The Mercedes-Benz S550 was a variant of the W221 S-Class that was introduced for the 2007 model year. The S 550 was sold as the S500 outside of North America and was available in rear wheel drive or all wheel drive (4Matic) layouts. It was initially powered by Mercedes' M273 E55 engine. The M273 E55 was a 5.5L naturally aspirated V8 engine that generated 383hp. This engine was replaced in 2011 for the M278 engine, which was a 4.7L twin-turbo V8 engine that produced 429hp. The W221 S550 was built until 2013, although the model series would continue in the next generation W222 Mercedes-Benz S-Class as the W222 S550