The unrelenting progress of diesel engines shows no sign of flagging. Witness BMW’s brilliant new twin-turbo 535d. Ignore the capacity implications of the 535d badge and the still-3.0-litre in-line six reclaims the title of the world’s fastest-accelerating diesel car from Audi’s A8 4.0 TDi.
Not only that, it introduces new levels of responsiveness, an even broader powerband and the highest specific output – a staggering 90bhp per litre – of any current production diesel.
The 535d is so powerful it outguns even the 255bhp 3.9-litre V8 currently offered only in the left-hand-drive 740d. Understandably, the V8 is due to be enlarged for next year’s revised 7-series. The new six uses twin turbos of differing sizes.
A small turbo operates alone from idle to 1500rpm, when it’s joined by the big turbo for a short second stage, before the larger blower takes over from 2500rpm to the maximum 5000rpm. So the new BMW unit is entirely different from Jaguar’s 2.7-litre diesel, which effectively operates as two three-cylinder engines, each with its own identically-sized turbo.
No doubting the result. The peak figures are an impressive 268bhp at 4400rpm and 413lb ft at 2000rpm. But more revealing of the engine’s sporting character are these numbers: at 1250rpm, it’s already pumping out 369lb ft, matching the 530d’s maximum torque (developed at 2000rpm). Yet there’s also 241bhp (up 26bhp on the 530d) on tap as high as 4800rpm.
So potent is the 535d that BMW’s manual gearbox can’t cope with the extra torque. When the saloon and estate versions go on sale in October – expect a premium of around £3175 over the 530d SE autos – they’ll be auto only, the ZF six-speed beautifully matched to the engine’s personality.
Turn off the traction control to play hooligan and the 535d lights up the back wheels, belting to 62mph in 6.5sec. That’s almost a second faster than the 530d auto, 0.6sec ahead of the manual, and undercuts the A8 TDi by 0.2sec.
Not that the new engine is just about bottom-end punch – like VW’s 553lb ft V10 TDi – this diesel delivers near-linear power from idle all the way to 5000rpm, without the driver ever being aware of the turbo changeover point.
And across this unrivalled span, the throttle feels responsive – forget turbo lag – and the performance is swift, the auto’s brain downshifting below 1500rpm to ensure the car’s always in the most suitable gear. On German autobahns, it quickly runs to an indicated 160mph.
Who needs a petrol 545i? If the new diesel lacks the supreme refinement of Jaguar’s V6, it’s smoother than the 530d, and the powerful growl is perfectly suited to the BMW’s character.
It’s been six months since I drove a 5-series. Coming back confirms that the Active Steering requires more than a day’s driving before it feels intuitive. Seems BMW, too, is having second thoughts: expect a less direct parking ratio – currently 1.7 turns – to be quietly slipped into the Five in a few months.