The M139 is a successor of M133, a turbocharged inline-four engine produced by Mercedes-Benz, for the next generation A45 AMG and A45 S AMG. It is also a first four-cylinder engine by AMG to be specified with two outputs, to be assembled by hand using "one man, one engine" philosophy, and to be equipped with combined port and direct fuel injection system. At 310 kW (416 hp), M139 is the world's most powerful four-cylinder engine in serial production with specific output of 208 hp per litre or 104 hp per cylinder.

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