Mercedes-AMG has taken the wraps off the new M139 version of its transverse 2.0-liter turbocharged four-cylinder, and the maximum horsepower figure is a mind-bender. It’s 416, or 40 more than stumped up by the M133 engine it replaces. That means the M139 supplants the M133 as the world’s most powerful series-produced four-banger. The 416-hp, 369-lb-ft version is destined for certain S-badged AMG models; non-S versions will get a slightly detuned version rated at 382 horsepower and 354 lb-ft.
As notable as the power output is the way it’s delivered. While the old M133 had the squared-off torque curve typical of a turbo four, the M139 is designed to deliver the free-revving feel of a naturally aspirated engine. The torque still builds quickly at low rpm, but the rise is more gradual and the torque peak (which is up 19 lb-ft from last year) is set way up high at 5,000 to 5,250 RPM, with peak horsepower coming online at 6,750 rpm. Redline is 7,200 rpm. (The non-S engine’s torque peaks slightly lower, between 4,750 and 5,000 rpm.)
In order to achieve these new numbers, AMG started with a high-strength, chill-cast, closed-deck aluminum block strong enough to withstand diesel-like peak combustion pressures in excess of 2,300 psi. AMG’s patented “nanoslide” coating on the piston liners reduces friction, as does a change to 0W20-grade oil.
The cylinder head is an all-new design, with plugs and injectors rotated 90 degrees compared to the M133 to allow for larger exhaust valves. A new two-stage fuel-injection system combines direct injectors that spray into the combustion chamber with secondary injectors located in the intake manifold.
The twin-scroll turbocharger now employs roller bearings to reduce friction and an electronic wastegate actuator for more precise control. The turbine housing is divided into two separate flow passages, each fed by a pair of cylinders. The dual passages serve a similar function to equal-length exhaust headers, ensuring that the exhaust pulses of the cylinders do not interfere with one another. The turbo is cooled by water, oil, and air, the later directed from the grille by ducting and a specially shaped engine cover. Peak boost is just under 30.5 psi for the S engine and just over 27.5 for the base engine.
With such a high specific power output, cooling was a major concern. To that end, the M139 employs a high-flow electric water pump, which also allows quicker warm up and better water circulation at low engine speeds. A secondary radiator lives in the front fender well. In order to keep all components at optimum temperatures, the block and head have separate cooling circuits so that the head can be maintained at a lower temperature than the block. On S engines, the air-conditioning system helps to reduce the intercooler’s temperature under maximum-power conditions.
If all that weren’t enough, the engine has been flipped 180 degrees as compared to its predecessor so that the intake manifold is up front and the turbocharger and exhaust manifold are at the rear. This simplifies the intake plumbing and eliminates the need to run the exhaust pipe under the engine. It also lowers the engine’s height, which will allow for lower hoodlines on future vehicles.
Like other AMG engines, the M139 is hand-built by a single specially trained technician as part of AMG’s “One Man, One Engine” philosophy (the name persists despite the fact that AMG employs female engine assemblers). For the M139, AMG has initiated a new production process in which each technician builds his or her engine on an advanced assembly trolley, which is rolled from station to station. The trolley monitors the assembly process, ensuring that the technician uses parts and tools in the proper order. Tools that formerly hung from the ceiling have been replaced by a cordless fastener with an “indoor GPS” system. The tool’s electronics can sense the fastener’s exact position on the engine and set the torque accordingly. Instead of walking to the parts rack every few minutes, each technician is followed by a robotized parts car that contains all the components for a single engine.
Mercedes has not made any official announcement as to which vehicles the M139 will power, but one doesn’t need a crystal ball: The M133 currently powers all 45-series AMG cars, and the M139 will undoubtedly follow suit in vehicles like the next-gen A45 and CLA45.