Four hundred and sixteen horsepower from a 2.0-liter four-cylinder. That's 208 hp per liter—a whopping 104 horses per cylinder. That's what AMG has squeezed out of the M 139 engine, the little turbo four that will power the next-generation Mercedes-AMG A45, along with the CLA45 and GLA45.
So how did AMG manage to make the most powerful production-car four-cylinder ever? , the automaker details all the changes that went into this next-generation engine, and for the most part, it's all old-school hot-rodding tricks.
The new M 139 is a development of a previous engine, the 376-hp M 133 that previously held the title of most powerful production four-cylinder. The new version is available in two flavors: a 382-hp, 354-lb-ft base version, and the 416-hp, 369-lb-ft "S" trim.
In order to make this power, AMG switched the intake and exhaust routing. The new transversely-mounted engine has its intake facing front, with the exhaust manifold and turbo nestled against the firewall. This allows for a straighter, less restrictive intake path, and shortens both the intake and exhaust runners.
AMG also crammed bigger exhaust valves into the cylinder heads, repositioning and angling the fuel injectors to make room for larger exhaust ports. This is also the first AMG four-cylinder with both port and direct fuel injection.
Dozens of smaller improvements contribute to the increased output. Roller-bearing turbos, a closed-deck engine block and aluminum crankcase, Nanoslide-coated cylinder bores, and an improved cooling system with an electric water pump all round out the package. And with the M 139, AMG has gone back to its "one man, one engine" assembly method, where each powerplant is assembled from start to finish by a single technician. We can't wait to see what it's like to drive.