Two Convertibles with more similarities, such as the body structure, market segment, starting price, fuel economy, ground shadow size, height, and maximum occupancy, than differences, like the horsepower. And finally, the 2016 Porsche Boxster has a more powerful engine than the 2015 BMW Z4. Among similarities are the body structure, market segment, starting price, fuel economy, ground shadow size, height, and maximum occupancy.