Two Convertibles with some similarities, but otherwise different in most aspects such as the modifications, model year, horsepower, fuel economy, 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 2014 GranTurismo Convertible Sport. Also, you'll seat two more passengers in the GranTurismo Convertible Sport than in the SL-Class SL 63 AMG. Among similarities are the body structure, market segment, starting price, ground shadow size, and height.