Mercedes-Benz M278 engine

Mercedes-Benz M278
Manufacturer Daimler AG
Production 2010–
Predecessor Mercedes-Benz M273, Mercedes-Benz M156

The Mercedes-Benz M278[1] engine is a family of direct injected, V8 gasoline automotive piston engines.

The M278 is derived from the company's previous M273 V8 engine, sharing its bore pitch, aluminum engine block, and Silitec aluminum/silicon low-friction cylinder liners.[2] In contrast to the naturally aspirated M273, however, the M278 features twin turbochargers, one per cylinder bank, producing up to 0.9 bar boost pressure.[2] The M278 also features gasoline direct injection, with piezo-electrically actuated fuel injectors for more precise fuel delivery, and multi-spark ignition, which enables the spark plugs to be fired multiple times over the combustion sequence for more efficient combustion.[2] Other changes relative to the M273 include an increased adjustment range for the variable valve timing system, a new timing chain arrangement, and new engine accessories (such as the oil pump, water pump, fuel pump, and alternator) which reduce parasitic loads. Many of these new features are shared with the M276 V6 engine family, which was announced at the same time.[2]

Mercedes-Benz estimate that these changes, in conjunction with vehicle modifications such as a stop-start system, allow the 4.7 liter M278 to have 22% lower fuel consumption and CO2 emissions than the 5.5 liter M273 while producing more power (429 hp versus 382 hp) and torque (516 ft·lbf versus 391 ft·lbf).[2]

The entire M278 lineup avoids the United States Gas Guzzler Tax, a first for V8 production engines from Mercedes-Benz.[3]



Three versions of the M278 engine are in production or have been announced.

M278 (base)

The basic M278 has a displacement of 4.7 liters (4663 cc) with a bore of 92.9 mm and stroke of 86 mm. Output is 429 hp (320 kW, 435 PS) at 5250 rpm with 516 ft·lbf (700 N·m) of torque at 1800-3500 rpm for S-Class and CL-Class models,[2] while CLS-Class models are derated to 402 hp (300 kW) with 443 ft·lbf (600 N·m) of torque at 1600 rpm.[4]



The second variant, designated M157[5], is tuned by Mercedes-AMG for use in higher-performance models. This version has a displacement of 5.5 liters (5461 cc) with a bore of 98.0 mm and stroke of 90.5 mm.[6] Increased power and torque comes from the increased displacement as well as higher boost pressure of 1.0 bar. Output is 536 hp (400 kW, 544 PS) at 5500 rpm with 590 ft·lbf (800 N·m) of torque at 2000-4500 rpm, or 563 hp (420 kW, 571 PS) at 5500 rpm with 664 ft·lbf (900 N·m) of torque at 2500-3750 rpm with the optional AMG Performance Package.[6] The M157 engine in high-performance E-Class and CLS-Class models will produce 525 hp (386 kW) and 516 ft·lbf (700 N·m) of torque, or 557 hp (410 kW) and 590 ft·lbf (800 N·m) of torque with the AMG Performance Package. [7] These engines are mated to the AMG Speedshift MCT 7-speed dual-clutch transmission.[8]


The M157 engine will replace the previous M156 in most of the AMG lineup. Despite the 5.5 liter displacement, all models are designated "63" for marketing purposes.[10]


The third variant, designated M152, is a naturally aspirated derivative of the M157 engine, sharing the same displacement, direct injection, and many other features. The M152 engine includes a variable displacement system for improved fuel economy (up to 30 percent better than the M113 E55 engine used in the previous model). Output is 415 hp at 6800 rpm, with 390 ft·lbf of torque at 4500 rpm. [11]



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