What's all this about?
Oh, nothing much. Just BMW announcing a new 7 Series with four turbochargers.
Four?!
Yes indeed. The 750d and Ld models - due out this July, and both featuring xDrive all-wheel drive and eight-speed automatic gearboxes - use the familiar 3.0-litre inline six-cylinder diesel engine that has seen service in BMWs for all of the 21st century (in one guise or another), but whereas the most potent example before had three turbochargers, this one packs four of the blighters. The results are lots of power, oodles of torque and M-car rivalling performance, yet economy near 50mpg.
Really? It blends all these things together?
It does. Choose the regular wheelbase 750d and it will thump from 0-62mph in 4.6 seconds, running on to a limited 155mph maximum that's probably well within what it would be capable of if it were allowed to gallop unfettered. Expect to see 49.6mpg and 149g/km of CO2 emissions in this guise. If you need a bit more legroom in the back (as in, if you need to hold a party in the rear footwells of your Seven), then the 750Ld has the same top speed as its short-arsed sibling, with only minor impairments to its other figures, recording 0-62mph in 4.7 seconds, 47.9mpg and 154g/km.
Wow! How much power does it have, then?
Not much more than the old triple-turbo, with gains of 19hp and 20Nm over its predecessor leading to final outputs of 400hp at 4,400rpm and 760Nm from 2,000- to 3,000rpm; more pertinently, 450Nm of that torque is accessible at just 1,000rpm. We would hazard a guess that even more punchy variants of it will appear before too long, so don't be surprised if this quad-turbo monster starts knocking on the door of 500hp in the years to come.
Four turbos... does that make it the first of its kind?
It's the first diesel to ever sport so many forced induction 'snails', although there have been three petrol cars that can match the 750d's turbo count. And they're all Bugattis - the V12 EB110 of 1991, and then the W16-powered Veyron and Chiron hypercars of the modern era.
That's some fine company. How do all these turbos work on the BMW?
Taking the triple-turbo layout from the previous engine as the basis, instead of two small low-pressure turbos (LPTs) and one giant high-pressure turbo (HPT), the 750d splits the high-pressure unit into two medium-sized HPTs. Under general driving, the BMW will be using both its LPTs and one of the HPTs, with the final turbo joining the fray once the engine spins past 2,500rpm. Common rail injection on the quad-turbo runs at a massive 2,500 bar, while the 750d has a diesel particulate filter, a NOx storage catalytic converter and a Selective Catalytic Reduction (SCR) system with AdBlue injection to keep its exhaust gases nice and clean.
This sounds brilliant. When does it go on sale?
In July of this year. BMW says that adding exhaust gas recirculation for the LPTs (it was previously only used in the high-pressure cycle) eliminates lag. We can't wait to find out if that's true.
Matt Robinson - 17 May 2016
