The Alpina B4 Cabrio 6.0 (410 Hp) Switch-Tronic, produced between 2014 and 2017, represents a high-performance iteration of the BMW F32 4 Series Convertible. Alpina, a renowned German automotive engineering company, took the already capable BMW platform and elevated it with significant engine, suspension, and aesthetic enhancements. This model occupied the top echelon of the 4 Series Cabriolet range, positioned above all standard BMW offerings and competing with other high-end performance convertibles. It was primarily marketed in Europe and select international markets, offering a unique blend of luxury, performance, and exclusivity.
Technical Specifications
| Brand | Alpina |
| Model | B4 |
| Generation | B4 Cabrio |
| Type (Engine) | 6.0 (410 Hp) Switch-Tronic |
| Start of production | 2014 |
| End of production | 2017 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (economy) – urban | 10.8 l/100 km (21.8 US mpg, 26.2 UK mpg, 9.3 km/l) |
| Fuel consumption (economy) – extra urban | 6.4 l/100 km (36.8 US mpg, 44.1 UK mpg, 15.6 km/l) |
| Fuel consumption (economy) – combined | 8 l/100 km (29.4 US mpg, 35.3 UK mpg, 12.5 km/l) |
| CO2 emissions | 186 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 4.5 sec |
| Acceleration 0 – 62 mph | 4.5 sec |
| Acceleration 0 – 60 mph | 4.3 sec |
| Maximum speed | 301 km/h (187.03 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 4.5 kg/Hp, 222.8 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 326.1 Nm/tonne |
| Power | 410 Hp @ 5500-6250 rpm |
| Power per litre | 137.6 Hp/l |
| Torque | 600 Nm @ 3000-4000 rpm (442.54 lb.-ft. @ 3000-4000 rpm) |
| Engine layout | Front, Longitudinal |
| Engine displacement | 2979 cm3 (181.79 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 84 mm (3.31 in.) |
| Piston Stroke | 89.6 mm (3.53 in.) |
| Compression ratio | 10.2:1 |
| Fuel injection system | Direct injection |
| Engine aspiration | BiTurbo, Intercooler |
| Kerb Weight | 1840 kg (4056.51 lbs.) |
| Max. weight | 2300 kg (5070.63 lbs.) |
| Max load | 460 kg (1014.13 lbs.) |
| Trunk (boot) space – minimum | 220 l (7.77 cu. ft.) |
| Trunk (boot) space – maximum | 370 l (13.07 cu. ft.) |
| Fuel tank capacity | 60 l (15.85 US gal, 13.2 UK gal) |
| Permitted trailer load with brakes (12%) | 1700 kg (3747.86 lbs.) |
| Permitted trailer load without brakes | 750 kg (1653.47 lbs.) |
| Length | 4640 mm (182.68 in.) |
| Width | 1825 mm (71.85 in.) |
| Height | 1380 mm (54.33 in.) |
| Wheelbase | 2810 mm (110.63 in.) |
| Front track | 1552 mm (61.1 in.) |
| Rear (Back) track | 1576 mm (62.05 in.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 8 gears, automatic transmission Switch-Tronic |
| Front brakes | Ventilated discs |
| Rear brakes | Ventilated discs |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 245/30 ZR20; 265/30 ZR20 |
| Wheel rims size | 8J x 20; 9J x 20 |
INTRODUCTION
The Alpina B4 Cabrio 6.0 Switch-Tronic is a performance-oriented convertible based on the BMW F32 4 Series. Produced from 2014 to 2017, it represents Alpina’s expertise in refining and enhancing existing BMW models. Unlike a full model replacement, Alpina takes existing BMW platforms and significantly upgrades them, focusing on powertrain, suspension, and interior appointments. The “6.0” designation refers to the engine displacement, and the “Switch-Tronic” denotes the specific 8-speed automatic transmission with Alpina’s unique shift programming. This car aimed to deliver a more engaging and luxurious driving experience than the standard 4 Series convertibles, appealing to buyers seeking a blend of performance and open-air motoring.
