With up to 421 hp, Mercedes-AMG’s M139 is the most powerful four-cylinder production-car engine in the world. Right now, the M139 is available in 45-series AMG models—we get the 382-hp CLA 45 and GLA 45 in the U.S.—but it will soon arrive in the successor to today’s C63. Yes, the beloved AMG C-Class is getting a 2.0-liter turbo-four in place of a V-8, but thankfully, there won’t be a sacrifice in power. AMG has managed to squeeze 442 horsepower out of its turbo-four, and in the C63, it’ll be paired with a plug-in hybrid system.
Four-hundred forty-two horsepower is scarcely believable from a four-cylinder, but AMG managed it with the adoption of an electric turbocharger. In operating principle, this is the same thing as the Motor Generator Unit-Heat (MGU-H) used in Formula 1. In this instance, AMG installed a 6kW electric motor that spins the shaft that connects the turbine and the compressor up to 156,000 RPM. This effectively eliminates turbo lag, as the electric motor can get the compressor forcing more air into the combustion chamber far more quickly than the exhaust-gas-driven turbine on its own. Transient response is also improved because when the throttle is closed, the electric motor keeps the turbo spinning even though there’s less air flowing out the exhaust. AMG engineers say this new system allows for much more precise control of boost levels, too, because the electric motor provides exact information on turbo shaft speed. For the full story, check out this article from Road & Track.