Is The BMW 8-Series Gran Coupe Better With A V8 Petrol Or An I6 Diesel?

A little over a year ago, I stuck my neck out to suggest that the BMW 8-series works better with a diesel inline-six than a petrol V8. Today, I’d once again like to get into the 8er diesel vs petrol debate, but don’t panic - this isn’t a case of Morpheus-troubling deja vu.

This time, it’s the 8-series Gran Coupe we’re talking about, rather than the shorter two-door version of the 8. Plus, the personal context isn’t quite the same. I’ve spent about five months with an 840d GC (admittedly, it didn’t move a whole lot for a month and a half of that), and have since switched to an M850i GC.

After first making the swap, I wasn’t sure it felt much quicker, despite the M850i having an additional ~200bhp to play with. A total of 513bhp, to be exact. The 840d being damn near as torquey as its V8 sibling will be part of that; it churns out 502lb ft, versus the M850’s 553lb ft.

Get out of the similarly punchy mid-range and venture into the top end, however, and the petrol engine’s extra potency becomes clear. It’s an absurdly quick car for something weighing around two tonnes, hitting 0-62mph in 3.9 seconds, a drop of just two tenths relative to the lighter coupe.

The delivery is addictive. Turbo lag is barely perceptible, and the howling noise is more akin to a chunk of modern eight-cylinder Americana than something hailing from Munich. In terms of handling, the setup doesn’t differ a whole lot from the diesel; it still does a commendable job of feeling smaller and lighter than it actually is (all-wheel steering certainly helps in this regard), even if it’s not entirely able to mask the bulk.

The extra thrust of the V8 taxes the all-wheel drive system more, though, making it easier to get some movement from the rear axle. Factor in the added venom with which it can spit you out of a corner, and you have a very different driving experience.

However, it comes down to the same issue we had with the M850i coupe; the shouty, responsive V8 seems at odds with the rest of the package. BMW clearly wants this to be a grand tourer, and that desire is merely amplified with the more practical Gran Coupe and its stretched wheelbase/extra doors.

On the GT front, it doesn’t quite hit the mark, either. The 8er is a fine cruiser whatever engine you stick in it, but it’s a long way from Mercedes S-Class coupe levels of waft, plushness and refinement.

The biggest issue for the M850i - in all three of its body styles - is the price. In Gran Coupe form it’s £99,991 before you’ve started adding options, putting it in range of the £107k Porsche Panamera GTS, which is a far sportier feeling car that’s no less comfortable.

Coming in at a much more reasonable £72,155, the 840d is far easier to recommend. So too is the similarly priced 840i which, with its lighter inline-six petrol engine, is the nimblest GC of the lot.

And yet, the M850i GC is the one I’m drawn to most. Of all the 8ers I’ve sampled - M8 Competition included - it’s the one that provides the best all-round enjoyment. It makes little sense and there are plenty of better ways to spend your money, but it might just be my favourite thing that BMW makes right now.