Exhaust manifolds are required to comply with the legal regulations of emissions legislation. With the exhaust system fitted, the S54 engine complies with the exhaust emission regulations EU4 (valid for Europe) and LEV1 and LEV2 (valid for US version). During the combustion of fuel, the oxygen in the air leads to the creation of water and carbon dioxide. As the combustion is not quite complete, other combustion products arise. These constituent elements of the emissions have a proportion of 1 %. In petrol engines, it is mainly carbon monoxide, hydrogen chlorides and nitrogen oxides that are created. The catalytic converter helps to convert these pollutants into water and carbon dioxide.
In the catalytic converter of the S54 engine, metal monoliths are used; these have several thousand channels through which the exhaust gas flows. The advantages compared to ceramic monoliths (ceramic catalytic converters) are lower exhaust-gas back-pressure and a shorter warming phase.
Chemical reactions with impurities, for example an excessive amount of lead in the fuel, can destroy the catalytic layer (chemical poisoning). Chemical poisoning also arises in the case of very high amounts of oil in the emissions. The active catalytic layer can also be covered by lead and sulphur additives from fuel and oil (mechanical poisoning). In addition, there is the probability of thermal ageing. A rising number of combustion misfires that occur sporadically can be an indication of a thermally destroyed catalytic converter.