BMW has been making diesel cars run faster for over a decade now. We know they have a 400-PS 3.0-litre quad-turbo M550d, but that's another level. What they also have is the all-new G30 5 Series with a TwinPower Turbo straight-six diesel engine that's smooth as butter. The new specification sees a seven-horse jump in power, but a full 60 Nm of torque more. Unlike a V6 or an in-line four, there's no real audible clatter. The engine is near inaudible inside the cabin.