Two Convertibles with some similarities, but otherwise different in most aspects such as the model year, modifications, horsepower, fuel economy, ground shadow size, height, and maximum occupancy. First of all, a bigger engine usually means less mpg. But the 2016 SL-Class SL 63 AMG has a more powerful engine and it gets 4 more mpg than the 2013 GranTurismo Convertible. Also, although the GranTurismo Convertible is slightly smaller, it has a taller body than the SL-Class SL 63 AMG. In addition, you'll seat two more passengers in the Maserati GranTurismo Convertible than in the Mercedes-Benz SL-Class SL 63 AMG. Among similarities are the body structure, market segment, and starting price.