19/07/2026
The Mercedes-Benz M117 V8 petrol engine is a legendary powerplant that powered some of the most iconic Mercedes-Benz vehicles from 1971 through 1992. Known for its robust construction, smooth operation, and respectable performance, the M117 served as the heart of models like the 350, 450, 500, and 560 series across various chassis. This article delves into the technical specifications, variations, and unique aspects of the M117 engine, providing a comprehensive overview for enthusiasts and owners alike.
Understanding the M117 V8
The M117 engine family was developed as a premium V8 offering from Mercedes-Benz, designed to provide substantial power and torque for their luxury and performance cars. It featured an overhead cam (OHC) design with two valves per cylinder as standard across most of its production run. Fuel delivery was managed by either the sophisticated D-Jetronic or the widely adopted K-Jetronic (and later KE-Jetronic) fuel injection systems, depending on the specific application and year of manufacture.
Displacement and Key Models
The M117 was produced in several base displacements, each catering to different performance and market demands:
| Displacement (Litres) | Displacement (cc) | Common Model Designations | Approximate Production Years |
|---|---|---|---|
| 4.5 L | 4,520 cc | M117.982 (D-Jetronic), M117.985 (K-Jetronic) | 1971-1980 |
| 5.0 L | 4,973 cc | M117.963, M117.965 | 1979-1991 |
| 5.0 L | 5,025 cc | (Less common variant, often associated with specific AMG modifications) | N/A (Specific to performance tuning) |
| 5.6 L | 5,547 cc | M117.968 | 1985-1991 |
Technical Data and Specifications
The M117 engine's specifications varied significantly across its different variants. Here's a look at some key technical data:
M117 4.5 Litre (450)
The 4.5-litre M117 was one of the earliest and most widespread versions. It came in two primary fuel injection forms:
- M117.982 (D-Jetronic): Introduced around 1971-1975, this variant typically featured a compression ratio of 8.8:1. With a bore of 92 mm and a stroke of 85 mm, it produced approximately 224 PS (165 kW; 221 hp) at 5000 rpm and 378 Nm (279 ft/lb) of torque at 3000 rpm. This engine powered models like the 450SL (R107) and 450SLC (C107) in its early years, and also found its way into the W116 S-Class (450SE/SEL) and even earlier models like the W108 (280SE 4.5) and W109 (300SEL 4.5).
- M117.985 (K-Jetronic): Produced from 1973-1980, this version also used a 92 mm bore and 85 mm stroke with an 8.8:1 compression ratio. However, with the K-Jetronic system, output was typically around 218 PS (160 kW) at 5000 rpm and 360 Nm (266 ft/lb) of torque at 3250 rpm. This engine was prevalent in later 450SL and 450SLC models and also featured in the W126 S-Class (380SE/SEL/SEC) after its displacement was slightly reduced.
It's important to note that European and US market versions often had different power outputs due to emissions regulations and fuel quality differences.
M117 5.0 Litre (500)
The 5.0-litre M117 represented an increase in displacement and performance. Key variants include:
- M117.963: Introduced in the 450 SLC 5.0 around May 1979, this engine featured a 96.5 mm bore and 85 mm stroke, with a compression ratio of 9.2:1. It produced around 231 PS (170 kW; 228 hp) at 5200 rpm and 405 Nm (299 ft/lb) of torque at 3750 rpm.
- M117.965 (KE-Jetronic): Produced from 1979 to 1991, this was a highly successful variant powering the 500SE/SEL/SEC (W126/C126) and 500SL/SLC (R107/C107). With a 10:1 compression ratio and the same bore/stroke as the .963, it delivered a more potent 265 PS (195 kW) at 5200 rpm and 405 Nm (299 ft/lb) of torque at 4000 rpm. Significant updates occurred in the late 1980s, with modifications impacting compression, power, and torque figures for different market applications (ECE, KAT/USA, RÜF).
M117 5.6 Litre (560)
The largest displacement M117, the 5.6-litre (5547 cc), was primarily designated as the M117.968. This engine was most famously used in the 560SL (R107) and 560SEL/SEC (W126/C126) models from 1985 to 1991. It featured a bore of 96.5 mm and an increased stroke of 94.8 mm. With a 10:1 compression ratio, it produced around 299 PS (220 kW) at 5200 rpm and 455 Nm (336 ft/lb) of torque at 3750 rpm for European (ECE/RÜF) versions. US market (KAT) versions often had lower compression (9.0:1) and consequently reduced power output (e.g., 238 hp / 170 kW).
The Rare AMG M117 Evolution
While the standard M117 engines were already potent, Mercedes-AMG took things to another level. In select high-performance special application vehicles, AMG developed significantly enhanced versions of the M117. These included:
- 32-Valve DOHC Engines: AMG created versions with a quad-cam, four-valve per cylinder configuration, dramatically increasing breathing efficiency and power potential. These engines often displaced 5.0, 5.4, 5.6, or even 6.0 litres.
