Mercedes-Benz M278 Specifications
| Engine Model: Mercedes-Benz M278 |
| Engine Type: 4-cycle 8-cylinder DOHC 32-valve twin-turbocharged liquid-cooled gasoline |
| Total Displacement: 284.5 cu.in (4.66 L) |
| Rated Engine Power: 435-585 Hp (324-436 kW) at 5500 rpm |
| Fuel System Type: Direct fuel injection |
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The Mercedes-Benz M278 engine is a
direct-injected, twin-turbocharged V8 gasoline powerplant that served as
the brand's flagship eight-cylinder engine from 2010 until the early
2020s. It succeeded the naturally aspirated M273 and supercharged M113K
engines, representing a decisive shift towards forced induction for
efficiency and performance. This engine employs a "hot-V" configuration,
where the two turbochargers are mounted inside the cylinder bank
V-angle, close to the exhaust manifolds.
This innovative packaging reduces turbo lag, lowers exhaust emissions,
and improves packaging within the engine bay. The M278 combines a
lightweight aluminum block with advanced technologies such as
piezoelectric direct fuel injection, air-to-water intercooling, and
variable valve timing. It is renowned for delivering substantial low-end
torque, immediate throttle response, and impressive specific output
while meeting stringent global emissions standards.
Engine family: Mercedes-Benz M278.
Engine type: 90-degree V8, four-stroke Otto cycle, twin-turbocharged
with "hot-V" layout.
Displacement: 4663 cc (284.5 cubic inches).
Bore: 92.9 mm (3.657 inches).
Stroke: 86.0 mm (3.386 inches).
Compression ratio: 10.5:1.
Maximum power output: Ranges from 435 Hp (324 kW) at 5250-5500 rpm to
585 Hp (436 kW) at 5500 rpm in AMG S-Model applications (M278 DE 46 AL).
Maximum torque output: Ranges from 516 lb-ft (700 Nm) at 1800-3500 rpm
to 664 lb-ft (900 Nm) at 2250-3750 rpm in high-output versions.
Redline: 6000-6500 rpm.
Firing order: 1-5-4-8-6-3-7-2.
Engine orientation: Longitudinal.
Aspiration: Twin turbochargers with air-to-water intercoolers.
Fuel type: Premium unleaded gasoline (91 RON minimum, 95 RON
recommended).
Recommended oil grade: SAE 0W-40, meeting Mercedes-Benz specification
229.5.
Oil capacity: 8.5 liters (9.0 U.S. quarts), including filter.
Coolant capacity: 14.5 liters (15.3 U.S. quarts) for main circuit.
The cylinder block is a high-pressure die-cast aluminum alloy
(AlSi17Cu4Mg) with patented SILITEC cylinder surfaces. This technology
uses a rotocasting process to create a hypereutectic silicon-aluminum
surface within the bore, eliminating the need for separate iron liners
and improving heat transfer. The block is a closed-deck design for
maximum rigidity under high boost pressures.
The crankshaft is a forged steel unit supported by five main bearings.
Main bearing caps are made from nodular cast iron and are secured with
four bolts each: two vertical bolts and two lateral cross-bolts.
Connecting rods are forged from micro-alloyed steel. Pistons are cast
aluminum alloy with cooling galleries, fed by dedicated oil spray jets.
Each piston uses two low-friction steel compression rings and one oil
control ring.
Each cylinder bank utilizes a separate cast aluminum alloy cylinder head
with four valves per cylinder (two intake, two exhaust). The valvetrain
employs dual overhead camshafts (DOHC) per bank, driven by a dual-stage
chain system from the crankshaft. Camshaft adjustment is continuous on
both the intake and exhaust camshafts via electro-hydraulic adjusters
(CONTI), allowing a wide range of valve timing control.
Valve actuation is via roller-finger followers with hydraulic lash
adjusters, ensuring zero-maintenance operation. Intake valves are 35.0
mm (1.378 inches) in diameter, while exhaust valves are 29.0 mm (1.142
inches). The cylinder heads feature crossflow design with centrally
located direct fuel injectors and spark plugs.
The fuel system is a stratified direct injection setup using Bosch
piezoelectric injectors. These injectors operate at very high pressure -
up to 200 bar (2900 psi) - and allow for multiple, precise injection
events per cycle for optimal mixture preparation and combustion.
