The German auto motor und sport magazine tested the most popular luxury models with diesel engines: Mercedes S 400 d 4Matic and BMW 740 d xDrive. Which is better?
Although electric models are becoming more popular, the diesel engine is still alive. Even today it is more modern and greener than ever due to modern depollution systems. In the present test, the BMW 740d with a 6-cylinder in-line engine and a 48V mild hybrid system fight against the Mercedes S 400 d also with a 6-cylinder in-line engine but without mild hybrid technology.
After experimenting with a V8 and a six-cylinder in-line with four turbos, BMW returns to more mundane things and offers a diesel with two turbines, each with variable geometry, 2700 bar injection pressure and starter generator with 11 HP and 48V network.
Like the Mercedes engine, the BMW engine has an SCR catalytic converter with two injectors, one closer to the engine and one slightly further back so that they operate in the optimum temperature range for cleaning exhaust gas both at cold start. as well as at high loads.
BMW diesel works quietly and without vibrations between 1500 and 4500 rpm, accelerates evenly and revs with pleasure, especially in Sport mode. Turbo lag? Almost imperceptible and then the electrical help from the generator starter intervenes. And the 8-speed automatic transmission does its job brilliantly while the variable all-wheel drive send all the 700 Nm on the asphalt without the slightest skid.
We have nothing to criticize for this dream diesel. But still Mercedes shows BMW what “The best or nothing” means. Although it has no electrical support, Mercedes’ engine is just as powerful. With an aluminum engine block, steel pistons, cylinder surface coating with nanoslide technology and step-combustion process, the OM656 engine is just as modern.
Depollution systems are just as powerful as BMW’s. And the 9-speed automatic transmission favors low revs. At 180 km/h in ninth gear, the S 400 d runs at only 2000 rpm as well as the 740d.
The noise level is even lower than at BMW due to the very good aerodynamics (Cx 0.22). The measurements show an advantage for Mercedes between 2 and 5 dBA depending on the speed. In practice, it impresses the exceptional sound insulation, with very low noise from the wind, the engine and from the drive train. BMW simply cannot keep up with this level of Mercedes refinement.
Instead, with the mild hybrid system, the BMW 740d accelerates a little faster and consumes less: 7.7 l / 100 km compared to 8.2 l/100 km in Mercedes. Thus, BMW has a slightly greater range of 1012 km compared to 926 at S 400 d.
With adaptive air suspension and 19-inch wheels, BMW leaves little room for improvement when overcoming short bumps, especially in terms of acoustic comfort of the suspension. Instead, after a long trip with Mercedes you come to the conclusion that no one can do better because Mercedes offers the finest absorption of short and long bumps.
We expect BMW to be more agile, especially since it was also equipped with active stabilizer bars that cannot be ordered on the S 400 d. Mercedes’ brakes are also better, the braking distances being 1-3 meters shorter from 100 and 130 km / h respectively. However, BMW offers more pronounced driving pleasure because it feels more compact and agile when cornering.
- Mercedes S 400 d 4Matic 707 pointsExtremely quiet, with soft damping and extremely refined diesel, the S-Class moves fast. The operating system is modern but access to some menus is sometimes complicated.
2. BMW 740 d xDrive 686 points
Not as comfortable and a bit more traditional in operation, BMW looks half a generation behind but is more economical and more fun to drive.