There used to be a time when a four-cylinder turbocharged engine with more than 250 horsepower was a rarity, but now the new M139 engine from Mercedes-AMG is here and it packs 415 horsepower and 369 pound-feet of torque. It will power a range of Mercedes-AMG vehicles including the A45 and CLA45 sedans and the GLA45 SUV.
The M139 is a 2.0-liter transverse-mounted turbocharged inline-four that will supplant the aging M133 engine currently found in the A45, CLA45 and GLA45. It is available in both a standard and S-badged form. In the base version, it makes 382 horsepower and 354 lb-ft of torque; in the more powerful S-model, it produces 416 horses and 369 pound-feet.
According to the company, it has achieved these power gains through a number of tweaks that increase power and response. These include a new ‘torque filling’ set of measures that allow a greater range of boost pressure control and direct and manifold injection, as well as a larger single twin-scroll turbo with a roller bearing compressor and turbine wheels.
Another major change comes from a 180-degree reorientation of the engine that sees the exhaust manifold and turbo relocated to the back of the engine against the firewall. This moves the engine’s plumbing further back and away from the cylinder head, which allows for more efficient cooling.
A forged steel crankshaft, forged aluminum pistons and Nanoslide cylinder coating are also a part of the M139’s design. These changes make the M139 less prone to friction in its cylinder linings, which is a huge benefit to the M139’s ability to deliver maximum torque at low and high speeds.
Other changes include an all-new intake system that features a larger and narrower plenum, as well as improved airflow and air quality. Additionally, it uses a new four-bar air sensor that enables greater power gains over the OEM unit and reduces the need for an electronic throttle position sensor.
Finally, the M139 has a high-flow electric water pump that helps to maintain optimum temperatures for each of the individual components. Those components include the block, heads, and turbochargers. A secondary radiator located in the front fender well also aids in cooling.
The M139 also features an intercooler that uses a new water pump and a special cooling circuit. This design reduces the temperature of the intercooler under maximum-power conditions and ensures that it is always cool enough to operate without any problems.
Despite its obscene amount of power, the M139 is also compact and highly efficient. Its cylinder bore diameter is smaller than those of the older M133, and the crankshaft is lighter thanks to the M139’s new design.
Assembling the M139 is a complex process that is performed by one specially trained technician using an advanced assembly trolley that moves from station to station. It monitors each stage of the build, ensuring that the technician uses the parts and tools in the proper order.
Assembling the M139 isn’t as simple as it sounds, and the team at Affalterbach had to rethink their entire build process in order to get it right. For this reason, AMG will continue its “One Man, One Engine” production philosophy where each technician will assemble their engine by hand, rather than use machines to do it. AMG’s “indoor GPS” system will be able to pinpoint the location of each fastener and set torque accordingly.