Mercedes-AMG shares the secrets behind the most powerful 4-cylinder engine in the world

Mercedes-AMG uses the internal designation M 139 for its 2.0 Turbo engine producing 421 CV, which becomes the most powerful series-production 4-cylinder. Here are its key figures.

Where is the limit? Mercedes-AMG pushes it even further, reaching 310 kW (421 CV) with its new 2.0 Turbo engine, internally designated M 139, which replaces the previous M 133. That is 30 kW more, an increase of 40 CV in peak power, keeping it at the very top of the performance rankings among series-production 4-cylinder engines. Its destination? The upcoming Mercedes A45 AMG and CLA 45 AMG.

In its most powerful version, the 2-litre Mercedes reaches 421 CV and a peak torque of 500 Nm, although a second variant with 387 CV will also be offered, with peak torque at 480 Nm. These are figures that not long ago could only be found in very large-displacement V8 engines.

Specific output of 211 CV per litre

Yes, the calculation is simple, and the result speaks for itself. We are talking about a specific output of 211 CV per litre of displacement, and the ability to rev up to 7,200 rpm. These are figures that many supercars cannot match, and that are almost typical of racing engines. But what does this 2-litre from the brand with the star need to achieve such performance?

First and foremost, turbocharging with a twin-entry turbocompressor, which other manufacturers call “Twin Scroll”. Not to be confused with a twin turbo. Here, two separate channels direct the exhaust gases to the turbine so that the pulses do not interfere with each other during the intake and exhaust cycles. This measure not only improves power, but also low-rev response.

Another additional improvement in the turbocharger is that the turbine spins on bearings, a solution inherited from the V8 of the AMG GT Coupé. The maximum rotational speed the turbine can reach is 169,000 rpm.

Compared with its predecessor, it is also worth highlighting that Mercedes has completely rotated the engine’s mounting position, so that the turbocharger and exhaust manifold are now at the rear of the engine, and the intake is at the front. The aim is to improve air flow and allow a flatter front end, which benefits aerodynamics.

The maximum boost pressure reaches 2.1 bar, it features an electronically controlled wastegate valve, and turbo cooling is mixed, using both water and oil.

Other technical solutions used in the 2.0 engine of Mercedes-AMG include the “closed-deck” block design, derived from racing engines, for greater rigidity. The pistons are forged aluminium, and the cylinder liners are coated with Nanoslide, a treatment that reduces friction losses, as found, for example, in Mercedes AMG Formula 1 engines.

The new cylinder head configuration allows the use of larger exhaust valves, and for the first time in a 4-cylinder, a two-stage injection system is used: direct injection into the combustion chamber at pressures of up to 200 bar via piezoelectric injectors, and indirect injection into the intake manifold, controlled by solenoid valves.

The “crowning touch” is a sophisticated cooling system, with an additional radiator located in a side fin, and a secondary low-temperature circuit for the intercooler. The coolant is circulated by a high-power electric pump.

The Affalterbach factory of Mercedes: one man, one engine

As could only be expected, each new engine is hand-assembled by AMG specialists, following the “One Man, One Engine” principle. Although the term “hand-built” may sound odd when we are also talking about a production area fully integrated into Industry 4.0 methods.

More than a factory, the engine hall looks like an operating theatre, as you can see in the following video. The workers even have digital assistance, tools connected via Wi-Fi, and the help of autonomous transport trolleys.

Of course, every M 139 engine carries the AMG plate identifying the technician who was responsible for its assembly.