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 model year and horsepower. First of all, there is a difference in model years. The is 2 years newer. And finally, the 2016 Boxster pulls more horsepower than the 2014 Z4. Among similarities are the body structure, market segment, starting price, fuel economy, ground shadow size, height, and maximum occupancy.