Because 416 horsepower from a 2.0-liter four-cylinder is not outrageous enough, apparently.
When Mercedes hit the stage with an upgraded version of the 2.0-liter turbocharged four-cylinder M133 engine that made 375 horsepower in the AMG GLA 45 and CLA 45, the company claimed it had once again broken a record for building the most power-dense engine in the industry. The new M139 makes up to 416 horsepower and 369 lb-ft of torque using the same 2.0-liters as its predecessor, making the new engine's high 208 horsepower-per-liter ratio tough to beat.
However, two questions still remain. Namely, how could Mercedes build a high-performance engine with around 30.5 psi of boost and A: make it reliable enough for daily driving, and B: cut out the bad behavior typical of such heavily boosted engines? Australia's Car Sales got to chat with Mercedes-AMG's head of engine development, Ralph Illenberger, to find the answers.
In regards to durability, Illenberger says that the engine's service life remains the same as its predecessor's, with an expected lifespan of 250,000 kilometers, or about 155,342 miles. Service intervals remain the same, with each one taking place every 12 months or 20,000 kilometers (12,427 miles).
In order to achieve that, Mercedes gave the four-cylinder M139 thicker cylinder walls and a chill-cast closed-deck aluminum crankcase able to withstand combustion pressures of up to 2,320.6 psi, baffle plates that stop oil from sloshing in the stump (necessary considering the M139's low-viscosity 0W20 oil), a new oil cooling system, an on-demand high-capacity water pump, and separate cooling systems for the block and head.
These measures help the engine maintain durability despite the insane stress its components endure. But on the flip side, engines relying on so much boost to hit high horsepower targets can many times feel unnatural. That's why Mercedes tuned the M139 to increase low-end torque, reduce turbo lag, and give the engine a linear torque curve that makes it more fun to dig into the throttle than a flatter torque curve would.
"The torque curve is improved. The old one was flat and like a diesel. The new one offers more torque at lower rpm – it's no longer flat but shaped," said Illenberger. "There's pretty good acceleration at 1500 rpm. Acceleration at 3500 rpm is much better. You'll notice improved driveability and it revs further too."
Accomplishing that meant giving the engine a larger twin-scroll turbocharger and better bearings, allowing it to spin up to 169,000 rpm, as well as adding "torque filling" strategies that include both direct and manifold injection as well as electronic wastegates that allow more control over boost pressure than pneumatic units would.
But the most exciting news comes from what Illenberger said about the engine's future. "There will be more to come," he said. "There's always room for improvement. But 416 hp is really quite a high number, especially when it's also street-legal. That was the challenge. We'll see what the future will bring." Suffice it to say, it's impressive that AMG is still trying to find ways to get more horsepower out of such a small engine.