The Mercedes M139 Is The Most Powerful Production 4-Cylinder, But That Hasn't Made It Universally Popular

Mercedes-Benz's idea of plonking a 2.0-liter turbo-four into a C63 and giving it a ton of electrical oomph hasn't gone well. When the engine — internally called M139 — debuted in 2019, it had already secured the title ofthe world's most powerful production inline-four by making up to 416 horsepower in its non-hybrid version. And it furthered its lead in 2023 when Mercedes-AMG cranked that number up to 469 hp and, now known as M139l, it ended up in E-Performance models like the GLC 63.

But while the M139l's electric turbocharger and the M139's combinination of direct and port fuel injection, along with its use of Nanoslide cylinder coating, made the four-pot incredibly sophisticated, fate had something else in mind. Mercedes is walking back the four-cylinder C63 and GLC 63. Autocar UK reported that according to a company insider, despite the M139's advanced abilities, "it failed to resonate with our traditional customers." So the German automaker is shifting its strategy to the inline-6 and V8, although hybridization will not disappear entirely.

Mercedes is also phasing out many other compact models that use the engine. In an interview with Edmunds, Mercedes-AMG boss Michael Schiebe cited stricter future Euro 7 emission regulations as a hurdle to carrying it forward. According to Autocar's source, compliance with the new norm would require significant investment. It wouldn't make sense for the company to keep pouring resources into the M139 when they could be deployed elsewhere, like the new S-Class' Euro 7-compliant flatplane-cranked V8 — the M177 Evo.

The main reason enthusiasts and some publications never liked the C63's and GLC 63's E-Performance versions was their lack of character, or more precisely, the missing sound and soul of a V8. As Car and Driver found out in a 2024 C63 test, the M139 sounded buzzy and thin. And while the car made bold headline figures on paper (671 hp and 752 pound-feet of torque), they didn't translate to a meaningful performance upgrade because of the added weight it brought along. This is not a one-off: Edmunds tested the C63 against a 543-horsepower BMW M3 CS, and it didn't go well for the four-pot AMG — the Mercedes' 859-pound weight disadvantage played a tangible role in its performance.

That said, Car and Driver praised the same M139 power plant in 2020 for its "charismatic engine note" when it was used in the AMG CLA45 without the hybrid-ness. Across the pond, Car Magazine had positive things to say about the M139-powered A45's exhaust sound. And Top Gear lauded the M139 for its technical prowess, adding that it was "a monster of a thing ... parping and whistling like a performance motor should."

So it's fair to assume that it wasn't necessarily the engine's fault, but the application that ruffled a few feathers. And perhaps the weight, too.