The Alpina B6 Cabrio (E64) 4.4 V8 (500 Hp) Switch-Tronic is a high-performance luxury convertible produced by the German automotive manufacturer Alpina between 2005 and 2008. Based on the BMW 6 Series (E64) convertible, the B6 represents Alpina’s interpretation of a grand touring vehicle, blending substantial power with refined comfort. It occupied the top echelon of the 6 Series range, offering a more exclusive and potent alternative to BMW’s own offerings like the 650i. The B6 Cabrio was part of the broader Alpina B6 lineup, which also included coupe versions, all sharing the same core powertrain and performance enhancements.
Technical Specifications
| Brand | Alpina |
| Model | B6 |
| Generation | B6 Cabrio (E64) |
| Type (Engine) | 4.4 V8 (500 Hp) Switch-Tronic |
| Start of production | 2005 |
| End of production | 2008 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (economy) – urban | 18.9 l/100 km (12.4 US mpg, 14.9 UK mpg, 5.3 km/l) |
| Fuel consumption (economy) – extra urban | 9.3 l/100 km (25.3 US mpg, 30.4 UK mpg, 10.8 km/l) |
| Fuel consumption (economy) – combined | 12.8 l/100 km (18.4 US mpg, 22.1 UK mpg, 7.8 km/l) |
| CO2 emissions | 306 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 4.9 sec |
| Acceleration 0 – 62 mph | 4.9 sec |
| Acceleration 0 – 60 mph | 4.7 sec |
| Maximum speed | 310 km/h (192.63 mph) |
| Emission standard | Euro 4 |
| Weight-to-power ratio | 3.9 kg/Hp, 259.1 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 362.7 Nm/tonne |
| Power | 500 Hp @ 5500 rpm |
| Power per litre | 113.7 Hp/l |
| Torque | 700 Nm @ 4250 rpm (516.29 lb.-ft. @ 4250 rpm) |
| Engine layout | Front, Longitudinal |
| Engine displacement | 4398 cm3 (268.38 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 92 mm (3.62 in.) |
| Piston Stroke | 82.7 mm (3.26 in.) |
| Compression ratio | 9:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Supercharger, Intercooler |
| Valvetrain | DOHC |
| Kerb Weight | 1930 kg (4254.92 lbs.) |
| Max. weight | 2350 kg (5180.86 lbs.) |
| Max load | 420 kg (925.94 lbs.) |
| Trunk (boot) space – maximum | 450 l (15.89 cu. ft.) |
| Fuel tank capacity | 70 l (18.49 US gal, 15.4 UK gal) |
| Length | 4820 mm (189.76 in.) |
| Width | 1855 mm (73.03 in.) |
| Height | 1371 mm (53.98 in.) |
| Wheelbase | 2780 mm (109.45 in.) |
| Front track | 1558 mm (61.34 in.) |
| Rear (Back) track | 1598 mm (62.91 in.) |
| Minimum turning circle | 11.4 m (37.4 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, automatic transmission Switch-Tronic |
| Front suspension | Independent, type McPherson with coil spring and anti-roll bar |
| Rear suspension | Independent multi-link spring suspension with stabilizer |
| Front brakes | Ventilated discs |
| Rear brakes | Ventilated discs |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Hydraulic Steering |
| Tires size | Front wheel tires: 255/35 R20 Rear wheel tires: 285/30 R20 |
Powertrain & Engine Architecture
At the heart of the B6 Cabrio is Alpina’s modified version of the BMW N62 4.4-liter V8 engine. While based on the BMW unit, Alpina extensively reworked the engine, adding a mechanically driven supercharger. This supercharger, along with revised engine mapping, larger fuel injectors, and a high-flow exhaust system, boosted output to 500 horsepower and 516 lb-ft of torque. The engine utilizes a 9:1 compression ratio and a double-VANOS variable valve timing system for optimized performance across the rev range. The “Switch-Tronic” transmission is a ZF 6HP26 automatic, modified by Alpina to offer quicker shift times and a more responsive driving experience. It features a manual shift mode allowing the driver to select gears, enhancing driver engagement.
Driving Characteristics
The B6 Cabrio’s powertrain delivers a compelling blend of effortless power and refined cruising. The supercharger provides immediate throttle response, eliminating any turbo lag. Acceleration from 0 to 60 mph takes approximately 4.7 seconds, and the car can reach a top speed of 192.63 mph. The Switch-Tronic transmission is well-matched to the engine’s characteristics, providing smooth and decisive gear changes. Compared to the standard BMW 645Ci or 650i, the B6 offers significantly more power and a more aggressive driving experience. However, it retains a level of comfort and refinement that is characteristic of the grand touring segment. The gear ratios are tuned for both strong acceleration and relaxed highway cruising.
Equipment & Trim Levels
The B6 Cabrio was generously equipped as standard. Interior features included premium leather upholstery, wood trim, and Alpina-specific instrumentation. Standard equipment also included automatic climate control, a premium sound system, and power-adjustable seats. Optional extras included a navigation system, heated seats, and a variety of cosmetic enhancements. Alpina offered a bespoke customization program, allowing customers to personalize their vehicles with unique interior and exterior finishes. The interior featured Alpina badging and unique stitching patterns, setting it apart from standard BMW 6 Series models.
Chassis & Braking
The B6 Cabrio’s chassis was subtly modified to handle the increased power. Alpina fitted stiffer springs and dampers, along with larger stabilizer bars, to reduce body roll and improve handling. The braking system consisted of ventilated discs at all four corners, providing ample stopping power. The car also featured ABS (Anti-lock braking system) as standard. The suspension setup aimed to strike a balance between sporty handling and comfortable ride quality. The rear suspension utilized a multi-link design for improved stability and control.
Market Reception & Comparison
The Alpina B6 Cabrio was well-received by automotive critics, who praised its performance, refinement, and exclusivity. It was often seen as a more focused and engaging alternative to the standard BMW 6 Series convertible. Fuel economy, however, was a notable drawback, with combined fuel consumption of around 18.4 US mpg. Compared to the BMW 650i, the B6 offered more power and a more distinctive character, but at a higher price point. The B6 also offered a unique proposition compared to other high-performance convertibles of the time, such as the Porsche 911 Cabriolet, by prioritizing luxury and comfort alongside performance.
Legacy
The Alpina B6 Cabrio (E64) remains a sought-after vehicle among enthusiasts. The N62 engine, while known for some cooling system vulnerabilities, is generally considered reliable when properly maintained. The Switch-Tronic transmission has also proven to be durable. Today, these cars represent a unique blend of German engineering, performance, and exclusivity. Values have remained relatively stable, reflecting the car’s desirability and limited production numbers. The B6 Cabrio stands as a testament to Alpina’s ability to create compelling and distinctive automobiles that offer a unique driving experience.
