Autocar has been told the M139 engine will adopt a 48V integrated starter motor similar to that already used by the turbocharged 3.0-litre in-line six-cylinder M256 unit, which powers the CLS 53 4Matic+ and other recent new AMG models.
In the CLS 53 4Matic+, the gearbox-mounted starter motor provides an additional 22bhp and 184lb ft of electric boosting. In the next C63, however, it is set to be tuned to provide significantly more power in combination with a similar torque loading.
The new EQ Boost hybrid drivetrain is also planned to run in combination with Mercedes’ nine-speed torque-converter MCT Speedshift gearbox.
The entire C-Class range is powered exclusively by electrified four-cylinder engines, with plug-in and mild-hybrid technology rolled out across the range for better efficiency and thus reduced emissions.
One of the most significant advantages in the adoption of the new electrified driveline is a reduction in weight over the front axle of the new C63 4Matic. At 160.5kg, the M139 four-cylinder unit weighs 48.5kg less than the M177 V8 engine used by today’s C63 4Matic. Even with the addition of the hybrid architecture, including a disc-shaped electric motor and power electronics, the overall weight of the new powerplant is claimed to undercut that of today’s unit.