Mercedes-Benz M278 engine

The Mercedes-Benz M278^[1] is a family of direct injected, Twin-Turbocharged, 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 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.^[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]

While the M273 was naturally aspirated, the M278 features twin turbochargers, one per cylinder bank, producing 0.9 bar boost pressure in most configurations.^[2]

Mercedes-Benz estimate that these changes, in conjunction with vehicle modifications such as a stop-start system, allow the 4.6 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 M278 is also more refined than its predecessor.^[3]

The entire M278 lineup avoids the United States Gas Guzzler Tax, a first for V8 production engines from Mercedes-Benz.^[4]

M278 (base)

The basic M278 has a displacement of 4,663 cc (284.6 cu in) 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, CL-Class, SL-Class, and GL-Class models.^[2] CLS-Class, E-Class, and M-Class models are derated to 402 hp (300 kW) with 443 ft·lbf (600 N·m) of torque at 1600 rpm.^[5] 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 4.6 L engine making 362 horsepower and 406 pounds-feet of torque ^[6]

For 2014 S-Class models (chassis code W222), power is increased to 455 hp (335 kW) at 5250 rpm, while torque remains at 516 ft·lbf (700 N·m) between 1800-3500 rpm. .^[7]

These engines are mated to the 7G-Tronic 7-speed automatic transmission.

Applications:^[2]

• 2011– Mercedes-Benz S-Class (S500 in Europe)
• 2011– Mercedes-Benz CL-Class (CL500 in Europe)^[8]
• 2011– Mercedes-Benz CLS-Class (CLS500 in Europe)
• 2012– Mercedes-Benz E-Class (E550 in the US)
• 2013– Mercedes-Benz GL-Class (GL550 in the US)

M157

The second variant, designated M157,^[9] 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.^[10] Increased power and torque comes from the increased displacement as well as higher boost pressure of 1.0 bar.

There are six states of output with the M157. For the S-Class and CL-Class, power 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.^[10] For the 2012-2013 E-Class and CLS-Class, power is 525 hp (386 kW) with 516 ft·lbf (700 N·m) of torque in standard tune, or 557 hp (410 kW) with 590 ft·lbf (800 N·m) of torque with the AMG Performance Package.^[11] Beginning with the 2014 E-Class and CLS-Class, power increases to 557 hp (410 kW) with 531 ft·lbf (720 N·m) of torque for standard tune, or 585 hp (430 kW) with 590 ft·lbf (800 N·m) of torque for "S-Model" variants.^[12][13]

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.^[14] 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.^[15]

Applications:^[9]

• 2011– Mercedes-Benz S63 AMG
• 2011– Mercedes-Benz CL63 AMG
• 2012– Mercedes-Benz CLS 63 AMG
• 2012– Mercedes-Benz E63 AMG^[14]

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.^[16]

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^[17] (up to 30 percent better than the M113 E55 engine used in the previous model). Output is 415 hp at 6800 rpm, with 398 ft·lbf of torque at 4500 rpm.^[18]

Applications

• 2012– Mercedes-Benz SLK55 AMG

Production

Honeywell Turbo Technologies produced the turbochargers used in Mercedes Benz 4.6L biturbo V8 engines from the S-Class and CL-Class vehicles.^[19]

References