This new engine could revolutionize a lot of automotive segments along the way

Mercedes-AMG has revealed an all-new 2.0-liter turbocharged inline-four engine that, at least as far as output goes, is poised to become the most powerful series-production four-cylinder engine in the world. It’s called M 139 and as far as specs are concerned, its output - as much as 416 horsepower and 369 pound-feet of torque — is an absolute doozy. The staggering figures translate to a specific output of 208.9 horsepower per liter, higher than what you can expect to get from today’s supercars. Then again, Mercedes-Benz and its in-house performance arm, Mercedes-AMG, are known for being at the forefront of innovation. This isn’t anything new, except the actual engine, which we’ll eventually see on the automaker’s next generation of “45” models, including the A 45 Sedan, GLB 45, CLA 45, and CLA 45 Shooting Brake.

The new Mercedes-AMG M 139 four-cylinder engine - why it matters?

This is a big deal. It’s a really big deal. Imagine, for a second, driving a 2017 Mercedes-AMG CLA 45 Sedan. You’re feeling good about yourself because you’re driving a car with a potent 2.0-liter bi-turbo four-cylinder engine (M 133) that produces 375 horsepower and 350 pound-feet of torque. Those numbers represent a 20-horsepower and 18-pound-feet-torque increase from its predecessor, which Mercedes-AMG achieved by adding a new exhaust camshaft and a tuned ECU unit into the equation.

The power increase helps the 2017 AMG CLA 45 sprint from 0 to 60 mph in 3.8 seconds on its way to a capped top speed of 155 mph. Impressive numbers all around, but what if I told you that the new AMG CLA 45, as well as its “45” brethren, is going to be faster and more powerful than you ever imagined. Well, it’s less of a possibility and more of an inevitability now that Mercedes-AMG has unveiled its new M 139 four-cylinder engine.

Mercedes-AMG M 139 four-cylinder engine - by the numbers

Want to Know How AMG Builds a 416-Horsepower Engine? See For Yourself
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Consider the numbers first: the new 2.0-liter turbocharged four-cylinder engine has been engineered to produce 382 horsepower at 6,500 rpm and 354 pound-feet of torque from 4,750 to 5,000 rpm. That’s seven horsepower and four pound-feet of torque more than a more dated and revamped engine. Throw in the “S” nomenclature on any of the models that will carry this new four-banger and the output increases to a whopping 416 horsepower at 6,750 rpm and 369 pound-feet of torque from 5,000 to 5,250 rpm.

It’s hard to rationalize the true value of these numbers without the proper context. So, let’s compare the current Mercedes-AMG CLA 35 with some of its most notable rivals. Two models immediately come to mind. The Volvo S60 Polestar, for example quietly packs its own 2.0-liter turbocharged four-cylinder engine that produces 362 horsepower and 347 pound-feet of torque. The BMW M2 Competition’s engine produces more power — 405 horsepower and 406 pound-feet of torque — than Mercedes-AMG’s new M 139 four-cylinder unit, but Bimmer’s using a six-cylinder engine in its own performance machine.

A 2.0-liter turbocharged four-cylinder engine that can approach — and exceed — 400 horsepower is unheard of in its segment. But that’s exactly what Mercedes-AMG has come up with. The M 139 engine isn’t just new, but it’s also the most powerful series-produced four-cylinder engine in the world. And you know the best part? The Mercedes-AMG CLA 45 isn’t the only model that benefit from this new powertrain; it will also be used on models like the AMG A 45, GLB 45, and the CLA 45 Shooting Brake. If you see Mercedes-AMG flexing, that’s because it has every right to do so.

Before it can do that, though, there’s that matter of actually building the world’s most powerful turbocharged four-cylinder production engine. The process of building this engine is tedious and meticulous, in part because it’s built entirely by hand in the automaker’s facility in Affalterbach, Germany.

Mercedes-AMG M 139 2.0 litre turbocharged four-cylinder engine specifications
Displacement 1991 cc
Bore x stroke 83.0 x 92.0 mm
Output 310 kW (421 hp) at 6750 rpm (S-model) 285 kW (387 hp) at 6500 rpm (basic version)
Peak torque 500 Nm at 5000-5250 rpm (S-model) 480 Nm at 4750-5000 rpm (basic version)
Max. engine speed 7200 rpm
Compression ratio 9.0:1
Turbocharging One twinscroll turbocharger with roller-bearing compressor and turbine wheels
Max. charge pressure 2.1 bar (S-model) 1.9 bar (basic version)
Mixture formation Combined direct and manifold injection. 1.) Third-generation multiple direct injection. Fast and precise piezo injectors spray the fuel into the combustion chambers at high pressure 2.) Additional intake manifold injection with solenoid valves
Cylinder head Two overhead camshafts, 16 valves, adjustable intake and exhaust camshafts, CAMTRONIC valve timing adjustment for the exhaust camshaft
Max. air mass throughput 1,200 kg/h (S-model) 1,100 kg/h (basic version)
Engine weight (wet) 160.5 kg

How is Mercedes-AMG’s M 139 engine different?

