The M156 is the first V8 automobile engine designed autonomously by Mercedes-Benz subsidiary Mercedes-AMG, as previous AMG engines have always been based on original Mercedes engines. The engine was designed to be a naturally aspirated racing unit, and will also be used in a number of high-performance "AMG"-badged Mercedes-Benz models.
The M156 displaces 6,208 cc (6.208 L; 378.8 cu in) and shares very little with other Mercedes-Benz engine families like the M155. The bore spacing, block design, and other features are unique to the AMG engine.
Although this engine displaces 6.208 liters, it is marketed as the "6.3" to commemorate Mercedes' famed 6.3L M100 engine, its first production V8.
The engine uses a 102.2 mm (4.02 in) bore and 94.6 mm (3.72 in) stroke. When introduced in the 2007 CLK63, output was 475 hp (354 kW) at 6800 rpm with 630 N·m (464.7 lb·ft) of torque at 5200 rpm. For the 2007 CLS63 and E63, output was 507 hp (378 kW) at 6800 rpm with 630 N·m (464.7 lb·ft) of torque at 5200 rpm. The 2007 ML63 had 503 hp (375 kW), and the 2008 C63 had 451 hp (336 kW). The final 2015 C63 had 500 hp (373 kW).
The engine, however, has been uprated to produce 518 hp (386 kW) (and 465 lb·ft (630 N·m) of torque) in the late S 63, E 63, SL 63, CLS 63 & CL 63 models[1].
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In 2011, a class action lawsuit was filed in United States District Court in New Jersey against Daimler AG, Mercedes-Benz, Mercedes-AMG for alleged defects in the M156 engine contained in AMG vehicles built in 2007-2011 model years leading to premature wear. The plaintiff claimed the combination of cast nodular iron camshafts and 9310 grade steel valve lifters contributed to the premature wear, but the defendants had known about the defect since 2007.
The lawsuit lasted approximately 14-months. In November, 2012, litigation came to a halt when the New Jersey District Court dismissed the plaintiffs’ first amended complaint for lack of standing. The plaintiffs were given the opportunity to further amend their complaint to show that they had standing to sue, but plaintiffs made no further filings with the Court. On January 7, 2013, the Court signed an order closing the case.