Home: Motoring > Mercedes-AMG A45 4Matic to receive world’s most powerful four-cylinder engine

Mercedes-AMG A45 4Matic to receive world’s most powerful four-cylinder engine

From:Greg Kable 2019-06-07 07:00:01

Newly developed M139 unit hits new heights of power and torque

Mercedes-AMG will introduce the most powerful four-cylinder engine to ever feature in a series production road car when its second-generation A45 4Matic is unveiled later this year.

The newly developed turbocharged 2.0-litre unit, codenamed M139, is claimed to deliver 310kW in its highest state of tune, providing the most extreme iteration of the German car maker’s new headlining four-wheel drive hatchback with 30KW more than the similarly configured M133 engine used by the first-generation A45 4Matic.

Assembled by hand at AMG’s Affalterbach headquarters on the outskirts of Stuttgart in Germany, the A45 4Matic’s new four-cylinder engine has been developed in an engineering program that aims elevate the latest range of compact models from Mercedes-Benz’s performance car division beyond those from rivals Audi Sport and BMW M.

Along with the A45 4Matic, the new AMG powerplant is also planned to feature in the upcoming second-generation CLA45 4Matic, CLA45 4Matic Shooting Brake and GLA45 4Matic as well as a new A45 4Matic sedan and a performance version of Mercedes-Benz’s soon-to-be-revealed GLB SUV that recently commence testing at the hands of AMG engineers, the GLB45 4Matic.

With respective bore and stroke measurements of 83.0mm and 92mm, the M139 engine boasts the same overall swept volume as the M260 powerplant upon which it is based and already features in AMG’s newly introduced A35 4Matic at 1991cm3. It is also the same volume as the older M133 unit.

Such are the number and significance of the changes brought to the transversely mounted four-cylinder unit, however, that AMG’s chairman Tobias Moers describes it as being all-new.

"We already set the benchmark in the segment with the preceding engine. This fundamentally new four-cylinder engine presented us with the challenge of doing even better. And we succeeded. Not only is the output per litre unrivalled for a turbocharged engine, the high level of efficiency also demonstrates that the internal combustion engine still has further potential," he says.

As with the outgoing M133, two variants of the M139 are planned. In standard form as set to appear in the A45 4Matic, it delivers 265kW at 6500rpm and 480Nm of torque between 4750 and 5000rpm. With greater turbocharger boost pressure and other power-enhancing upgrades, it also endows the more extreme A45 4Matic S with 310kW at 6750rpm and 500Nm of torque between 5000 and 5250rpm.

This provides the new A45 4Matic S with 85kW and 100Nm more than the A35 4Matic and other recently unveiled new AMG compact models, including the A35 4Matic sedan and CLA35 4Matic.

The specific output of the M139 sets new standards for a Mercedes-AMG engine at 155.7kW per litre in its most extreme state of tune. By comparison, the most powerful version of the earlier M133 unit boasts 140.6kWper litre.

Increased torque at higher engine speeds also provides a broader range of revs with the ignition cut out of the M139 placed at 7200rpm compared to the maximum 6700rpm of the M133.

Of the performance hatchback competition, it is the Audi RS3 that comes close to matching the new A45 4Matic’s power output with a turbocharged 2.5-litre five-cylinder engine delivering 298kW at 5850rpm and 480Nm between 1700 and 5850rpm.

The benchmark output of the new Mercedes-AMG powerplant eclipses the 300kW of the turbocharged 2.0-litre four-cylinder engine used by the Mitsubishi Lancer Evolution X GSR FQ400, which was sold by Ralliart in various markets as a series production model with full guarantee back in 2009.

An even more powerful version of the Mitsubishi Lancer Evolution X GSR called the FQ440 was launched in 2014 with an output of 328kW. However, it was offered in very limited numbers and featured aftermarket components, including a bespoke turbocharger, hi-flow exhaust, uprated intercooler and ECU.

The biggest change in engineering philosophy brought to the M139 is its mounting within the engine bay. Sited transversely as with all engines used in Mercedes-Benz’s latest generation of compact models, it has been turned 180 degrees compared to the M260 and earlier M133 engines in a configuration that positions the intake system at the front and the turbocharger and exhaust manifold at the rear.

The revised mounting is claimed to provide improved air ducting with shorter distances between the inlet manifold and the engine and between the engine the turbocharger - a development that manifests itself in improved throttle response, according to AMG.  It also permits improved packaging; the overall height of the engine is lower and more efficiently housed within the engine bay than before for greater heat dissipation and improved cooling properties.

In a development borrowed from the latest evolution of its V8 engine, AMG has also provided its new four-cylinder with a twin-scroll turbocharger featuring roller bearings in a move it says helps to reduce mechanical friction and increase response. A new electronically controlled wastegate is also claimed to allow the turbocharger boost pressure, which peaks at 2.1 bar, to be controlled more precisely when accelerating from partial throttle loads.

In a further departure from the M260 and M133 engines, the M139 also features a brand new cylinder head with injection nozzles and spark plugs that are positioned at a greater angle than before. The new design is claimed to enlarge the exhaust valves and provide greater combustion efficiency by allowing gases to stream out of the chamber at greater speed and with lower losses than previously.

The valves are controlled by two overhead camshafts that operate via roller cam followers. Adjustment is on both the inlet and outlet side via a heavily reworked version of the Camtronic valve control system used on the M260 engine. Mercedes-Benz’s performance car division claims to achieved improved low-end responsiveness, added fuel efficiency at middling revs and greater power at the top end through the adoption of new cam geometries.

The new engine also receives revised water jacket geometry which permits a faster flow rate via a demand-controlled electric water pump for improved cooling properties, according to AMG. A corrugated metal seal isolates the cylinder head from the crankcase.

For the first time on a Mercedes-Benz production engine, the M139 also uses two-stage fuel injection. The first stage of injection takes place within the combustion chamber with newly developed piezo injectors operating at up to 200 bar of pressure. The second stage taking place within the intake manifold via solenoid valves. The compression ratio has also increased from 8.6:1 to 9.0:1.

In a development already adopted on the M260 engine, the M139 also receives a particulate filter as part of a heavily revised exhaust system.

Editor:Greg Kable