Manifold or header

Manifold or header

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 using the least metal, to occupy the least space necessary, or having 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 back pressure and restriction in the engine's exhaust system that can restrict the engine's true performance possibilities.

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.[4] 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 headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine revolutions per minute range.

A common method of increasing the power output of an engine is the use of upgraded headers.[5] The increased power output is often due to a result of a larger cross-section area of the pipes (reducing the resistance on the exhaust gasses) and/or designing the pipe lengths so that the pressure wave assists in exhaust scavenging. For inline-four engines and V8 engines, exhaust manifolds are usually either a 4-2-1 design (where the four pipes merge into two, followed by a separate merge of these two pipes into one) or a 4-1 design (where the four pipes directly merge into one).

Headers are generally made by aftermarket automotive companies, but sometimes can be bought from the high-performance parts department at car dealerships. Generally, most car performance enthusiasts buy aftermarket headers made by companies solely focused on producing reliable, cost-effective well-designed headers specifically for their cars. 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.