As the pressure to reduce fuel consumption and carbon dioxide emissions continues unabated, it's not just gasoline engines that are getting the right-sizing treatment. The diesel engine is set to shrink as well, at least at BMW and Mercedes-Benz. Both manufacturers currently offer diesel V-8s of 4.4L and 4.0L sizes respectively in their top models. However, both companies are likely to start replacing their current diesel model range with newer, smaller displacement alternatives with new boosting technology that will improve the power while reducing fuel consumption. That means following the path BMW has been traveling recently with sequential twin turbocharger systems such as the one on the 123d. These setups use a pair of different sized turbos that help to enhance torque at both low and high revs. This will allow the V-8 to be replaced by inline and V-6 cylinder engines while current six cylinder applications will go to fours. All of these will also likely be combined with mild hybrid systems for even more improvement. Besides the improved efficiency of the smaller engines, weight will also be reduced, further enhancing fuel economy. So far, the one exception to this trend is Audi which just announced production of the Q7 V-12 TDI with its new 6.0L V-12 diesel. That however will be a very low volume application and more mainstream units will probably go the downsizing route.