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Mercedes-Benz claims its AMG-designed M 139 is the world’s most-powerful 4-cylinder engine. (Mercedes-Benz)

Mercedes-AMG extracts world-record power from new four-cylinder engine

Mercedes-Benz engineers delight in setting new technology records—because they can then start a new program to break them. At Mercedes-AMG—the out-and-out performance side of the business—that urge often brings some remarkable results, the latest being a massive power output from its new 2.0-L 4-cyl. AMG’s “fundamentally new” M 139 is bluntly claimed to be the world’s most powerful turbocharged 4-cyl. in series production. 

The raw figures for the M 139S version are an output from 310 kW (421 hp) from 1991 cc of displacement; the figure is up 30 kW (41 hp) over its forebear 4-pot muscle-machinery, the M 133. Peak output is at 6750 rpm and maximum engine speed is 7200 rpm; AMG’s 4-cyl. powerhouse also generates 500 Nm (369 lb-ft) at 5000 to 5250 rpm.

Tech extravaganza
To help achieve the M 139’s outsized performance figures is a sparkling constellation of technologies that span crankcase strength, turbocharger subtlety and fuel injection capability, plus exceptional systems cooperation. With the propulsion conversation increasingly dominated by electric vehicles (EVs) and hybrid-electric vehicles (HEVs) came this comment from Mercedes-AMG Chairman, Tobias Moers: “Not only is the output per liter unrivalled for a turbocharged engine, the high level of efficiency also demonstrates that the internal combustion engine still has further potential.” 

Interestingly, the M 139—like other Mercedes-AMG engines, assembled on a “one man, one engine” basis—comes in two versions: the S and what Mercedes-AMG terms “the basic version” with an output of 285 kW (387hp) that isn’t exactly a wimp either. The decision to offer a lower-power option was to meet customer wishes and has proved successful in the V8-engine AMG models, stated the company. Both versions are said to have a specifically-calibrated torque curve—dubbed “torque shaping”—similar to that of a naturally-aspirated engine. EV engineers still might not be impressed. 

Substantial construction
Squeezing so much power from a 2.0-L engine emphasizes the need for structural strength. The M 139 has a “chill-cast” aluminum crankcase to help achieve it. Molten aluminum is poured into a metallic, water-cooled mold to speed cooling and solidification of the melt, leading to a fine-grained, dense structure for very high strength, stated the company.

Closed-deck construction, a technique borrowed from racing, delivers low weight and “impressive rigidity” to cope with cylinder pressures of up to 160 bar (2321 psi). The transverse-engine layout positions the turbocharger and exhaust manifold at the rear, the intake at the front. This is to facilitate a hood line and general frontal area that improves aerodynamic efficiency. Intake-air ducting also is said to be improved. 

Roller-bearing turbo  
The M139’s new twin-scroll turbocharger housing has two flow passages positioned in parallel. Friction-reducing roller bearings are used for compressor and turbine shafts. Maximum charge pressure is 2.1 bar (30.5 psi) for the M 139S. An electronically-managed wastegate gives improved charge-pressure control to help part-load responsiveness; the wastegate control unit (WCU) receives information regarding charge pressure, throttle flap position and the potential for knock, with “modifying” signals listed as intake pressure, engine temperature, engine speed and atmospheric pressure, together allowing a brief overboost function for pedal-to-the-metal moments. 

Meanwhile, the milder M 139 gets an exhaust-valve makeover. Mercedes-AMG explained that repositioning and slightly angling the engine’s fuel-injection nozzles and sparkplugs in the cylinder head facilitates “greatly enlarging” the exhaust valves compared to the M 133, reducing overall piston venting. Thermal aspects of the new engine are significant, with more efficient cylinder-head cooling required and met via seating rings with reduced installed height and a cooling bore hole close to the combustion chamber in the web area between the exhaust-valve seating rings.

Mercedes’ Camtronic variable-valve control is used on the exhaust side and a multi-layer corrugated-metal seal is used to isolate the cylinder head from crankcase. Thermal optimization also involves a smart cooling system, with an extra radiator in the wheel arch as a supplement to the regular radiator and a low temperature circuit for air/water cooling. Transmission-oil cooling is part of the engine’s coolant circuit and there is a heat exchanger positioned on the transmission. An on-demand electric water pump operates independently of the engine. 

The M 139 uses 2-stage fuel injection. The first has very quick and precise piezo injectors operating at pressures up to 200 bar (2900 psi) for in-cylinder direct-injection. The second stage comprises intake-manifold (port) injection using solenoid valves. Fuel-supply operating pressure is 6.7 bar (97 psi). The first vehicle to use the M139 reportedly will be the A45 hatchback launched later in 2019, while likely U.S. models could include the CLA sedan and GLA and GLB crossovers.

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