Want to Know How AMG Builds a 416-Horsepower Engine? See For Yourself
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Power output notwithstanding, the new four-cylinder engine also differs in some ways compared to the earlier turbo-four unit. For starters, the M 139 engine comes with a new twin-scroll turbocharger that’s fitted with roller bearings. This is the first time Mercedes has adopted this design, in part to reduce any form of mechanical friction that would have prevented the turbo to spin as easily as it should. That’s not an issue anymore with the roller bearings as the turbo can now spin more easily. Mercedes also divided the turbine housing and the exhaust manifold so the exhaust flow can be separately fed into the turbine. You’re going to read the word “smooth” a lot in this area, but it’s the best way to describe the unique makeup of this engine. A lot of how Mercedes designed the M 139 engine comes as a result of figuring out smoother ways for the engine to function to its full potential. Take the wastegate as an example. It’s now electronically controlled, which not only improves its own responsiveness, but also offers more precise control of the intake pressure.

Mercedes also applied a handful of methods and technologies it learned from motor racing. This shouldn’t come as a surprise considering AMG’s heavy involvement in creating the M 139. There’s the ducted engine cover, which transfers air to the turbo housing. It also looks like an air deflector that’s similar to the one found on the AMG GT’s 4.0-liter twin-turbo V-8 engine. Even the composition of the engine block is race-derived. It’s made from chill-cast aluminum, which is created through a process that involves pouring molten aluminum into a water-cooled metallic mold that cools and solidifies quickly. The whole process of creating the engine block translates into a dense, high-strength structure that’s similar to the engines that are typically used on race cars. It’s meant to withstand a lot of wear and tear while also allowing higher peak combustion pressures.

Want to Know How AMG Builds a 416-Horsepower Engine? See For Yourself
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The M 139 engine uses AMG’s Nanoslide cylinder coating, which is also used in Mercedes’ Formula 1 cars, as well as the bigger 6.2-liter V-8 M 156 engine that’s being used by the upper echelon of AMG models. The coating endures minimal friction in the cylinder linings, ensuring that they’re not subjected to the wear and tear of inferior components.

The M 139 engine is also the first AMG four-cylinder engine to use port and direct fuel injection, a necessary move to achieve its impressive output. There’s also a new engine cooling system that’s made up of more radiators than past engines. There’s one in the wheel arch, which joins the all-too-recognizable frontal radiator and the air-to-liquid intercooler. A variable speed electric bump is responsible for circulating coolant into these heat exchangers while the air-cooled ECU is strategically placed on the housing for the air filer. Likewise, the engine’s coolant circuit is responsible for keeping the transmission fluid from getting too hot. If the coolant circuit needs an assist of some sort, a heat exchanger mounted on the transmission comes in for the assist.

Final Thoughts on the Mercedes-AMG M 139 engine

Want to Know How AMG Builds a 416-Horsepower Engine? See For Yourself
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If all of this sounds complicated, it’s because the development of this engine was exactly that: complicated. Neither Mercedes nor AMG got to this point without understanding the steps it needed to take and the process it needed to follow to build an engine that’s capable of redefining its segment. The M 139 engine isn’t just a new engine; it’s a groundbreaking engine for Mercedes-AMG, especially now that it’s about to unleash the new wave of AMG 45 models that will get first dibs on the new powertrain.

The Mercedes-AMG A 45 hatchback technically gets the first crack at the engine since it’s already scheduled to debut in a few months. From there, we can expect the M 139 to find its way into the next-generation AMG CLA 45, as well as the next-generation GLA 45 and GLB 45 crossovers. For now, Mercedes-AMG plans to pair the powertrain to a nine-speed dual-clutch automatic transmission and an advanced all-wheel-drive system with its own “Drift” setup. Whether that translates to some rollicking tire-burning sessions remains unclear, but for now, we can take comfort knowing that Mercedes-AMG has a new engine that could redefine our own expectations on what an AMG model can do, both on the road and on the track.

Good times ahead? You better believe it.

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