The Mercedes-Benz S-Class W221 S 550, produced from 2005 to 2009, represented a significant evolution in luxury and technology for the flagship Mercedes-Benz sedan. Positioned as a high-performance variant within the W221 range, the S 550 bridged the gap between the standard S-Class models and the ultra-luxury S 600. It offered a compelling combination of power, refinement, and advanced features, appealing to buyers seeking a sophisticated and capable grand tourer. The W221 generation itself was a major redesign, incorporating a host of new technologies including Pre-Safe brake assist and Active Body Control suspension.
Powertrain & Engine Architecture
The heart of the S 550 is the M273.961 5.5-liter naturally aspirated V8 engine. This engine, a cornerstone of Mercedes-Benz’s engineering prowess during the mid-2000s, produced 388 horsepower at 6000 rpm and 530 Nm (390.91 lb-ft) of torque at 2800 rpm. The engine utilizes a three-valve per cylinder (two intake, one exhaust) DOHC valvetrain and a multi-port fuel injection system. The cylinder bore measures 98 mm (3.86 in) and the piston stroke is 90.5 mm (3.56 in), resulting in a compression ratio of 10.7:1. The M273 engine is known for its smooth power delivery and relatively high specific output of 71 hp per liter.
Paired with the M273 engine is the 7G-TRONIC seven-speed automatic transmission. This transmission, a significant advancement over previous Mercedes-Benz automatics, offered smoother shifts, improved fuel efficiency, and a wider gear ratio spread. The 7G-TRONIC features a torque converter lock-up clutch that engages in multiple gears, further enhancing efficiency. The transmission’s gear ratios are tuned to balance acceleration and cruising comfort, providing responsive performance in a variety of driving conditions. Manual shift capability was also available via steering wheel-mounted paddle shifters or a gated shift lever.
Engine Code Specifics
The M273 engine family encompasses several variations, but the M273.961 specifically denotes the 5.5-liter configuration used in the S 550. This engine benefits from Mercedes-Benz’s ongoing development efforts, incorporating features like variable valve timing and a lightweight construction to optimize performance and efficiency. Regular maintenance, including oil changes with the specified lubricant (8.5 liters / 8.98 US qt) and coolant replacement (11.5 liters / 12.15 US qt), is crucial for maintaining the longevity of this engine.
Driving Characteristics
The S 550 delivers a driving experience characterized by effortless power and refined comfort. Acceleration from 0 to 100 km/h (0-62 mph) takes approximately 5.4 seconds, while 0-60 mph is achieved in around 5.1 seconds. The 7G-TRONIC transmission contributes to smooth and seamless gear changes, minimizing disruptions during acceleration. Compared to the base S-Class models with smaller engines, the S 550 offers a noticeably more responsive and engaging driving experience. However, it doesn’t possess the outright sporting character of the AMG-tuned S-Class variants. The engine’s torque curve provides ample power for overtaking maneuvers and maintaining high-speed cruising on the highway. The rear-wheel drive configuration provides a traditional luxury car feel, prioritizing comfort and stability over dynamic handling.
Equipment & Trim Levels
The S 550 came standard with a comprehensive array of luxury features. Interior appointments typically included premium leather upholstery, wood trim, and power-adjustable heated and ventilated front seats. Standard equipment also included a multi-function steering wheel, a premium audio system, automatic climate control, and a sunroof. The S 550 also benefited from Mercedes-Benz’s advanced safety technologies, including ABS, traction control, and a suite of airbags. Optional extras included features such as a rear seat entertainment system, massaging seats, a panoramic sunroof, and advanced driver-assistance systems like Distronic adaptive cruise control and lane-keeping assist. Trim levels were relatively limited, with most customization occurring through the selection of individual options.
Chassis & Braking
The W221 S-Class, including the S 550, utilized an advanced chassis design focused on ride comfort and handling stability. Both front and rear suspension systems employed air suspension, providing a smooth and controlled ride quality. The air suspension system automatically adjusts ride height and damping characteristics based on driving conditions and load. Braking duties were handled by ventilated discs on all four wheels, providing ample stopping power. The anti-lock braking system (ABS) and electronic stability program (ESP) further enhanced safety and control. The S 550’s curb weight of 1865 kg (4111.62 lbs) is substantial, but the powerful V8 engine and well-tuned chassis effectively manage the vehicle’s mass.
Market Reception & Comparison
The S 550 was generally well-received by automotive critics, who praised its powerful engine, refined ride quality, and luxurious interior. It was often compared favorably to its competitors, such as the BMW 750i and the Audi A8. Fuel economy, rated at 11.7 l/100 km (20.1 US mpg), was typical for a large luxury sedan of its era. Reliability was generally good, although some owners reported issues with the air suspension system and electronic components. Compared to the S 600 with its V12 engine, the S 550 offered a more accessible price point while still delivering a high level of performance and luxury. Compared to the smaller-engined S-Class models, the S 550 provided a significant upgrade in power and driving enjoyment.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | S-Class |
| Generation | S-Class (W221) |
| Type | S 550 (388 Hp) 7G-TRONIC |
| Start of production | 2005 |
| End of production | 2009 |
| Engine Type | Internal Combustion engine |
| Body type | Sedan |
| Seats | 5 |
| Doors | 4 |
| Fuel consumption (combined) | 11.7 l/100 km |
| Fuel consumption (US mpg) | 20.1 |
| Fuel consumption (UK mpg) | 24.1 |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0-100 km/h | 5.4 sec |
| Acceleration 0-62 mph | 5.4 sec |
| Acceleration 0-60 mph | 5.1 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Weight-to-power ratio | 4.8 kg/Hp |
| Power | 388 Hp @ 6000 rpm |
| Torque | 530 Nm @ 2800 rpm (390.91 lb.-ft. @ 2800 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | M 273.961 |
| Engine displacement | 5461 cm3 (333.25 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 98 mm (3.86 in.) |
| Piston Stroke | 90.5 mm (3.56 in.) |
| Compression ratio | 10.7:1 |
| Engine oil capacity | 8.5 l (8.98 US qt | 7.48 UK qt) |
| Coolant capacity | 11.5 l (12.15 US qt | 10.12 UK qt) |
| Kerb Weight | 1865 kg (4111.62 lbs.) |
| Max. weight | 2545 kg (5610.76 lbs.) |
| Trunk (boot) space | 560 l (19.78 cu. ft.) |
| Fuel tank capacity | 90 l (23.78 US gal | 19.8 UK gal) |
| Length | 5079 mm (199.96 in.) |
| Width | 1872 mm (73.7 in.) |
| Height | 1473 mm (57.99 in.) |
| Wheelbase | 3035 mm (119.49 in.) |
| Gearbox | 7 gears, automatic transmission G-TRONIC |
Legacy
The M273 engine, found in the S 550, has proven to be a relatively durable and reliable powerplant when properly maintained. While the air suspension system can be prone to issues as the vehicle ages, the engine itself is generally considered robust. On the used car market, the W221 S 550 represents a compelling value proposition for buyers seeking a luxurious and capable grand tourer at a more affordable price point than newer models. Its combination of performance, comfort, and advanced features continues to appeal to enthusiasts and discerning drivers alike. However, potential buyers should be aware of the potential maintenance costs associated with a vehicle of this age and complexity.
