Test drive Audi S6 Avant TDI, Mercedes E 400 d T: a question of perspective

Large diesel station wagons with six-cylinder engines and sporty performance

The new edition of the Audi S6 Avant is armed with a beastly diesel engine, which makes it a direct competitor to the Mercedes E 400 d T. Together with a lot of luggage, both cars carry a lot of emotions..

They say it was all just a prospect. For example, is a pear worse in terms of an apple because it's not an apple? Or vice versa? If you evaluate the Audi S6 Avant in terms of the Mercedes E 400 d T? Or T-model from Avant's point of view? At least one thing is certain - here we are comparing a dynamic model that is also comfortable with a comfortable model that is also dynamic.

How did this combination come about? The reason is that the sportiest A6 is only available in Germany with a diesel engine, and also because the sporty E-Class definitely doesn't have diesel options. However, this E 400 d in station wagon version (T-model) with 700 Nm and dual transmission is a real competitor to the S6 Avant, because even without the AMG label, this E-Class is not at all sporty. We have already established this in various benchmarking tests.

Electric air pump

Now we want to check if the T-model is equivalent to the new Audi sports wagon. Its predecessors had up to ten cylinders under the hood, and the latter had an eight-cylinder biturbo engine. Now almost everything has changed with the S6: a diesel engine, a six-cylinder engine, just one turbocharger and an electrically driven air compressor. Less power than before, but significantly more torque - 700 Nm.

If all the tears have already been shed for a big gasoline engine, we may be ripe for a sober conclusion: the conventional logic that sports models are getting bigger, heavier and, as a result, more powerful and hardly more economical. can no longer be followed with a clear conscience.

However, the diesel S6 is suitable for our time because it supports the high-performance mindset and the drive for efficiency. So if you want to travel long distances with a lot of luggage and still achieve today's single-digit average fuel consumption, you will find the right vehicle in this bulky, dynamically tunable diesel station wagon.

Are there reserves? Yes, because since the introduction of the WLTP testing procedure, for which the engines were reconfigured, we accidentally got lost in several deep "turbo pits". Diesel Audi models felt tripped, they didn’t want to accelerate, they desperately needed time at the traffic lights until the first few meters finally passed under the horns of those who were waiting behind. The manufacturer is now turning to an electrically driven air pump that has to bypass the turbocharger's initial low pressure.

The electric accelerator is located in the intake tract behind the air cooler, i.e. blows into the combustion chamber along the shortest path while the bypass system supplies it with compressed air. Thus, it fills the turbo hole of a conventional exhaust turbocharger. Isn't that what we expected?

Before we leave, let's take a quick look at the cargo bays. It may seem out of place for sports models, but before you start blaming us, we will share our credo: the luggage compartment is the only reason for the station wagon.

What we saw: the Mercedes model offers more luggage, can load more kilograms, with the backs folded down, there is a flat cargo area, and underneath it are containers for small luggage, as well as a folding shopping basket. And since the large glass surfaces improve visibility and the functions of the E-Class are easier to operate, the T-model is the winner in the body part with a significant advantage. The Avant, however, almost manages to compensate for this with its serial mates, which are available in the E-Class at an additional cost.

Wing speaker

We sit down and start the bike. In the Audi V6, the unit looks more like a six-cylinder than a diesel one. However, S-model supporters will completely calm down when they activate dynamic mode. Then a speaker under the dash and another one in the rear fender muffle the coarse frequencies with the V8 boom. Mercedes is opposed to a minimally quieter inline-six and relies on a two-stage turbo system instead of two virtual auxiliary cylinders.

Almost immediately after stepping on the gas, the smaller of the two turbos is already revving up and the E 400 d starts up a bit clumsily, and the torque increases evenly - up to those 700 Nm that are still available on paper at 1200 rpm, but also in reality only a few hundred revolutions later you will feel weak in your stomach.

That leaves a very strong impression, but it should be eclipsed by the S6, whose electric compressor rotates another 250 milliseconds after opening the throttle, according to Audi, and overcomes the lag of the single turbocharger.

Therefore, we give gas and ¬–… – you can guess from the pause in the text. It takes time for the V6 engine to produce the promised 700 Nm. The electrically driven compressor is too weak to effectively fill the turbo port. He's just getting over the recent lethargy of the WLTP - on departure, it feels like we've gone back in time before the new measurement procedure took effect. And why was this incredible technical effort necessary?

Paid extra for dynamics

The automatic machine obligingly tries to keep the bike in a high range of traction, switches willingly and above all often. This makes driving even more difficult when exiting tight bends. And overshadows that euphoria of torque that the owner bought with a promise of 700 Nm. Here, you expect a calm and confident mid-stroke, but instead you get active turnover.

Maybe this is the reason for the 0,7-liter higher average consumption per 100 km, but the S55's weight, which is 6 kg higher, probably plays a role. However, looking at the analysis of the road dynamics tests is surprising: the T-model does not lag behind the sporty Avant, and on both lane changes, even one idea faster. Even later, in fast cornering, the E 400 d does not allow the S6 to come off, follows it without any problems and at the same time remains completely calm, like its driver.

Consolation for Audi fans: The S6 feels more lively and refreshing, thanks to more direct steering and a stiffer chassis, as well as extras like swivel rear wheels (1900 euros) and a sporty differential. (1500 euros), providing a kind of torque vectoring. The extra torque on the outside rear wheel in the corner spins the rear end, which on the one hand makes the S6 change direction more spontaneously, and on the other hand gives the border area a certain exhilarating uncertainty – sometimes the rear end leans more than you think.

With subjectively perceived driving pleasure, the T-Model remains a little understated because it turns almost all corners. The change of direction seems to happen on its own. At the same time, the slightly uneven action of the electric power steering is impressive. This was not the case in the E-Class. Is it because the front wheels of the 4Matic test version also perform drive functions?

On the other hand, the model drives Mercedes on the highway with stubborn straightness, even when the Audi representative requires minor adjustments to the steering wheel. And he cares more about his passengers. The rougher the waves on the pavement, the more they irrevocably lose their meaning due to their air suspension (1785 euros).

To put it simply: the agility of the S6 costs 2400 euros, while the comfort of the E-Class costs an additional 1785 euros. Both vehicles are expensive to manufacture, but not well equipped to go into battle from a manufacturer's point of view. Both companies sent samples with acoustic glazing and additional seats for testing. In addition, the T-model increases mileage due to a larger tank. Accordingly, when evaluating the S6 Avant, we quote 83 euros as the base price, and 895 euros for the E 400 d T. And the fact that an Audi model tends to be better equipped from the factory is evident from its point advantage in the equipment section.

And when you put it all together, the S6 ends up missing six points of traction—and it lost them because of its bike. The V6 accelerates more subtly, is more fuel efficient, produces more emissions and incurs slightly higher fuel costs.

Not only from the point of view of the Mercedes V6 disappoints the engine of the Audi S6. Whether it's diesel or not, in the sporty model, the transmission should do its job more willingly - at least like a conventional six-cylinder E 400 d T engine.

Text: Markus Peters

Photo: Ahim Hartmann