Mercedes-Benz M120 Specifications
| Engine Model: Mercedes-Benz M120 |
| Engine Type: 4-cycle 12-cylinder DOHC 48-valve liquid-cooled gasoline |
| Total Displacement: 365.3 cu.in (5.98 L) |
| Rated Engine Power: 390-525 Hp (290-391 kW) at 5200 rpm |
| Fuel System Type: Electronic fuel injection |
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The Mercedes-Benz M120 is a naturally aspirated
60-degree V12 gasoline engine that served as the technological pinnacle of the
Mercedes-Benz passenger car lineup from its introduction in 1991 through its
final production applications in 2001. Conceived as a direct response to the BMW
M70 V12, the M120 was engineered from the outset as a statement of superlative
capability, utilizing advanced materials and manufacturing techniques to achieve
a combination of seamless refinement, immense power output, and structural
integrity that was unprecedented for a series-production 12-cylinder engine of
its era.
The engine’s fundamental architecture was so robust that it transcended its
original role, evolving beyond the luxury S-Class and SL-Class grand tourers to
become the sole power source for the Pagani Zonda hypercar and the basis for the
race-derived CLK GTR, securing its legacy as one of the most significant
internal combustion engines of the late 20th century.
The M120 represented a paradigm shift for Mercedes-Benz, moving away from the
single-overhead-cam (SOHC) V8s and the V12 that preceded it in the W100 600
"Grosser" to a modern, high-output, dual-overhead-camshaft (DOHC) design. Its
defining characteristic is over-engineering; the aluminum block features
closed-deck construction and is impregnated with a high-silicon content to
create a durable, low-friction bore surface without the need for cast-iron
cylinder liners.
The four-valve-per-cylinder cylinder heads, with their variable valve timing on
the intake side, allowed for a flat torque curve and a broad powerband that made
the engine feel effortless at any speed. While early iterations utilized the
Bosch LH-Jetronic fuel injection system, later versions transitioned to the more
sophisticated Motronic engine management, improving drivability and diagnostic
capabilities.
The engine’s reputation for mechanical longevity is well-earned, with the core
rotating assembly being capable of withstanding significant power increases
beyond its original 6.0-liter displacement, a fact proven by the 7.3-liter
versions developed for the Pagani Zonda and the 7.1-liter AMG models. However,
its complexity introduces significant maintenance demands in its later years,
primarily due to the degradation of biodegradable wiring harnesses and the
complexity of its dual-electronic throttle body system. When maintained, the
M120 delivers an experience defined by a near-silent idle, instantaneous
throttle response, and a linear surge of torque that is more akin to a
high-performance turbine than a reciprocating engine.
Production Period: 1991-2001.
Engine Code: M120 (E60, E67, E70, E73 variants).
Configuration: 60° V12.
Displacement: 5,987 cc (365.3 cu.in) for the standard 6.0L.
Bore: 89.0 mm (3.50 in).
Stroke: 80.2 mm (3.16 in).
Compression Ratio: 10.0:1 (standard 6.0L).
Firing Order: 1-12-4-9-2-11-6-7-5-10-3-8.
Maximum Engine Speed: 6,200 rpm (electronically limited).
Engine Management: Bosch LH-Jetronic with KE-Jetronic backup (1991-1995); Bosch
ME 1.0 Motronic (1995-2001).
Power Output (SAE Net)
1991-1992 M120 E60: 402 hp (300 kW) @ 5,200 rpm; 428 lb-ft (580 Nm) @ 3,800 rpm
1993-1999 M120 E60: 389-394 hp (290 kW) @ 5,200 rpm; 420 lb-ft (570 Nm) @ 3,800
rpm.
M120 E70 (7.1L AMG): 496-510 hp (370-380 kW); 553 lb-ft (750 Nm).
M120 E73 (7.3L Pagani): 525 hp (391 kW).
The M120 cylinder block is a closed-deck casting
manufactured from a high-strength aluminum-silicon alloy (Alusil). This material
choice was critical to the engine’s design philosophy, eliminating the need for
heavy pressed-in cast-iron cylinder liners. The cylinder bores are machined and
then chemically etched to expose the hard silicon particles, creating a bore
surface of exceptional hardness and low friction against the aluminum pistons.
The block’s closed-deck design, where the water jacket does not surround the top
of the cylinders, provides maximum rigidity to the cylinder bores under high
combustion pressures and is a primary factor in the engine’s ability to be
reliably enlarged to displacements beyond 7.0 liters.
