Road test: Audi SQ7 & Bentley Bentayga Diesel

New engine adds serious urge to related but very different cars

However they might appear in the flesh, the biggest difference on paper between the Audi SQ7 and Bentley Bentayga diesel is their respective price points. At £135,800, the Bentley costs almost twice as much as the Audi, before extras that can push that price towards £200,000 with terrifying ease.

This despite the fact both cars sit on the VW Group’s full-sized MLB hybrid steel and aluminium architecture, and share the same suspension configuration, the same 4-litre V8 diesel engine and the same eight-speed ZF gearbox.

But before we delve deeper into what separates them in reality, we need to look a little harder at the technology, because it is genuinely fascinating.

The engine in particular is a fiendishly clever device, the most powerful diesel motor in production and by a decent distance the most sophisticated too. Superficially it’s a twin-turbo V8, though it uses those turbos sequentially, not in series. There is nothing new in this – BMW among others has been doing it for ages – but I still don’t understand why more don’t embrace the idea of a small, low-inertia turbo to limit lag at low engine speeds, progressively handing over to a more meaty puffer as revs rise. In the Audi and Bentley cases, it’s a twin-scroll unit that does the work, and does it well. Regardless which one you drive, it will place 429bhp under your right foot.

But when you drive either, it is not the power you feel but, appropriately for these kinds of car, the torque and the unique way in which is delivered. Not only is there 664lb ft of the stuff, which is as much as the 6-litre 12-cylinder twin-turbo engine from the petrol Bentayga can deliver, it’s all there at 1000rpm. Which is unprecedented.

It’s possible because the car is actually triple-charged: it has two conventional turbos plus a third device that’s neither a turbo (it is not exhaust-driven) nor a normal supercharger (it’s not driven directly from the engine). Instead it is
an electric compressor driven by a completely independent 48-valve subsystem using power from a lithium-ion battery pack, the same system that also allows the front and rear anti-roll bars to disconnect themselves when the car is travelling in a straight line for ride comfort or in many off-road conditions, and recouple the moment cornering forces require it. Make no mistake, this is clever stuff and two senior engineers from unrelated companies have confessed to me their envy for this system.

Despite the fact that both Audi and Bentley share identical powertrain hardware, Bentley says it has taken a radically diverse approach in terms of tuning and I’m sure it does respond differently relative to which drive mode you decide to use in each car. But that’s not the point. The point is that it imbues either car with performance that would disgrace many an expensive sports car and, in a pair of 2.3-tonne SUVs, that performance is simply shattering.

So instantly does the engine respond from such preposterously low engine and road speeds, the cars to which it is fitted can feel more closely related to pure electric machines like Teslas than conventional turbodiesels. When you first make your acquaintance, the torque delivery has an addictive quality and even when you’re quite used to it, it never quite loses its novelty value.

What effect, then, does this powertrain have on the cars themselves? For the Audi, it is transformative. I would rank a standard diesel Q7 squarely in the middle of its class, clearly less desirable than a Range Rover Sport but at least competitive with its Mercedes-Benz and BMW rivals. It’s a car of few distinguishing features that just quietly and efficiently gets on with the job in hand. Equip it with the diesel motor, however, and every journey becomes an event because you don’t have to be driving fast to feel what the engine does best.

The effect it has on the Bentley is more subtle, because if you’ve driven another Bentayga, it can only be the 600bhp W12 flagship. The additional low-down response is welcome and a very Bentley characteristic, but I expect owners will appreciate most the fact that it will do a genuine 30mpg in conditions where you couldn’t hope for 20mpg from its petrol stable-mate. I don’t imagine they’ll care much for the cost saving, but the fact it will go half as far again on a tank of fuel is likely to be a source of continual delight. Calais to the Alps in one hit is now a real possibility.

And no, of course you can’t justify the extra cost of the Bentley in objective terms. The Bentley seems more solid, appears to go down the road even more quietly and ride with a touch more sophistication, but I’d be the first to admit this could all just an impression provided by its swaddling nature of its deeply luxurious interior. Without driving both back to back, which I was unable to do, I couldn’t say for sure.

So you’re paying for a name, a look (which I happen not to like), exclusivity and a sense of occasion. The truth is that for all its extraordinary technology, the Audi Q7 remains a beast of family burden, a functional device for doing a specific job. And it’s a job it does impressively well and with real elan. But the Bentley is a home from home, a place you’d actually choose to spend time, regardless of road or traffic conditions. The wood, the leather and what Bentley likes to call handcraftsmanship, really do count. Enough to justify the price? Customers are voting with their chequebooks, forming such long queues for Bentaygas it’s likely to outsell all other Bentleys combined and push production to 20,000 units by the end of the decade. For a company that produced a mere 1000 cars as recently as 2003, that’s some transformation. And put in the happy position of having to choose between Bentaygas diesel or petrol? Even without the £25,000 price gulf that separates the two, I’d have the diesel every time.