The Mercedes-Benz M278 is a family of direct injected, Bi-turbocharged, V8 gasoline automotive piston engines. The M278 is derived from the company's previous M273 V8 engine, sharing its bore pitch, aluminium engine block, and Silitec aluminium/silicon low-friction cylinder liners. In contrast to the port-injected M273, the M278 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. 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. While the M273 was naturally aspirated, the M278 features twin turbochargers from Honeywell, one per cylinder bank, producing 0.9 bar boost pressure in most configurations. Mercedes-Benz estimated that these changes, with vehicle modifications such as a stop-start system, give the 4.7–litre M278 22% lower fuel consumption and CO2 emissions than the 5.5–litre M273 while producing more power 320 kW versus 285 kW and torque 700 Nm versus 530 Nm. The entire M278 lineup avoids the United States Gas Guzzler Tax, a first for V8 production engines from Mercedes-Benz.

M278

The basic M278 has a displacement of 4663 cc with a bore and stroke of 92.9x86 mm. Output is 320 kW at 5,250 rpm with 700 Nm of torque at 1,800-3,500 rpm for S-Class, CL-Class, SL-Class, and GL-Class models. CLS-Class, E-Class, and M-Class models are detuned to 300 kW with 600 Nm of torque at 1,600 rpm. Although it no longer corresponds with the engine displacement, all of the above models are still badged as "550". The GL-Class, besides the GL550 above, also features the GL450 trim that carries a detuned version of the 4.7 L engine making 270 kW and 550 Nm For 2014 S-Class models (chassis code W222), power is increased to 335 kW at 5,250 rpm, while torque remains at 700 Nm between 1,800-3,500 rpm. . These engines are mated to the 7G-Tronic 7-speed automatic transmission, and the new 9G-Tronic 9-speed automatic transmission. Applications:

M157 AMG

The second variant, designated M157, is tuned by Mercedes-AMG for use in higher-performance models. This version has a displacement of 5461 cc with a bore and stroke of 98x90.5 mm. Increased power and torque comes from the increased displacement as well as higher boost pressure of 1 bar. There are six states of output with the M157. For the S-Class and CL-Class, power is 400 kW at 5,500 rpm with 800 Nm of torque at 2,000-4,500 rpm, or 420 kW at 5,500 rpm with 900 Nm of torque at 2,500-3,750 rpm with the optional AMG Performance Package. For the 2013-15 SL-Class, power is 395 kW or 415 kW with the optional AMG Performance Package. For the 2012-2013 E-Class and CLS-Class, power is 386 kW with 700 Nm of torque in standard tune, or 410 kW with 800 Nm of torque with the AMG Performance Package. Beginning with the 2014 E-Class and CLS-Class, power increases to 410 kW 720 Nm of torque for standard tune, or 430 kW with 800 Nm of torque for "S-Model" variants. At the same time for SL-Class, power increases to 430 kW and 900 Nm. These engines are mated to the AMG Speedshift MCT 7-speed semi-automatic transmission, which replaces the 7G-Tronic's torque converter with a wet clutch pack. Note that this MCT 7-speed can handle considerably more torque and is not the same unit as the dual-clutch transmission found on the Mercedes-Benz SLS AMG. Applications: The M157 engine will replace the previous M156 in most of the AMG lineup. Despite the 5.5–litre displacement, all models are designated "63" for marketing purposes.

M152

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 cylinder deactivation variable displacement system for improved fuel economy (up to 30 percent better than the M113 E55 engine used in the previous model). Output is 310 kW at 6,800 rpm, with 540 Nm of torque at 4,500 rpm. Applications