It hasn’t been long since the very idea of a diesel-powered Bentley SUV would have been regarded as the sort of heresy that gets angry mobs lighting up their flaming torches and heading for the creepy castle. Yet the Bentley Bentayga diesel is a thing—albeit one that will be denied to us—and after driving it in the United Kingdom, we can report that the new engine suits the luxurious beast almost perfectly.
the Audi SQ7 that shares it, and it was engineered to meet all appropriate federal standards. But then Dieselgate happened, and the Volkswagen Group decided that none of its brands would sell any more compression-ignition engines on this side of the Atlantic. So the Bentayga diesel finds itself on the long list of Awesome Cars Unfairly Denied Us.
This is a shame, mostly because this might well be the greatest compression-ignition engine ever fitted to a passenger vehicle. Technically, the propulsion unit is identical to that in the Audi SQ7, meaning that it’s a V-8 displacing 4.0 liters and has sequential turbochargers that use a clever variable-valve system to bring the second turbine on boil. These are further assisted by a 48-volt electric supercharger which, basically, is a 9-hp motor that sits downstream of the intercooler and can spin a centrifugal-flow compressor up to 70,000 rpm in less than a quarter of a second to reduce turbo lag to the barest level of detectability.
The result is an engine with a character akin to that of the old turbocharged 6.75-liter pushrod gasoline V-8 that Bentley formerly installed in cars such as the Arnage. Like that six-and-three-quarter-liter engine, the TDI isn’t built to rev, although it pulls cleanly to its limiter at 5000 rpm. It does generate enormous low-down torque, delivering the peak 664 lb-ft over a wide band starting at just 1000 rpm.
Yet the diesel also manages to be more refined than its gasoline grandfather ever was, emitting nothing louder than a purposeful growl even under the hardest use. The biggest difference is fuel economy, which is unlikely to be much of an issue for anyone with the considerable wherewithal needed to fund any Bentayga purchase, but it’s still a neat party trick. If this were certified by the EPA, we estimate it would get about 26 mpg on the highway—a figure that, in conjunction with the 22.5-gallon fuel tank, gives the Bentayga diesel a range that can fairly be described as Continent crushing in terms of geographic reach.
The torque peak is identical to that quoted for the W-12 version, although that’s more likely electronically limited by the limits of the eight-speed automatic transmission rather than a spooky coincidence. While the diesel is significantly deficient in power by comparison—its 429-hp rating is 171 shy of the W-12’s output—it lacks little in real-world pace. Or, indeed, absolute speed: Bentley quotes a 4.6-second zero-to-60-mph time. (We recently ran the W-12 model to 60 mph in 3.6 seconds against a claimed 4.0 seconds to 60.) The diesel’s top speed of 168 mph likewise is some way off the W-12’s 187 mph, but we suspect that owners will rarely feel the lack. It’s also worth noting that we experienced none of the surging or lag we detected when we tested the W-12; on everything except cylinder count and peak output, this is the better engine.
Bentley says the diesel is slightly heavier than the W-12 thanks to the iron block and the additional supercharger. All those pounds become most obvious when slowing down—or, rather, when not. The gearbox has a sail mode that declutches when the car coasts, and the Bentayga feels as if it could roll several miles on nothing more than its own momentum. We experimented with using the transmission’s manual mode to lock it into eighth gear, which created a far more natural-feeling deceleration curve but also proved that the engine will pull cleanly from just 1000 rpm.
The infotainment system also deserves some mild chiding. It’s a Bentleyized version of the previous-generation Audi system, and although entirely adequate it feels old and somewhat clunky. Strange that the $200,000 car that sits at the top of the Volkswagen Group’s SUV hierarchy has a system that’s inferior to the one in its $100,000 cousin. The new Continental GT is switching to a version of Audi’s current class-leading MMI, so it is likely the Bentayga will follow shortly behind.
In future years, Europe’s current love for diesels likely will be seen as a historical blip; even before the scandal, diesel emissions standards were tightening, and sales had begun to decline. The controversy, of course, dramatically sped up the process not only in America but in many other countries where diesel was once considered the answer for reducing carbon emissions. It’s unlikely that any automaker will ever devote the considerable funds necessary to create a better diesel engine, meaning that the Bentayga diesel’s position at the very top of the tree probably never will be challenged.