BMW Alpina B6 Bi-Turbo Convertible (2011) at the Frankfurt motor show

BMW’s M Division is busy readying M6 variants of both the 6-series Coupe and Convertible, but if you can’t wait until 2012 – or if you want a fast but understated Six – then Alpina has just the car for you. It’s the BMW Alpina B6 Bi-Turbo Convertible, just unveiled at the 2011 Frankfurt motor show.

Indeed it does. Just as BMW launched the drop-top version of the 6-series ahead of the hardtop, so its favoured aftermarket ‘upgraders’ (tuners is such a ugly word to use in conjunction with the exquisite work that Alpina does) have launched the B6 Convertible first. A B6 Coupe will follow.

Under the bonnet is a 4.4-litre twin-turbo V8, identical to the unit found in the B5 saloon and Touring, which is itself pretty similar to the engine that powers the new BMW M5. But so M Division’s M5 and forthcoming M6 are not found wanting, the Alpina B6 makes do with ‘just’ 500bhp – the M cars have 552bhp. There’s 516lb ft, at 3000-4750rpm, while the M engine counters with 502lb ft from 1500-5750rpm.

The Alpina's power goes to the rear wheels via an eight-speed automatic gearbox, the 0-62nph sprint takes 4.8 seconds, and the top speed is a baldness-inducing 194mph. Perhaps more impressively, the official figures are 25.9mpg and 255g/km, not far off the 26.4mpg and 249g/km achieved by BMW's 401bhp 650i.

Finally, the B6 also sports a set of four ultra-expensive but lightweight titanium exhausts from Akrapovic, which already supplies pipes to BMW’s M car MotoGP fleet.

By Ben Pulman