The crankcase features a deep-skirt design that extends below the crankshaft
centerline, providing a rigid support structure for the main bearing caps, which
are made of high-strength sintered steel and secured with cross-bolts to the
side of the block. This construction results in a very stiff assembly that
minimizes vibration and ensures consistent bearing alignment under load. The
block incorporates a single-piece cast aluminum oil pan that also contributes to
the overall structural rigidity of the engine assembly.
The cylinder heads are also constructed from an
aluminum-silicon alloy and utilize a dual-overhead-camshaft (DOHC) configuration
with four valves per cylinder, totaling 48 valves. Each head is driven by its
own timing chain from the crankshaft. The intake valves are actuated by a
hydraulically controlled camshaft adjuster system on the intake camshafts,
providing continuously variable valve timing of up to 30 degrees of crank angle.
This system optimizes volumetric efficiency across the entire rev range,
contributing to the engine’s broad, flat torque curve.
The valve diameters are substantial for the bore size, with intake valves
measuring 35.0 mm (1.38 in) and exhaust valves measuring 31.0 mm (1.22 in). The
valve seats are sintered metal inserts for durability, and the valve guides are
made from a high-strength bronze alloy. The valvetrain uses bucket-type
hydraulic valve lash adjusters, which eliminate the need for routine valve
clearance adjustments. The camshafts themselves are hollow to reduce rotational
mass, contributing to the engine’s rapid throttle response.
The fuel system for the M120 underwent a significant
evolution during its production life. From 1991 until mid-1995, the engine was
equipped with a dual-path Bosch LH-Jetronic electronic fuel injection system.
This system utilized a hot-wire air mass meter for each bank of six cylinders,
operating two independent fuel rails and fuel distributors.
A backup KE-Jetronic mechanical fuel injection system was integrated as a
failsafe, ensuring the vehicle could remain operational in the event of a
primary electronic system failure. From late 1995 onward, the system
transitioned to a single Bosch ME 1.0 Motronic engine management system. This
centralized management integrated ignition and fuel injection control, utilizing
a single mass air flow sensor and sequential fuel injection.
The later Motronic system improved cold-start behavior, reduced emissions, and
provided more precise fuel metering across the engine’s operating range. All
variants utilize high-pressure electric fuel pumps located within the fuel tank.
The injectors are positioned to direct the fuel spray directly onto the back of
the intake valves, aiding in mixture preparation and valve cooling.
The lubrication system is a dry-sump design, which is
unusual for a series-production passenger car engine but essential for the
M120’s operational profile. A dual-stage oil pump is mounted to the front of the
crankshaft. One stage scavenges oil from the sump, while the other supplies oil
under pressure to the engine. The system utilizes a large, remote oil reservoir
located in the engine bay, which decouples the oil supply from the dynamic
effects of high lateral acceleration.
This ensures uninterrupted oil pressure even during sustained high-speed
cornering, a feature that later proved invaluable in the Pagani Zonda and CLK
GTR applications. The oil cooler is a water-to-oil type, integrated into the
main radiator assembly, which helps bring the engine oil up to operating
temperature quickly and maintains a stable temperature under load. Total system
capacity is approximately 12.0 liters (12.7 qt) including the reservoir. The oil
filter is a full-flow spin-on type with an integrated bypass valve.
The cooling system is designed to manage the
significant thermal load generated by the V12’s 48 valves and 12 cylinders. The
system uses a high-capacity, dual-row crossflow radiator constructed from
aluminum with plastic end tanks. Two independent electric cooling fans provide
airflow, operating at two speeds based on signals from the engine control unit
and the radiator outlet temperature sensor. The water pump is driven by the
serpentine accessory belt and features a cast aluminum housing bolted directly
to the front of the engine block.
The system incorporates a sophisticated bypass circuit to ensure rapid engine
warm-up and stable thermostat operation. The thermostat is a dual-stage,
wax-element type that begins to open at 85°C (185°F). Coolant flow is directed
to each cylinder bank individually through a dedicated distribution channel cast
into the block, ensuring uniform cooling across all 12 cylinders. The coolant
capacity of the system, including the heater core and expansion tank, is 16.0
liters (16.9 qt).
| Intake and Exhaust Systems |
Intake System: The intake manifold is a complex,
two-piece cast aluminum assembly featuring a resonance induction system with
variable-length intake runners. A set of dual throttle bodies, electronically
actuated (known as the ETA system), controls airflow. The intake plenum is
designed to balance the pressure pulses between the two cylinder banks, creating
a seamless power delivery. The air filter housing is a large, dual-element unit
designed to ensure minimal flow restriction.
