The Mercedes-Benz SL (R107) 420 SL CAT, produced from July 1985 to August 1989, represents a refined iteration of the iconic R107 roadster. This variant, equipped with the M116 E 42 V8 engine and a four-speed automatic transmission, occupied a premium position within the R107 lineup, offering a blend of performance, luxury, and sophisticated engineering. The “CAT” designation refers to the catalytic converter, indicating compliance with evolving emissions standards. The R107 platform, spanning from 1971 to 1989, was a significant success for Mercedes-Benz, known for its robust construction and timeless design.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | SL |
| Generation | SL (R107, facelift 1985) |
| Type (Engine) | 420 SL CAT V8 (204 Hp) Automatic |
| Start of production | July, 1985 |
| End of production | August, 1989 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Roadster |
| Seats | 2 |
| Doors | 2 |
| Fuel consumption (urban) | 15.4 l/100 km (15.3 US mpg, 18.3 UK mpg, 6.5 km/l) |
| Fuel consumption (extra urban) | 9.9 l/100 km (23.8 US mpg, 28.5 UK mpg, 10.1 km/l) |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 9 sec |
| Acceleration 0 – 62 mph | 9 sec |
| Acceleration 0 – 60 mph | 8.6 sec |
| Maximum speed | 205 km/h (127.38 mph) |
| Weight-to-power ratio | 7.8 kg/Hp, 127.5 Hp/tonne |
| Weight-to-torque ratio | 5.3 kg/Nm, 190 Nm/tonne |
| Power | 204 Hp @ 5200 rpm |
| Power per litre | 48.6 Hp/l |
| Torque | 304 Nm @ 3600 rpm (224.22 lb.-ft. @ 3600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | M 116 E 42 / 116.964 |
| Engine displacement | 4196 cm3 (256.06 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 92 mm (3.62 in.) |
| Piston Stroke | 78.9 mm (3.11 in.) |
| Compression ratio | 9:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | SOHC |
| Engine oil capacity | 8 l (8.45 US qt | 7.04 UK qt) |
| Coolant capacity | 12.5 l (13.21 US qt | 11 UK qt) |
| Kerb Weight | 1600 kg (3527.4 lbs.) |
| Max. weight | 2020 kg (4453.34 lbs.) |
| Max load | 420 kg (925.94 lbs.) |
| Fuel tank capacity | 85 l (22.45 US gal | 18.7 UK gal) |
| Length | 4390 mm (172.83 in.) |
| Width | 1790 mm (70.47 in.) |
| Height | 1307 mm (51.46 in.) |
| Wheelbase | 2455 mm (96.65 in.) |
| Front track | 1465 mm (57.68 in.) |
| Rear track | 1466 mm (57.72 in.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears | 4 |
| Gearbox type | Automatic transmission |
| Front suspension | Double wishbone |
| Rear suspension | Threaded twist beam |
| Front brakes | Ventilated discs |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Power steering | Hydraulic Steering |
| Tires size | 205/65 R15 |
| Wheel rims size | 7J x 15 |
INTRODUCTION
The 420 SL CAT built upon the success of the R107 series, offering a more powerful and refined experience than its smaller-engined siblings. Introduced as part of the facelifted R107 range in 1985, it featured subtle cosmetic updates and, crucially, the introduction of catalytic converters to meet increasingly stringent emissions regulations in many markets. Positioned as a luxury grand tourer, the 420 SL aimed to provide comfortable long-distance cruising with ample power for spirited driving. It was a popular choice for buyers seeking a sophisticated and reliable open-top vehicle.
Powertrain & Engine Architecture
At the heart of the 420 SL CAT lies the M116 E 42 V8 engine, a 4.2-liter naturally aspirated powerplant. This engine, a cornerstone of Mercedes-Benz’s engineering prowess, featured a cast-iron block and aluminum cylinder heads. It employed a single overhead camshaft (SOHC) design with two valves per cylinder. Fuel delivery was managed by a Bosch K-Jetronic multi-port fuel injection system, known for its reliability and precise metering. The engine produced 204 horsepower at 5200 rpm and 304 Nm (224.22 lb-ft) of torque at 3600 rpm. The four-speed automatic transmission, a robust unit designed to handle the V8’s output, provided smooth and relatively quick shifts. This transmission was not known for its sportiness, prioritizing comfort and refinement over aggressive gear changes.
Driving Characteristics
The 420 SL Automatic offered a distinctly different driving experience compared to the manual transmission versions or the smaller-engined models. While not as overtly sporty, the automatic transmission provided effortless cruising and made the car exceptionally easy to drive in urban environments. Acceleration from 0-60 mph took approximately 8.6 seconds, and it could reach a top speed of 205 km/h (127.38 mph). The automatic’s gear ratios were geared towards relaxed highway driving, with a focus on maintaining comfortable engine speeds. Compared to the 380 SL, the 420 SL offered a noticeable increase in power and torque, resulting in more confident overtaking and a more relaxed feel when carrying passengers or luggage. However, it lacked the direct engagement and responsiveness of the manual gearbox.
Equipment & Trim Levels
The 420 SL CAT came well-equipped as standard, reflecting its premium positioning. Interior features typically included leather upholstery, power windows, central locking, and a high-quality sound system. Air conditioning was standard, essential for comfortable open-top motoring. Optional extras included a sunroof, heated seats, and upgraded audio systems. The dashboard layout was typical of Mercedes-Benz in the 1980s, featuring wood trim and a clear, functional instrument cluster. The quality of materials and build was exceptionally high, contributing to the car’s enduring appeal.
Chassis & Braking
The R107 chassis featured independent suspension all around, with double wishbones at the front and a threaded twist beam rear axle. This setup provided a comfortable ride and predictable handling. The 420 SL was equipped with ventilated disc brakes at the front and solid discs at the rear. An Anti-lock Braking System (ABS) was standard, enhancing safety and stability during hard braking. The steering was a recirculating ball system with hydraulic power assistance, providing a relatively light and precise feel. The suspension was tuned for comfort rather than outright sportiness, prioritizing a smooth ride over aggressive cornering.
Market Reception & Comparison
The 420 SL CAT was generally well-received by automotive critics. It was praised for its comfortable ride, refined engine, and luxurious interior. However, some critics noted that the automatic transmission could feel somewhat sluggish compared to manual options. Compared to the 380 SL, the 420 SL offered a significant performance upgrade, but at a higher price point. The 420 SL also offered better fuel economy than the larger 560 SL, making it a more practical choice for some buyers. Reliability was generally excellent, although maintenance costs could be substantial due to the complexity of the engine and the car’s overall sophistication.
Legacy
The Mercedes-Benz R107 420 SL CAT remains a highly sought-after classic car today. The M116 V8 engine is known for its durability and longevity, provided it has been properly maintained. While parts availability can be a concern, a dedicated network of specialists and suppliers exists to support R107 owners. The 420 SL CAT represents a sweet spot in the R107 range, offering a compelling combination of performance, luxury, and reliability. Its timeless design and enduring appeal ensure its continued popularity among collectors and enthusiasts. Well-maintained examples command strong prices in the used car market, reflecting their status as a desirable and iconic vehicle.