Powertrain & Engine Architecture
At the heart of the B4 Cabrio 6.0 lies a heavily modified version of BMW’s N55 inline-six engine. Alpina increased the displacement from 3.0 liters to 3.0 liters, employing forged pistons, a revised crankshaft, and larger turbochargers. The engine utilizes direct fuel injection and twin-turbocharging with an intercooler to produce 410 horsepower at 5500-6250 rpm and 600 Nm (442.54 lb-ft) of torque between 3000-4000 rpm. The engine code is specific to Alpina’s modifications and differs from standard BMW N55 variants. The Switch-Tronic 8-speed automatic transmission is a ZF unit, but Alpina recalibrated the shift points and added a “Drive Select” system offering Comfort, Sport, and Manual modes. This allows drivers to tailor the transmission’s behavior to their preferences. The transmission is designed for smooth, yet rapid shifts, enhancing both comfort and performance.
Driving Characteristics
The B4 Cabrio 6.0 delivers a noticeably different driving experience compared to standard 4 Series convertibles. The increased power and torque, combined with the optimized transmission, result in brisk acceleration – 0 to 60 mph in approximately 4.3 seconds and a top speed of 187 mph. The Alpina-tuned suspension, featuring stiffer springs and dampers, reduces body roll and improves handling. While not as track-focused as some dedicated sports cars, the B4 Cabrio offers a confident and engaging driving experience on winding roads. The Switch-Tronic transmission provides quick and precise shifts in Sport mode, while Comfort mode prioritizes smoothness and fuel efficiency. Compared to the 435i convertible, the B4 Cabrio offers significantly more power and a more refined driving experience. The higher output versions, like the M4 convertible, offer even more aggressive performance, but at the expense of some ride comfort.
Equipment & Trim Levels
The Alpina B4 Cabrio 6.0 came exceptionally well-equipped as standard. Interior features included Lavalina leather upholstery, Alpina-specific interior trim (often featuring wood or carbon fiber), sport seats with adjustable bolstering, and a premium sound system. Standard exterior features included Alpina’s signature aerodynamic body kit, including a front spoiler, side skirts, and a rear diffuser. Optional extras included a panoramic sunroof, upgraded leather options, and various driver-assistance systems. The interior was designed to be both luxurious and sporty, reflecting Alpina’s commitment to providing a high-end driving experience. The overall aesthetic was more understated and elegant than the more aggressive styling of the BMW M4.
Chassis & Braking
The B4 Cabrio retained the BMW 4 Series’ chassis layout, featuring a MacPherson strut front suspension and a multi-link rear suspension. However, Alpina made significant modifications to the suspension components, including stiffer springs, dampers, and stabilizer bars. This resulted in reduced body roll and improved handling. The braking system consisted of ventilated discs at all four corners, providing ample stopping power. ABS (Anti-lock Braking System) was standard. The car’s weight distribution was optimized for balanced handling, contributing to its confident cornering ability. The standard tire size was 245/30 ZR20 at the front and 265/30 ZR20 at the rear, providing excellent grip.
Market Reception & Comparison
The Alpina B4 Cabrio 6.0 was generally well-received by automotive critics. Reviewers praised its powerful engine, refined driving experience, and luxurious interior. It was often positioned as a compelling alternative to the BMW M4 Convertible, offering a more comfortable ride and a more understated aesthetic. Fuel economy was respectable for a high-performance convertible, with combined figures around 29.4 US mpg. Reliability was generally good, benefiting from Alpina’s meticulous engineering and BMW’s robust mechanical components. However, the B4 Cabrio’s higher price tag compared to the standard 4 Series convertibles limited its appeal to a niche market of discerning buyers.
Legacy
The Alpina B4 Cabrio 6.0 remains a desirable and relatively rare vehicle in the used car market. The N55 engine, while not the latest generation, is known for its durability and tunability. Regular maintenance, including oil changes and inspections of the turbochargers, is crucial for long-term reliability. The Switch-Tronic transmission is generally reliable, but proper fluid changes are essential. Today, these cars are sought after by enthusiasts who appreciate their unique blend of performance, luxury, and exclusivity. The B4 Cabrio 6.0 represents a high point in Alpina’s history, showcasing the company’s ability to create truly special and engaging automobiles.
