FUEL gets into an engine through the inlet system, is compressed and ignited, the explosion forcing the piston to turn the crankshaft which, in turn, indirectly makes a vehicle move.
What happens, though, after the fuel has exploded? Where do the remnants of the explosion go?
As a piston is forced down by the explosion a valve (or valves) in the cylinder head open to let the spent gases escape, a part of the process called the ‘exhaust stroke'.
The gas is forced from the combustion chamber by the compression stroke and pushed into the exhaust manifold, the main passage between the cylinder head and the exhaust pipe and positioned to align with the engine's exhaust ports.
After exiting the manifold, the gas flows into the exhaust pipe, through at least one muffler (in the case or roadgoing cars), a catalytic converter which helps clean the gas before it is passed into the atmosphere.
The catalytic converter is shaped like a muffler and contains a benign substance such as a platinum or rhodium catalyst which causes a chemical reaction with the exhaust gases passing over them, converting the major pollutants into water, carbon dioxide and nitrogen.
Performance cars are generally fitted with a ‘tuned' exhaust system with individual exhaust pipe lengths calculated to give maximum gas extraction.
The intermittent gas flow through each pipe caused by the opening and closing of the engine's exhaust valves creates a pulse which helps extract the gases from each cylinder as the exhaust valves open in sequence.
Such exhaust systems usually have an exhaust ‘header' in place of the conventional manifold. This header is usually made from welded, rather than cast, pipes which are also of a tuned length.
This type of exhaust system is known as an ‘extractor' exhaust because it is designed to maximise the gas extraction from the engine, giving a free flow of gas through the pipes with minimal back pressure.
(Compiled with the assistance of the Australian Dictionary of Motoring)
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