German BMW tuner creates a powerful twin-turbo 6er cabriolet with 507 PS (373 kW / 500 bhp) and 700 Nm (516 lb-ft) of torque.

Official BMW re-manufacturer Alpina has previewed the B6 Bi-Turbo Cabrio, based on the 6-Series convertible.

Alpina takes BMW's 4.4 liter V8 and adds its own twin-turbo system to dial output up to 507 PS (373 kW / 500 bhp) at 5,500 rpm and reach a torque rating of 700 Nm (516 lb-ft) between 3,000 and 4,750 rpm.

The B6 Bi-Turbo gains 100 horses and 100 Nm over the BMW 650i Cabrio (the most powerful 6-Series convertible currently available) and reaches 100 km/h in just 4.8 seconds. Top speed is also a healthy 311 km/h (193 mph). Fuel-economy is a reasonable 10.9 liters/100 km with a CO2 quotient of 255 g/km.

Look for the B6 Bi-Turbo Cabrio to debut at the Geneva auto salon next year.