinders. In a set of tuned headersthe pipe lengths are carefully calculated to enhance exhaust flow in a particular engine revolution per minuet range.
Headers are generally made by aftermarket automotive companies, but sometimes can be bought from the high-performance parts department at car dealership. Generally, most car performance enthusiasts buy aftermarket headers made by companies solely focused on producing reliable, cost-effective 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 be expensive. Luckily, an exhaust system can be custom built for any car, and generally is not specific to the car's motor or design except for needing to properly connect solidly to the engine. This is usually accomplished by correct sizing in the design stage, and selecting a proper gasket type and size for the engine