Which BMW 8 Series is better: diesel or petrol?

Diesel-powered performance- or luxury cars never really took off in South Africa, with many of this segment’s pioneers cut down right when technology finally taught the diesel engine some manners and got it to stop smoking. But some manufacturers still persevered with diesel, and did a really good job with it, even in the face of the internal combustion engine’s expected imminent demise.

Related: The top 4 BMW 8 Series features that stand out from the competition.

 

BMW is one such manufacturer, and their excellent 3.0-litre turbodiesel is consequently used in all their model ranges from the 3 Series up, with varying turbo counts to achieve different outputs. It’s even found its way into the range-topping 8 Series – albeit only in Gran Coupé (4-door fastback) form for our market.

We also don’t get the best version of this engine in any 8 Series, with the 294 kW/760 Nm quad-turbo variant remaining exclusive to SUVs and sedans from the X5 and 5 Series upwards. How well does diesel power suit the BMW 8 Series, though, and is it really a viable alternative to its petrol siblings?

To find out, we decided on using the Gran Coupé (GC) body style as a reference, because it’s the only version to feature the inline-6 diesel (in twin-turbo “40d” form), and it’s also the body type that offers the widest range of available 8 Series engines. Before we decide which one is better, let’s first look at the numbers.

 

	BMW 840i GC	BMW 840d xDrive GC	BMW M850i xDrive GC
Engine Type	3.0-litre inline-6, single-turbo petrol	3.0-litre inline-6, twin-turbo diesel	4.4-litre V8, twin-turbo petrol
Power/Torque	250 kW/500 Nm	235 kW/680 Nm	390 kW/750 Nm
Performance Data *	0 – 100 km/h in 5.2 seconds	0 – 100 km/h in 5.1 seconds	0 – 100 km/h in 3.9 seconds
Fuel Consumption *	7.9 ℓ/100 km	6.7 ℓ/100 km	10.7 ℓ/100 km
Price **	R 1 547 230	R 1 633 278	R 2 060 000

* Manufacturer’s claimed figures for performance and average fuel consumption.
** Base trim prices including emissions tax; accurate at the time of writing, but may change without prior notice.

 

Which engine suits the BMW 8 Series best?

Observant readers will notice that the table above doesn’t include the M8 Competition, which also happens to be available in Gran Coupé form. There’s a simple reason for this: if you can afford to buy or lease, insure and fuel one of those, it’s the best engine you can get in an 8 Series, full stop.

It’s excluded for this reason – the M8 is pitched as a distinct model rather than as a mere part of the 8 Series line-up, and it’s sufficiently differentiated from the mainstream variants to justify that market positioning. Let’s concentrate on the slightly more-sensible engines instead, and then decide which one is best suited to which role in the range.

Related: Take a joy ride in the thundering BMW M8 Competition Coupé with this review.

 

BMW 840i Gran Coupé

This is the entry point to the 8 Series, and has two unique features: it’s the only one with a 6-cylinder petrol engine, and it’s the only one with rear-wheel drive. As a consequence, it’s a fair bit lighter than the others (125 kg lighter than the next-up AWD 840d), helping make the most of the 250 kW and 400 Nm on tap from the 3.0-litre single-turbo engine.

These stats make for a decently quick car, with a 0 – 100 km/h sprint in only 5.2 seconds, and a top speed that’s governed at 250 km/h. It should even be reasonable-ish on fuel: the official numbers claim an average consumption of 7.9 ℓ/100 km, although we’d expect closer to low-9 ℓ/100 km figures in real-world driving.

Related: This comprehensive review will tell you everything about the classy BMW 840i Gran Coupé.

 

 

BMW 840d xDrive Gran Coupé

About R 80 000 extra buys the sole diesel option in the local 8 Series range, and it comes with both benefits and downsides. Peak power is down slightly, measuring 235 kW in twin-turbo “40d” format, but there’s a handy pile of extra torque – 680 Nm of it, to be exact.

This hands the 840d a nice advantage in mid-range acceleration, and combines with the traction available courtesy of the AWD system (the sole drivetrain), to give respectable standing start sprints. 0 – 100 km/h is achieved in a claimed 5.1 seconds, and its top speed is again limited to 250 km/h. It’s also a fair bit less thirsty than the 840i, with a claimed average consumption of 6.7 ℓ/100 km, which is pretty good for a large luxury car that it weighs a cool two tons in base trim.

Related: Get more detail about the BMW 8 Series range in this launch report.

 

BMW M850i xDrive Gran Coupé

It’s potent enough to deserve M-car status, and it’s a lot less expensive than the full-fat M8, all of which makes the M850i an appealing option in its own right. Sure, the Gran Coupé isn’t quite as sexy as the real 2-door Coupé or convertibles, but it comes close enough, costs less, and offers a lot more usable space.

And, as with the M8, we’d say that, if your budget allows for buying and running one of these, it’s absolutely worth it. R 2-million and a bit sees the engine upgraded to a twin-turbo V8 petrol, bumping outputs to 390 kW and 750 Nm.

That endows the top non-M 8 Series with a claimed 0 – 100 km/h sprint in only 3.9 seconds, again with a limited top speed. Be prepared to feed the beast within, though, with a claimed average consumption of 10.7 ℓ/100 km but a real-life average sure to be closer to 15 ℓ/100 km – especially if the available pile of power is deployed with any frequency.

Related: Larger than life – we review the BMW M850i convertible.

 

The Verdict

It’s not an entirely logical exercise to try and determine “the best” from these three variants, because they have different priorities. Taken as a complete package, the 840d xDrive makes the most sense: it’s not a huge lot more expensive than the 840i, but it has a very useful mountain of torque from one of the nicest diesel engines out there (that also saves a fair bit at the fuel station), and adds sure-footed AWD traction. Mixed with the surprisingly practical “4-door coupé” body style, it’s the one that ticks most of the sensibility boxes.

However, a car like a BMW 8 Series isn’t really about sensibility, so the 840d’s main appeal might be a moot point. Keen drivers might find the lighter, RWD-only 840i with its sweet-revving straight six petrol to be a more-engaging experience, while power addicts will be very satisfied with the M850i’s V8 muscle car aura. At a cool R 1.25-million less than the M8 Competition, you could even say that M850i looks like a performance bargain...

 

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