Porsche hasn't traditionally been associated with diesel engines, but that's changing. Now the company has put a diesel into its 4-door Panamera touring sedan. BMW, on the other hand, started delivering its biggest cars with diesels 15 years ago. The two cars we test both have 184 kilowatts under the hood and almost identical performance figures. But which car offers more in terms of comfort, sportiness and fuel efficiency? drive it! found the answer.