Exhaust System: The engine is equipped with two complete, independent exhaust
systems, one for each bank of six cylinders. Each system incorporates its own
cast iron exhaust manifold, a pre-catalyst, a main underfloor catalytic
converter, and a separate muffler. The two systems converge only at the final
tailpipe outlets. The use of four oxygen sensors (two per bank) allows the
engine control unit to monitor and adjust the air-fuel ratio for each cylinder
bank independently, maintaining precise emissions control.
| Ignition and Electrical System |
Ignition System: The M120 utilizes a distributorless
ignition system. Two separate ignition control modules manage six direct-fire
ignition coils each, with each coil serving a single spark plug. This
configuration eliminates high-tension spark plug wires and the associated
losses, providing a very high-energy spark that is maintained with precision
across the engine’s speed range. The system receives its trigger signal from a
60-2 tooth crankshaft position sensor mounted at the front of the engine.
Electrical System: The engine management relies on a network of sensors and
actuators, including camshaft position sensors, knock sensors for each cylinder
bank, coolant temperature sensors, and intake air temperature sensors. The
wiring harness is constructed with specialized insulation that was designed to
be environmentally friendly. This material, used on pre-1996 models, is
susceptible to becoming brittle and disintegrating over time, leading to
electrical faults that are a well-known service consideration for early M120
engines.
Overall Length: 805 mm (31.7 in)
Overall Width: 780 mm (30.7 in)
Overall Height: 725 mm (28.5 in)
Dry Weight (complete engine): 289 kg (637 lbs)
Engine Oil: Synthetic 5W-40 or 10W-40 Mercedes-Benz
specification 229.3 or 229.5.
Oil Capacity (with filter change): 12.0 L (12.7 qt).
Oil Change Interval: 8,000 km (5,000 mi) or 1 year under severe service.
Oil Change Interval: 16,000 km (10,000 mi) under normal conditions.
Spark Plug Type: Bosch F8D4 or NGK BKR6E.
Spark Plug Gap: 1.0 mm (0.040 in).
Spark Plug Change Interval: 48,000 km (30,000 mi).
Coolant Capacity: 16.0 L (16.9 qt).
Coolant Specification: Mercedes-Benz approved phosphate-free, silicate-free
antifreeze).
Valve Clearance: Hydraulic lifters; no adjustment required.
Engine Idle Speed: 650-750 rpm.
Ignition Timing: Non-adjustable, controlled by ECU.
Connecting Rod Cap Bolts (M9 x 1): 30 Nm (22 lb-ft) +
90°
Main Bearing Cap Cross-Bolts (M8): 20 Nm (15 lb-ft) + 90°
Main Bearing Cap Vertical Bolts (M10): 50 Nm (37 lb-ft) + 90°
Cylinder Head Bolts (M11, 12-point), Stage 1: 40 Nm (30 lb-ft)
Cylinder Head Bolts (M11, 12-point), Stage 2: 80 Nm (59 lb-ft) +90°
Camshaft Bearing Caps: 10 Nm (7 lb-ft) for M6 bolts
Camshaft Bearing Caps: 20 Nm (15 lb-ft) for M7 bolts
Intake Manifold to Cylinder Head: 10 Nm (7 lb-ft)
Exhaust Manifold to Cylinder Head: 25 Nm (18 lb-ft)
Flywheel/Flexplate to Crankshaft (M12 x 1.25): 110 Nm (81 lb-ft) + 90°
Spark Plugs: 25 Nm (18 lb-ft)
Oil Pan to Block (M6): 9 Nm (7 lb-ft)
Mercedes-Benz Passenger
Car:
W140 S-Class (1991-1998): 600 SE, 600 SEL, S 600 (long-wheelbase).
C140 S-Class Coupe (1992-1999): 600 SEC, S 600 Coupe, CL 600.
R129 SL-Class (1992-2001): 600 SL, SL 600.
Mercedes-Benz AMG and Special Models:
W140/R129 AMG: S 70 AMG, SL 70 AMG (7.1L M120 variants).
W140/R129: S 73 AMG, SL 73 AMG (7.3L M120 variants).
C215 CL-Class (initial prototypes): CL 600 (pre-production M120).
Independent Manufacturers And Homologation
Specials:
Pagani Automobili: Zonda C12 (6.0L), Zonda S (7.0L), Zonda F, Zonda Roadster,
Zonda Cinque, Zonda Tricolore, Zonda HP Barchetta (all utilizing M120-based M297
engines with displacements up to 7.3L).
Mercedes-Benz CLK GTR: Road-legal Street version (6.9L M297 variant producing
612 hp for homologation).
Isdera: Commendatore 112i (6.0L M120).
Mega: Mega Track (6.0L M120).
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