The technology being shown on the Z4 illustrate how little changes can add up when combined. By using a new, more efficient rear transaxle, the Z4 is able to record lower CO2 emissions levels and better economy. The improvements can be seen on all six-cylinder Z4s except the Z4 M, with a typical improvement of 1-2 percent across the board. Again, it's not much, but definitely a move in the right direction. Four cylinder cars get other changes to their engines that result in similar improvements. All of these eco tweaks will go into effect on cars being produced starting next month.