Mercedes-Benz M139 engine
The M139 is a turbocharged inline-four engine produced by Mercedes-Benz. It is the successor of the M133 engine. It is also the 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 , 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. Design. The M139 engine is based on the current Mercedes -Benz M260 engine, which is an upgraded version of the outgoing M270, sharing the same bore and stroke dimension as well as the block. Unlike the normal M260, the AMG engineers rotated the engine block 180 degrees so that the intake system is in the front of the engine while the turbochargers and exhaust headers are situated between the engine and firewall. The rotation optimises the air flow for higher performance and with shorter distance and fewer diversions. This also leads to the "allows the flattest possible and aerodynamically advantageous front section design." The exhaust valves in M139 engine are  bigger than ones in M133 engines for higher flow. The compression ratio is raised to 9.0:1 for M139 from 8.6:1 for M133. The two-stage fuel injection system, a first in AMG four-cylinder engine, has the piezo injectors delivering the fuel directly into the combustion chambers as first stage and solenoid valves in the manifolds as second stage for increased specific output. Performance. The M139 engine has two specific outputs: and for the base version; and and for the S-model.