The spark-ignition petrol engines listed below operate on the four-stroke cycle, and unless stated otherwise, use a wet sump lubrication system, and are water-cooled. Since the Volkswagen Group is German, official internal combustion engine performance ratings are published using the International System of Units (commonly abbreviated "SI"), a modern form of the metric system of figures. Motor vehicle engines will have been tested by a Deutsches Institut für Normung (DIN) accredited testing facility, to either the original 80/1269/EEC, or the later 1999/99/EC standards. The standard initial measuring unit for establishing the rated motive power output is the kilowatt (kW); and in their official literature, the power rating may be published in either the kW, or the metric horsepower (often