Mercedes-AMG has taken the wraps off the new M139 version of its transverse 2.0-liter turbocharged 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.