Bovensiepen 05 GT driven: 790bhp successor to the Alpina B5

Meanwhile the twin-turbo 4.4-litre petrol V8 gets new intake plumbing and a titanium Akrapovic exhaust from the silencer back. It alone is responsible for the 05 GT’s 72bhp uplift over the regular M5’s output. Flybys at the Salzburgring racetrack, where we drove the 05 GT, were riotous events reminiscent of low-flying jet aircraft.

Elsewhere, the M5’s M Adaptive dampers have been retuned and the 05 GT is fitted with its own bespoke Eibach springs, as well as new strut-tower braces. The staggered wheel set-up of the regular M5 is also dispensed with and 21in alloys (with milled spokes) are fitted all round. Model-specific ‘BOV’-marked P Zero R tyres, bespoke from Pirelli, complete the package with an M5-matching contact patch.

Bovensiepen doesn’t tinker with the tuning of the steering or the rear-steering, or the four-wheel drive system, which behaves as per the regular M5, with its myriad of modes and traction control settings.

What it has tinkered with, and tinkered well, is the styling. This is the work of Frank Stephenson’s studio and it offers a wholesale revision of the standard car’s porcine thuggery. A black pin-stripe down the flanks – along with the concave sills intended to reduce visual weight – is bookended by subtly sporting bumpers and neat roof spoiler. It will take a while for a bumper script that reads ‘Bovensiepen’ rather than ‘Alpina’ to feel normal, but this is a smart styling effort that strikes the right tone on a challenging canvas. 

Which brings us to the interior, where it is a similar story to the outside. All the saddlery expertise that the Bovensiepens accrued while in command of Alpina has been brought to bear and it is superbly plush in here, with endless potential for customisation, including embossing of the headrests. It’s just a shame that the donor car is so plastic-heavy across the dashboard. It cheapens the ambience, though this can hardly be held against Bovensiepen Automobile, whose diligence in maximising comfort extends to offering several tyres of piping for the upholstery. 

Comfort is something the 05 GT ought to do well on the road. We won’t know for certain until we drive one in the UK, but the way this revised chassis dealt with the fiendish undulations of the Salzburgring was promisingly languid but underpinned with confident-inspiring control. That said, Bovensiepen ought to offer 20in wheels with a little more sidewall, just to be on the safe side in terms of secondary ride. Unfortunately, a grand total of six laps doesn’t permit much more in the way of meaningful real-world dynamic analysis. 

Performance? Monumental; move on. Towards the end of the day, a familiar pattern unfolded during a few spirited laps with one of Bovensiepen’s factory hot-shoes in a Zagato prototype. The 05 GT would have unnerving stability in the big brake zones. It would then turn in beautifully for a big car, only to fall off the back of the Zagato as its nose-y balance and weight counted against it on the way to the apex. Then, once rotated, it would inexorably reel in the smaller coupé on the exit like a Lancaster bomber bearing down on a microlite. It is just monstrous and has the depth of performance and monolithic composure that tends shrink big miles with ease.