The 2010 SLK-Class is a 2-door, 2-passenger convertible sports car, available in 3 trims, ranging from the... SLK300 Roadster to the SLK55 AMG Roadster. Upon introduction, the SLK300 Roadster is equipped with a standard 3.0-liter, V6, 228-horsepower engine that achieves 18-mpg in the city and 26-mpg on the highway.