The BMW 8 Series Convertible (G14) 840d, produced from November 2020 to March 2022, represents a blend of luxury grand touring and modern diesel technology. Positioned as a mid-range offering within the G14 8 Series Convertible lineup, it slots between the entry-level 840i and the high-performance M8 Competition. This variant aimed to provide a refined driving experience with strong torque and improved fuel efficiency compared to its gasoline-powered sibling, while still delivering the open-air enjoyment expected of a convertible. The 840d utilizes a mild-hybrid system to further enhance efficiency and smoothness.
Technical Specifications
| Brand | BMW |
| Model | 8 Series |
| Generation | 8 Series Convertible (G14) |
| Type (Engine) | 840d (340 Hp) Mild Hybrid xDrive Steptronic |
| Start of production | November, 2020 |
| End of production | March, 2022 |
| Powertrain Architecture | MHEV (Mild Hybrid Electric Vehicle) |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 7.3-7.5 l/100 km (32.2-31.4 US mpg) |
| Fuel consumption (extra urban) | 4.9-5.2 l/100 km (48-45.2 US mpg) |
| Fuel consumption (combined) | 5.7-6.0 l/100 km (41.3-39.2 US mpg) |
| CO2 emissions | 151-159 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 5.1 sec |
| Acceleration 0 – 62 mph | 5.1 sec |
| Acceleration 0 – 60 mph | 4.8 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 6d |
| Weight-to-power ratio | 6 kg/Hp |
| Weight-to-torque ratio | 2.9 kg/Nm |
| Electric motor power | 11 Hp |
| Power | 340 Hp @ 4400 rpm |
| Torque | 700 Nm @ 1750-2250 rpm (516.29 lb.-ft.) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | B57D30B |
| Engine displacement | 2993 cm3 (182.64 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 84 mm (3.31 in.) |
| Piston Stroke | 90 mm (3.54 in.) |
| Compression ratio | 16.5:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Twin-power turbo, Intercooler |
| Engine oil capacity | 7 l (7.4 US qt | 6.16 UK qt) |
| Coolant capacity | 10.2 l (10.78 US qt | 8.97 UK qt) |
| Kerb Weight | 2030 kg (4475.38 lbs.) |
| Max. weight | 2500 kg (5511.56 lbs.) |
| Max load | 470 kg (1036.17 lbs.) |
| Trunk (boot) space (minimum) | 350 l (12.36 cu. ft.) |
| Fuel tank capacity | 66 l (17.44 US gal | 14.52 UK gal) |
| Length | 4843 mm (190.67 in.) |
| Width | 1902 mm (74.88 in.) |
| Height | 1339 mm (52.72 in.) |
| Wheelbase | 2822 mm (111.1 in.) |
| Front track | 1627 mm (64.06 in.) |
| Rear track | 1642 mm (64.65 in.) |
| Ride height (ground clearance) | 118 mm (4.65 in.) |
| Drag coefficient (Cd) | 0.30 |
| Minimum turning circle | 11.9 m (39.04 ft.) |
| Drivetrain Architecture | All wheel drive (4×4), MHEV |
| Number of gears | 8 |
| Gearbox type | Automatic transmission Steptronic |
| Front suspension | Double wishbone |
| Rear suspension | Independent multi-link suspension |
| Front brakes | Ventilated discs |
| Rear brakes | Ventilated discs |
| Steering type | Steering rack and pinion |
| Power steering | Electric |
| Front tires | 245/45 R18 100Y XL |
| Rear tires | 275/40 R18 103Y XL |
| Front wheel rims | 8J x 18 |
| Rear wheel rims | 9J x 18 |
Powertrain & Engine Architecture
The heart of the 840d is BMW’s B57D30B 3.0-liter inline-six diesel engine. This engine is a member of the modular BMW engine family, known for its robust construction and efficiency. The B57 utilizes a sophisticated diesel commonrail fuel injection system, delivering fuel at extremely high pressures for optimized combustion. A twin-turbocharger setup, incorporating both a low-pressure and a high-pressure turbo, provides broad torque across the rev range. The intercooler helps to cool the intake air, further enhancing performance. The mild-hybrid system, consisting of a 48V starter-generator, provides a power boost during acceleration and allows for smoother start-stop operation, contributing to improved fuel economy. The engine is longitudinally mounted, driving all four wheels through BMW’s xDrive all-wheel-drive system.
Driving Characteristics
The 840d offers a distinctly different driving experience compared to the 840i gasoline variant. While lacking the outright top-end power of the gasoline engine, the 840d compensates with a substantial 516 lb-ft of torque available from just 1750 rpm. This results in effortless acceleration and strong in-gear performance, making it ideal for long-distance cruising. The eight-speed Steptronic automatic transmission is well-tuned, providing smooth and quick shifts. While not as sporty as the transmission in the M8 Competition, it offers a comfortable and refined driving experience. The xDrive system provides excellent traction in all weather conditions, enhancing stability and confidence. Compared to manual transmission versions (not commonly offered on this model), the automatic prioritizes ease of use and comfort over driver engagement.
Equipment & Trim Levels
The 840d Convertible came standard with a high level of equipment, befitting its luxury positioning. Standard features included leather upholstery, power-adjustable seats with memory function, a premium sound system, a large infotainment display with iDrive controller, and a comprehensive suite of safety features. Optional extras included upgraded leather options, a head-up display, active roll stabilization, and various driver-assistance systems. Interior trim options ranged from elegant wood veneers to modern aluminum accents. The convertible top was a fully automatic soft top, available in several colors.
Chassis & Braking
The G14 8 Series Convertible features a sophisticated chassis designed for both comfort and handling. The front suspension utilizes a double-wishbone setup, while the rear employs an independent multi-link suspension. This configuration provides a good balance between ride quality and cornering stability. The 840d is equipped with ventilated disc brakes on all four wheels, providing ample stopping power. ABS (Anti-lock Braking System) and electronic stability control are standard features. The steering is electrically assisted, offering precise and responsive control.
Market Reception & Comparison
The 840d Convertible was generally well-received by automotive critics. It was praised for its refined driving experience, strong torque, and improved fuel economy compared to the 840i. However, some critics noted that it lacked the outright excitement of the higher-performance M8 Competition. Compared to the 840i, the 840d offered a more relaxed and efficient driving experience, appealing to buyers who prioritized comfort and long-distance cruising. Its fuel economy figures were significantly better than the gasoline variant, making it a more practical choice for those covering high mileage. Reliability reports have been generally positive, with the B57 engine proving to be a durable and dependable unit.
Legacy
The BMW 8 Series Convertible (G14) 840d represents a compelling combination of luxury, performance, and efficiency. The B57 engine has established a reputation for long-term reliability, and well-maintained examples are likely to remain desirable on the used car market. The mild-hybrid technology, while relatively early in its development, demonstrates BMW’s commitment to improving fuel economy and reducing emissions. The G14 8 Series Convertible, and specifically the 840d variant, continues to be appreciated for its elegant styling, refined driving experience, and overall quality.