Fuel is supplied by two high-pressure fuel pumps, driven by a three-lobe
cam on the left intake camshaft. A low-pressure electric pump in the
fuel tank feeds the high-pressure pumps. The engine control unit (Bosch
ME 9.7 or MED 17) manages injection timing, duration, and pressure. This
direct injection system reduces fuel consumption, lowers exhaust
temperatures, and enables higher compression ratios despite forced
induction.
The lubrication system is a pressure-fed, variable-displacement wet-sump
design. A vane-type oil pump with electronically controlled displacement
adjusts oil pressure based on engine demand, reducing parasitic losses.
The oil pan is a cast aluminum design with integrated baffles.
Oil is drawn through a pickup screen, pressurized, and routed through a
full-flow cartridge-style oil filter located atop the engine. From the
filter housing, oil feeds the main gallery, supplying the crankshaft
bearings, camshaft bearings, timing chain tensioners, and turbocharger
cartridges. The system includes a dedicated oil cooler integrated into
the cooling circuit. Oil level is monitored by an electronic sensor.
The cooling system employs three separate circuits: a high-temperature
circuit for the engine block and heads, a low-temperature circuit for
the charge air coolers, and a dedicated circuit for the turbocharger
bearing housings and the air-conditioning condenser. This separation
optimizes thermal management. Electric coolant pumps operate
independently of engine speed for the intercooler and turbocharger
circuits.
The twin turbochargers are mono-scroll units mounted within the V-angle.
They are fed by individual exhaust manifolds and feature integrated
wastegates. Charge air is cooled by compact air-to-water intercoolers
mounted directly at the intake ports. The ignition system is a
coil-on-plug design with iridium spark plugs. An engine stop-start
system (ECO) is standard.
The "hot-V" configuration results in compact external dimensions
relative to its output. Approximate length is 700 mm (27.56 inches).
Approximate width is 800 mm (31.50 inches). Approximate height is 700 mm
(27.56 inches). These dimensions contribute to favorable packaging in
various chassis. The dry weight of a complete M278 engine, including all
fluids and standard accessories, is approximately 205 kg (452 lbs). The
extensive use of aluminum alloys contributes to this favorable
power-to-weight ratio.
Engine oil and filter change intervals are governed by the Flexible
Service System (FSS), with extended intervals up to 20,000 km (12,427
miles) or 1 year under favorable conditions. Severe service warrants
more frequent changes. Spark plug replacement is required every 60,000
km (37,282 miles) or 4 years.
The accessory drive belt should be inspected every 60,000 km and
replaced at signs of wear. Although designed for longevity, the timing
chain and guides require inspection for wear or stretching after 150,000
km (93,206 miles). Coolant for all three circuits must be replaced every
250,000 km (155,343 miles) or 15 years. The high-pressure fuel filter is
a scheduled maintenance item.
All torque values are for clean threads lightly coated with engine oil
unless specified. Cylinder head bolts are tightened in a multi-stage
angular torque procedure: initial torque 50 Nm (37 lb-ft), then an
additional 90-degree turn, followed by a final 90-degree turn. Main
bearing cap bolts (vertical): 50 Nm (37 lb-ft) plus 90 degrees.
Main bearing cap cross-bolts: 50 Nm (37 lb-ft). Connecting rod cap
bolts: 30 Nm (22 lb-ft) plus 90 degrees. Crankshaft pulley bolt: 200 Nm
(148 lb-ft) plus an additional 90-degree angle. Camshaft sprocket bolts:
100 Nm (74 lb-ft). Spark plugs: 23 Nm (17 lb-ft). Oil drain plug: 40 Nm
(30 lb-ft).
The Mercedes-Benz M278 engine was deployed across the brand's luxury and
performance lineup from approximately 2010 to 2020. Primary applications
include: W221 and W222 chassis (S-Class: S 500, S 550). C217 and A217
chassis (S-Class Coupe and Convertible: S 550). W218 chassis (CLS-Class:
CLS 550). X166 chassis (GL-Class/GL 450, GLS 450).
C292 chassis (SL-Class: SL 550). High-performance AMG applications
include the Mercedes-AMG GT 4-Door Coupe (as the M178 variant shares
core architecture) and the Mercedes-Maybach S 580. It also saw service
in the Mercedes-Benz G550 (W463). The engine was gradually replaced by
the in-line six-cylinder M256 and the newer V8 M176.
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