The Alpina B4 Cabrio (facelift 2017) S 3.0, equipped with the Switch-Tronic 8-speed automatic transmission, represents a high-performance iteration of the BMW 4 Series Convertible. Produced from 2017 to 2019, this model occupied the top echelon of the B4 Cabrio range, offering a significant step up in power and refinement compared to the standard 4 Series and even the lower-tier Alpina variants. It was positioned as a luxurious, open-top grand tourer, blending exhilarating performance with the exclusivity and bespoke craftsmanship synonymous with the Alpina brand. The facelift brought subtle styling updates and further refinement to an already compelling package.
Technical Specifications
| Brand | Alpina |
| Model | B4 |
| Generation | B4 Cabrio (facelift 2017) |
| Type (Engine) | S 3.0 (440 Hp) Switch-Tronic |
| Start of production | 2017 |
| End of production | 2019 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (economy) – urban | 11.1 l/100 km (21.2 US mpg) |
| Fuel consumption (economy) – extra urban | 6.7 l/100 km (35.1 US mpg) |
| Fuel consumption (economy) – combined | 8.3 l/100 km (28.3 US mpg) |
| CO2 emissions | 190 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 4.3 sec |
| Acceleration 0 – 62 mph | 4.3 sec |
| Acceleration 0 – 60 mph | 4.1 sec |
| Maximum speed | 304 km/h (188.9 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 4.4 kg/Hp |
| Weight-to-torque ratio | 2.9 kg/Nm |
| Power | 440 Hp @ 5500-6250 rpm |
| Power per litre | 147.7 Hp/l |
| Torque | 660 Nm @ 3000-4500 rpm (486.79 lb.-ft.) |
| 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 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Direct injection |
| Engine aspiration | BiTurbo, Intercooler |
| Kerb Weight | 1915 kg (4221.85 lbs.) |
| Max. weight | 2300 kg (5070.63 lbs.) |
| Max load | 385 kg (848.78 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 | Rear wheel drive |
| 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 |
Powertrain & Engine Architecture
At the heart of the B4 Cabrio S 3.0 lies Alpina’s meticulously engineered version of the BMW N55 inline-six engine. While based on the BMW unit, Alpina extensively modified it with bespoke pistons, connecting rods, and a reinforced crankshaft. The engine utilizes twin turbochargers with intercooling, delivering 440 horsepower at 5500-6250 rpm and a substantial 660 Nm (486.79 lb-ft) of torque between 3000 and 4500 rpm. Direct fuel injection ensures precise fuel delivery, optimizing both performance and efficiency. The engine’s character is distinctly Alpina – a broad, flat torque curve providing effortless acceleration in any gear. The Switch-Tronic 8-speed automatic transmission, a ZF unit, is specifically calibrated for Alpina’s requirements. It offers both fully automatic operation and manual gear selection via steering wheel-mounted paddles, providing the driver with a degree of control. The transmission’s programming prioritizes smooth shifts and responsive downchanges.
Driving Characteristics
The B4 Cabrio S 3.0 delivers a refined yet potent driving experience. The combination of the high-output engine and the quick-shifting Switch-Tronic transmission results in a 0-60 mph time of approximately 4.1 seconds and a top speed of 188.9 mph. Unlike some high-performance convertibles, the B4 Cabrio doesn’t suffer from significant chassis flex, maintaining a composed feel even during spirited driving. The automatic transmission, while incredibly capable, doesn’t quite match the immediacy of a dual-clutch gearbox, but it offers a level of smoothness and refinement that many drivers will appreciate. The gear ratios are tuned for both acceleration and comfortable cruising, making it an excellent grand tourer. Compared to the standard 4 Series Convertible, the Alpina offers a noticeably more powerful and responsive driving experience. Against other Alpina B4 variants, such as those with the diesel engine, the S 3.0 provides a more traditional, high-revving petrol experience.
Equipment & Trim Levels
The B4 Cabrio S 3.0 came generously equipped as standard. Interior appointments included Lavalina leather upholstery, Alpina-specific interior trim (often featuring wood or carbon fiber), and sport seats with adjustable bolstering. Standard features also included a premium sound system, navigation, climate control, and a host of driver-assistance systems. Optional extras included upgraded leather packages, a head-up display, and various customization options through Alpina’s bespoke program. The exterior featured Alpina-specific aerodynamic enhancements, including a front spoiler, rear diffuser, and unique alloy wheels. The interior trim was designed to convey a sense of luxury and exclusivity, setting it apart from the standard BMW 4 Series.
Chassis & Braking
The B4 Cabrio’s chassis builds upon the BMW 4 Series Convertible platform, but with Alpina-specific modifications. The suspension features stiffer springs and dampers, along with revised anti-roll bars, to improve handling and reduce body roll. The braking system utilizes ventilated discs all around, providing ample stopping power. ABS (Anti-lock Braking System) is standard. The steering is a rack-and-pinion system with electric power assistance, offering precise and responsive control. The car rides on staggered 20-inch alloy wheels, with wider tires at the rear to enhance traction.
Market Reception & Comparison
The Alpina B4 Cabrio S 3.0 was generally well-received by automotive critics. It was praised for its blend of performance, luxury, and exclusivity. Reviewers noted the powerful engine, refined transmission, and comfortable ride. Fuel economy, while not exceptional, was considered reasonable for a high-performance convertible. Compared to other high-performance convertibles in its price range, the B4 Cabrio offered a unique proposition – a blend of German engineering, bespoke craftsmanship, and a relatively understated aesthetic. Reliability was generally good, benefiting from the robust BMW underpinnings and Alpina’s meticulous engineering.
Legacy
The Alpina B4 Cabrio (facelift 2017) S 3.0 remains a desirable used car today. The N55 engine, while not the newest powerplant, is known for its durability and tunability. The Switch-Tronic transmission is also generally reliable. However, as with any high-performance vehicle, regular maintenance is crucial. Values have remained relatively stable, reflecting the car’s exclusivity and desirability. It represents a compelling option for buyers seeking a high-performance, open-top grand tourer with a touch of understated elegance.
