Audi S6 TDI test drive: the express from Ingolstadt

Audi goes against the grain with this new S6 TDI: it is neither an SUV nor a hybrid… and it still bets on a TDI engine. The result is a saloon that wins hearts with performance and driving feel, the ultimate weapon for long-distance journeys.

Tired of so many SUVs? Fed up with being sold on the advantages – which they do have, by the way – of plug-in cars? Are you one of those who doesn’t understand the persecution and hunt being carried out against diesel-engined cars? If you like going against the grain, the Audi S6 TDI is your car.

Because of the total emissions figures that manufacturers must meet across their vehicle ranges to avoid paying hefty fines, Audi has decided to bet on diesel in its revamped S range. Specifically, a new V6 TDI engine takes the place of the previous TFSI petrol engine in the new S4, S5, S6, S7 and SQ5.

However, for some markets outside Europe these S versions still feature the V6 TFSI petrol engine, which is more powerful than the diesel. But don’t worry, the new S TDI models hide a “secret” that will make you forget all about petrol.

The secret of the Audi S6 TDI: electric compressor and turbo

How can I say that when the previous Audi S6 had a 450 CV powerplant, and the new S6 TDI settles for 100 CV less?

Much of the secret lies in the combination of an electric compressor with a conventional turbocharger, which allows a maximum torque of 700 Nm to be maintained between 2,500 and 3,100 rpm, with a very high proportion of that torque already available from as low as 1,000 rpm. And that translates into tremendous power when you press the accelerator, that is, into genuinely impressive pulling capacity.

I won’t bore you too much with how the system works. If you’re interested, you can see in detail how the electric compressor works in Audi’s V6 TDI engine. What interests us this time are the sensations the Audi S6 TDI conveys when driven. That’s what this is all about. But it’s worth knowing at least that the “trick” is an attempt to eliminate the response lag of a turbocharger driven by exhaust gases, by using a compressor powered by an electric motor.

And the most important thing: it does this using a 48-volt electrical system. The same system on which Audi’s Mild Hybrid (MHEV) system is based. Yes, the Audi S6 is a “mild hybrid”, and as such it can coast with the engine disconnected in certain situations. Specifically, for up to 40 seconds while moving under the car’s own momentum, at speeds between 55 and 160 km/h. This Mild Hybrid feature allows the Audi S6 to qualify for all the benefits of the DGT ECO label.

For starters, keep these figures in mind: 5 seconds to accelerate from 0 to 100 km/h, and an electronically limited top speed of 250 km/h. Granted, the TDI “loses” half a second in the short sprint compared with the previous TFSI. I was waiting for that argument. But in a saloon weighing over two tonnes, which accelerates and handles with the agility of the S6 TDI, this shouldn’t be a problem.

Because if we’re going to look at it that way, neither the S6 TDI nor the TFSI, nor many prestigious sports cars, could boast of that if we only compared figures. A Tesla Model S P100D, for example, gets to 100 km/h in under 3 seconds. But it doesn’t overshadow the Audi S6, whatever engine it has, when it comes to sporty sensations when linking bends.

Running fast and spending little: the TDI remains the benchmark

I must admit I expected the action of the electric compressor to be more noticeable. Perhaps it isn’t because Audi has wanted to soften the engine’s response to the maximum. But honestly, from memory, it doesn’t seem much more forceful than the non-“S” versions’ V6 engine without a compressor.

However, the V6 TDI feels full across the narrow rev range that a diesel engine can offer, however sporty it may be. And this is what you miss most compared with the petrol engine. Here you’ll be working between roughly 1,500 and 4,000 rpm, almost the range where the V6 TFSI delivers its peak torque.

Again, we defend the TDI: it’s no problem at all, knowing what you’re driving. Especially if you let the eight-speed Tiptronic gearbox do its job, preferably in the sporty “S” position. The Tiptronic doesn’t encourage using the paddles or the lever in sequential mode as Audi’s dual-clutch gearbox normally does (this Tiptronic is a torque converter type), because it isn’t as quick when shifting from one gear to another. A S tronic would probably not be as smooth in gear transitions as this Tiptronic, which is also responsible for the S6 being a saloon over which the miles pass without taking a toll.

And what happens if we select the sportiest mode in Audi drive select? Well, besides the various chassis elements being set up for driving where curves are anticipated, as we’ll see later, the engine treats us to a gentle growl that aims to recall – and in a way it manages to – a petrol V8. It does this through a synthesiser emitting sound through the car’s own speakers, but if no one told you, you would hardly guess.

