Mercedes-Benz M278 engine

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 (13 psi) 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 (435 PS; 429 bhp) versus 285 kW (387 PS; 382 bhp) and torque 700 N⋅m (516 lb⋅ft) versus 530 N⋅m (391 lb⋅ft).

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

The basic M278 has a displacement of 4,663 cc (4.7 L; 284.6 cu in) with a bore and stroke of 92.9 mm × 86 mm (3.66 in × 3.39 in). Output is 320 kW (429 bhp; 435 PS) at 5,250 rpm with 700 N⋅m (516 lb⋅ft) 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 (402 bhp; 408 PS) with 600 N⋅m (443 lb⋅ft) 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 (362 bhp; 367 PS) and 550 N⋅m (406 lb⋅ft)

For 2014 S-Class models (chassis code W222), power is increased to 335 kW (449 bhp; 455 PS) at 5,250 rpm, while torque remains at 700 N⋅m (516 lb⋅ft) 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.