The introduction of more stringent exhaust emission standards in Europe and in the USA demands substantially more effective exhaust gas treatment than previous standards have prescribed. In SI engines, the cold-start phase is responsible for contributing by far the largest proportion of total emissions. To start the chemical reaction, catalytic converters require a minimum temperature which, at present, cannot be reached quickly enough by the engine exhaust gas. The use of close-coupled main catalytic converters, accurately matched to the engine, offers the potential necessary to achieve compliance with European emission standards. A description of the design procedure and the installation of the series design is provided here followed by a discussion of the advantages and disadvantages of such systems.