Heres How Mercedes got 442 Horsepower out of their 4 Cylinders

According to roadandtrack

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 V8, 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.

AMG’s 53-series cars use what’s called an electric auxiliary compressor, where an electric motor spins up a compressor wheel to feed air into either the turbocharger or the engine directly. The difference between the electric auxiliary compressor and this electric turbocharger is that the compressor doesn’t take in any exhaust air to spin the compressor. Think of it as a turbocharger that uses an electric motor instead of a turbine and a shaft. An electric auxiliary compressor is great at providing quick hits of boost to improve transient behavior, but it doesn’t do much at high engine speeds. The MGU-H installed in the M139 provides similar benefits in transient response and at low engine speeds, but it also provides good power when you get higher up the rev range. Plus, the packaging is simpler here because you’re using one device (the MGU-H) instead of two (the electric auxiliary compressor, and a traditional exhaust-gas turbocharger).

In order to make this electric turbo work, however, you need a high-voltage electrical system. AMG’s upcoming E-Performance models have an Electric Drive Unit (EDU) on the rear axle, which consists of a 6.1-kWh battery and an electric motor that drives the wheels via a two-speed gearbox. (You can read more about this system here) The electric motor spinning the turbocharger shaft gets power from that rear-mounted battery.

AMG says that this 442-hp four-cylinder can be combined with an EDU offering up to 201 hp for short bursts, and 94 hp of continuous power. That doesn’t mean that the C63 successor will have 643 horsepower, though because AMG might further limit the power of the electric motor. All Mercedes will say is that the next AMG C-Class equipped with this E Performance powertrain will offer better power and torque figures than the V-8 it replaces. But, Mercedes also seems to imply that future models beyond this upcoming C-Class will use this four-cylinder hybrid powertrain as well, perhaps approaching that 643-hp figure.

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