How is the North American version of the E46 M3 mechanically different to the European-spec model?
Unlike the E36 M3, which was equipped with a unique engine configuration for North America, all E46 M3s sold worldwide are powered by the same S54 powerplant and only differ mechanically in minor ways. The most significant difference is that the catalysts are located slightly closer to the engine block on North American-spec models, thus increasing their ability to quickly heat up and therefore minimize cold-start emissions. This accounts for the slight reduction in peak horsepower (approximately 5 hp when compared under comparable ratings standards).