And now we move on to one of the S6 TDI’s main strengths: its ability to devour miles while skipping service stations. This is an area where the diesel engine remains unbeatable.

The advantage of the S6 TDI is that it can use very little fuel if you drive calmly… and it still uses little when you push the limits of the engine and chassis, especially compared with the petrol S6. On the motorway it isn’t hard to travel with an average real consumption that never reaches 7 l/100 km. And in the least favourable case possible, that is, with very sporty driving combining all kinds of roads, it’s very hard to exceed 14 l/100 km. If that last figure seems high to you, bear in mind that the previous petrol S6 TFSI in a similar situation approached figures starting with “two”.

Agile like a GTI, smooth like a luxury saloon

The chassis of the Audi S6 is the perfect complement to an engine like the V6 TDI with compressor and turbo. Of course, to achieve this, this Audi comes with an enviable technological arsenal.

I don’t think the four-wheel steering, which can be optionally fitted (around 2,500 euros), is necessary for the S6 TDI to surprise with its agility. Although with it, linking bends is a breeze. You’ll probably miss it if you try the car without it first, but more in manoeuvres than when driving.

Because the progressive steering fitted as standard already conveys precision and composure, backed up by the effective work of the suspension and by low-profile tyres (255/35 on 21-inch wheels) that have very little slip angle. The dynamic steering is more worthwhile, as it improves response in sporty driving by varying the steering ratio according to speed.

Nor does the option of air suspension seem essential, unless you’re going to use the S6 mainly for carrying passengers in the rear seats and want that feeling of gliding over a magic carpet. With the standard suspension, which includes electronically controlled damping, the S6 is firm when you need it to be, and more comfortable than you might expect for daily use.

Although it only becomes noticeable when one of the wheels slips, since initially it distributes torque in a 40:60 ratio between the front and rear axles, directing most of the engine’s power to the axle with greater traction, seeing the word “quattro” engraved on the dashboard gives a sense of reassurance that is more real than psychological.

The selective torque control system for each wheel is also standard. It brakes the inside wheels in a bend (those carrying the least load) before they can even lose traction. You won’t notice it at the wheel, because what this system allows is a higher speed through corners. And if you want more sportiness when driving at the limit, you can fit the sport rear differential, with which the S6 becomes even more agile and effective.

For the brakes, Audi uses 400 mm discs at the front and 300 mm at the rear, with six-piston front calipers. Again you can opt for an extra piece of equipment that, objectively, I only think is necessary if you’ll ever drive on a track; subjectively I won’t go into judgements, if you fancy having the very best, there’s nothing better. I’m referring to the carbon-ceramic discs, which cost over 10,000 euros. Much more powerful and durable than the standard ones, and saving almost 10 kg in weight compared with steel discs, which also benefits the work of the suspension.

Price and alternatives to the Audi S6 TDI

With a starting price of 83,090 euros, personally, one of the first alternatives I’d consider before buying an Audi S6 TDI would be… the S6 TDI in Avant version. It’s only 3,000 euros more, and the versatility this estate bodywork offers is well worth it.

Externally, the Audi S6 TDI is distinguished from the Audi A6 by specific bumpers and grille design, the mirror housings finished in silver (or black, your choice), a rear diffuser flanked by a double exhaust outlet on each side (although they are decorative, not functional) and a small spoiler integrated into the boot lid. It also features “S” badges and specific wheels.

Inside the cabin, the S version adds sports seats and steering wheel, stainless steel pedals, aluminium decorative inserts and standard features such as the top-of-the-range multimedia system, which Audi calls MMI Navigation plus. Also standard, and with a display mode specific to the S versions, is the Audi virtual cockpit digital instrumentation, which I like more every time I try it.

The refinement, finish and sophistication are outstanding. Audi manages to combine this feeling with a sporty touch masterfully, which is appreciated not only in the decorative elements, but also to the eye and touch: materials, handling, information shown on the instrumentation, configurable ambient lighting…

Among the saloon rivals of the Audi S6 in size and power, BMW offers the 540d xDrive, which has a 320 CV engine, and in the Mercedes catalogue there is the E 400d 4Matic, with 340 CV. Both feature all-wheel drive. And neither of them feels, at first glance, as sporty as the Audi S6.

You can, however, turn to the options list, more specifically the equipment offered by BMW’s M Sport line and Mercedes’ AMG line, to give these luxurious executive saloons that touch of “sport” that the S6 has as standard.

Audi S6 TDI image gallery