What's the news?
Mercedes-AMG is claiming that its new 'M139' 2.0-litre turbocharged motor is the world's most powerful four-cylinder engine in series production - as it can deliver up to an astonishing 416hp in its 'S' guise.
Developed from the M133 engine that was found in the old Mercedes-AMG A 45, the M139 is surely destined for the A 45's successor first and foremost, as there's already the 306hp A 35 in that model's line-up.
The M139 turbo four delivers 208hp-per-litre in its most potent form, although a 382hp 'base' version is still 1hp to the good compared to the old M133. Torque is 480Nm from 4,750-5,000rpm in the base M139, with the S churning out 500Nm from 5,000-5,250rpm. Mercedes-AMG also says it is more 'free-revving' than the old motor, with a 7,200rpm rev limiter testament to that.
There are some tasty engineering tricks at play here, to make the M139 such a powerful unit. It is still transversely mounted, but - compared to the engines in either the current A 35 or the old A 45 - the turbo and exhaust manifold are now at the back of the lump, closer to the front bulkhead of the passenger compartment. That means the intake system is positioned at the front, allowing for 'the flattest possible and aerodynamically advantageous' front-section design. The twin-scroll turbocharger features roller-bearings for the first time, to improve responsiveness, while there's an electronically controlled wastegate to optimise the flow of gases. Even the M139's all-aluminium crankcase is a chill-cast item, which means it's a very high-strength component.
After it finds its way into the A-Class hatchback, expect the M139 to make an appearance in the A-Class Saloon, the CLA, the CLA Shooting Brake and any yet-to-be-announced successor to the old GLA 45 AMG.
Anything else?
"We already set the benchmark in the segment with the preceding engine," said Tobias Moers, chairman of Mercedes-AMG. "This fundamentally new four-cylinder presented us with the challenge of doing even better. And we succeeded with a number of sometimes revolutionary solutions. With the M139, we have once again impressively demonstrated the engine expertise of Mercedes-AMG. 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."