They practically redesigned the exhaust system for the American models. I asked him about this earlier today, apparently the hotter/higher compression (i.e. more efficient) the diesel engine the more NOx they put out, CA Air Advisory Board is obsessed with NOx emissions.pretty sure most companies are making the same version of diesel car for both markets and they're being designed to address the different standards in one engine. for instance, the bluetec mercedes engines are the same here and there I believe