The BMW 645Ci, produced from 2003 to 2005, represents a significant iteration of the E63 generation 6 Series. Positioned as a luxury coupe, it aimed to blend grand touring comfort with respectable performance. This variant, equipped with the N63B44 engine and a six-speed Steptronic automatic transmission, occupied a middle ground in the 6 Series lineup, offering a step up in power and refinement from the 630i while remaining more accessible than the range-topping 650i. The E63 6 Series was BMW’s attempt to recapture the spirit of the original 6 Series coupes of the 1970s and 80s, offering a more driver-focused alternative to the contemporary 7 Series sedan.
Technical Specifications
| Brand | BMW |
| Model | 6 Series |
| Generation | 6 Series (E63) |
| Type (Engine) | 645Ci (333 Hp) Steptronic |
| Start of production | 2003 |
| End of production | 2005 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Coupe |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 16.1 l/100 km (14.6 US mpg, 17.5 UK mpg, 6.2 km/l) |
| Fuel consumption (extra urban) | 8 l/100 km (29.4 US mpg, 35.3 UK mpg, 12.5 km/l) |
| Fuel consumption (combined) | 10.9 l/100 km (21.6 US mpg, 25.9 UK mpg, 9.2 km/l) |
| CO2 emissions | 264 g/km |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 5.8 sec |
| Acceleration 0 – 62 mph | 5.8 sec |
| Acceleration 0 – 60 mph | 5.5 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 4 |
| Weight-to-power ratio | 5.1 kg/Hp, 196.5 Hp/tonne |
| Weight-to-torque ratio | 3.8 kg/Nm, 265.5 Nm/tonne |
| Power | 333 Hp @ 6100 rpm |
| Power per litre | 75.7 Hp/l |
| Torque | 450 Nm @ 3600 rpm (331.9 lb.-ft. @ 3600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | N63B44 |
| 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 | 10:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | DOHC |
| Engine oil capacity | 8 l (8.45 US qt | 7.04 UK qt) |
| Coolant | 14.2 l (15 US qt | 12.49 UK qt) |
| Kerb Weight | 1695 kg (3736.84 lbs.) |
| Max. weight | 2065 kg (4552.55 lbs.) |
| Max load | 370 kg (815.71 lbs.) |
| Trunk (boot) space – minimum | 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 | 1373 mm (54.06 in.) |
| Wheelbase | 2780 mm (109.45 in.) |
| Front track | 1558 mm (61.34 in.) |
| Rear (Back) track | 1592 mm (62.68 in.) |
| Drag coefficient (Cd) | 0.29 |
| Minimum turning circle | 11.4 m (37.4 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears | 6 |
| Gearbox type | Automatic transmission |
| Front suspension | Coil spring |
| Rear suspension | Coil spring |
| Front brakes | Disc |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Hydraulic Steering |
| Tires size | 245/45 R18 |
| Wheel rims size | 8J X 18 |
Powertrain & Engine Architecture
The heart of the 645Ci is the N63B44, a 4.4-liter naturally aspirated V8 engine. This engine marked a departure from BMW’s previous V8 designs, utilizing aluminum construction and direct injection to improve efficiency and power output. The N63 featured Double-VANOS (variable valve timing) on both intake and exhaust camshafts, optimizing engine breathing across the rev range. The six-speed Steptronic automatic transmission, a common offering in BMWs of this era, provided smooth and relatively quick shifts. It featured adaptive shift programs, allowing the driver to select between more comfort-oriented or sportier shift patterns. While not as engaging as a manual transmission, the Steptronic offered a good balance of convenience and performance for grand touring applications.
Driving Characteristics
The 645Ci Automatic delivered a refined and capable driving experience. The 333 horsepower and 332 lb-ft of torque provided ample power for effortless cruising and brisk acceleration. The automatic transmission, while smooth, did introduce a slight disconnect compared to the more direct feel of a manual. The gear ratios were tuned for comfortable highway driving, with a focus on maximizing fuel economy at cruising speeds. Compared to the 630i, the 645Ci offered a noticeable performance boost, while the 650i, with its larger V8, provided even more exhilarating acceleration. The weight distribution, close to 50/50, contributed to balanced handling, though the car’s considerable weight (around 3737 lbs) was noticeable in tighter corners.
Equipment & Trim Levels
The 645Ci came standard with a generous array of features, befitting its luxury coupe status. These included leather upholstery, power-adjustable seats with memory function, automatic climate control, a premium sound system, and xenon headlights. Optional extras were plentiful, including a navigation system, sport seats, active steering, and a panoramic sunroof. Interior trim options ranged from wood veneers to aluminum accents, allowing buyers to personalize the cabin to their tastes. The standard dashboard configuration featured analog gauges with a central information display, providing information on vehicle status and settings.
Chassis & Braking
The E63 6 Series utilized a sophisticated chassis design, featuring a multi-link rear suspension and a MacPherson strut front suspension. This setup provided a comfortable ride while maintaining good handling characteristics. The 645Ci was equipped with disc brakes on all four wheels, providing ample stopping power. ABS (Anti-lock Braking System) was standard, enhancing safety in emergency braking situations. The steering was hydraulically assisted, offering precise and responsive control. The standard tire size was 245/45 R18, providing a good balance of grip and ride comfort.
Market Reception & Comparison
The 645Ci was generally well-received by automotive critics, who praised its stylish design, comfortable interior, and strong performance. However, some reviewers noted the car’s weight and the slightly detached feel of the automatic transmission. Compared to its rivals, such as the Mercedes-Benz CLK and the Porsche 911, the 645Ci offered a unique blend of luxury, performance, and practicality. Fuel economy was reasonable for a V8-powered coupe, averaging around 21.6 mpg in combined driving. Reliability was generally good, although some owners reported issues with the electronic systems and cooling system components.
Legacy
The E63 645Ci remains a desirable used car today, particularly among BMW enthusiasts. The N63B44 engine, while complex, is generally considered reliable if properly maintained. Common maintenance items include regular oil changes, coolant flushes, and inspection of the cooling system components. The Steptronic automatic transmission is also relatively durable, but may require servicing at higher mileages. The E63 6 Series represents a significant chapter in BMW’s history, showcasing the brand’s commitment to blending luxury, performance, and technology. Its timeless design and engaging driving experience continue to appeal to drivers seeking a sophisticated and rewarding grand touring experience.