- AMG 560 SEC 6.0 "Wide-Body": One of the most famous examples is the AMG 560 SEC 6.0. These modified M117 engines, boosted to 6.0 litres and featuring the 32-valve DOHC setup, produced substantially more torque at lower RPMs than their standard counterparts, offering truly supercar-like performance. Some of these AMG-tuned M117 variants could produce over twice the torque of unmodified models.
These AMG versions represent the pinnacle of M117 development, showcasing the inherent potential of the V8 architecture when pushed to its limits.
Fuel Injection Systems: D-Jetronic vs. K-Jetronic
The transition from D-Jetronic to K-Jetronic (and later KE-Jetronic) marked significant advancements in fuel delivery:
| Feature | D-Jetronic | K-Jetronic | KE-Jetronic |
|---|---|---|---|
| Type | Electronic Fuel Injection (EFI) | Continuous Mechanical Fuel Injection (MFI) | Electronic-Controlled Mechanical Fuel Injection |
| Control | ECU controlled based on sensor inputs (MAP, RPM, Temp, etc.) | Mechanically controlled by airflow sensor plate and fuel distributor. No ECU for fuel control. | Combines mechanical fuel delivery with electronic control for ignition timing and idle speed, with some versions incorporating lambda feedback. |
| Complexity | More complex, requires ECU and sensors. | Simpler, more robust mechanical system. | More complex than K-Jetronic, incorporates electronic elements. |
| Typical Use (M117) | Early 4.5L models (e.g., M117.982) | Later 4.5L, 5.0L, and 5.6L models (e.g., M117.985, M117.965, M117.968) | Later 5.0L and 5.6L models, often with lambda control. |
The D-Jetronic system offered precise fuel control but was more susceptible to electronic failures. K-Jetronic, while purely mechanical, was renowned for its reliability and durability, making it a favourite for many tuners. KE-Jetronic offered a bridge, retaining the mechanical core but adding electronic oversight for improved efficiency and emissions.
Maintenance and Common Issues
The M117 engine is generally considered a very durable and long-lasting engine, provided it has been maintained correctly. Key maintenance points include:
- Regular Oil Changes: Using the correct grade of oil is crucial for longevity.
- Ignition System: Spark plugs, distributor cap, rotor, and ignition wires need regular inspection and replacement.
- Fuel System: Fuel filters, injectors (or carburettors on some early variants), and fuel pumps require attention. K-Jetronic systems can develop leaks over time, and the airflow meter unit requires careful handling.
- Cooling System: Overheating can cause significant damage, so maintaining the radiator, hoses, water pump, and thermostat is vital.
- Valve Adjustments: While OHC engines typically have self-adjusting tappets (hydraulic lifters), they can occasionally require inspection or adjustment, especially if valve train noise is present.
Common issues can include vacuum leaks, worn fuel injectors, failing fuel pump relays (especially on K-Jetronic systems), and the typical wear and tear associated with age, such as deteriorating rubber hoses and seals.
Frequently Asked Questions
How many valves does a standard Mercedes M117 engine have?
A standard Mercedes M117 engine features two valves per cylinder. As it is a V8 engine, this means it has a total of 16 valves (2 valves/cylinder x 8 cylinders).
What is the difference between M117 and M116 engines?
The M116 is also a Mercedes-Benz V8 engine, but it is generally a smaller displacement engine, typically 3.5L or 3.8L, whereas the M117 spans from 4.5L up to 5.6L. Both share a similar V8 architecture and OHC design, but the M117 is the larger, more powerful variant.
Are M117 engines reliable?
Yes, M117 engines are renowned for their reliability and durability when properly maintained. Their robust construction allows them to withstand high mileage and demanding use.
What cars used the M117 engine?
The M117 engine was used in a wide range of Mercedes-Benz models, including the W107 (350SL, 450SL, 500SL), C107 (450SLC, 500SLC), W116 (450SE, 450SEL), W126 (380SE/SEL/SEC, 500SE/SEL/SEC, 560SE/SEL/SEC), and C126 (380SEC, 500SEC, 560SEC). It also powered some earlier models like the W108 and W109.
Conclusion
The Mercedes-Benz M117 V8 engine is a testament to German engineering, offering a blend of performance, refinement, and longevity. Whether in its standard 16-valve form or the rare and powerful 32-valve AMG variants, the M117 remains a desirable and engaging powerplant for classic Mercedes-Benz enthusiasts. Understanding its various displacements, technical nuances, and maintenance requirements is key to appreciating and preserving these automotive icons.
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