Two Sedans with more similarities, such as the body structure, market segment, starting price, ground shadow size, and height, than differences, like the powertrain, horsepower, and fuel economy. First of all, the 2016 BMW 7 Series has bigger and thirstier engine; the 2015 Audi A8 Diesel gets 7 more mpg. Among similarities are the body structure, market segment, starting price, ground shadow size, and height.