Mercedes-AMG is preparing to phase out the high-performance four-cylinder plug-in hybrid powertrain used in the C63 S E Performance and GLC 63, marking a significant reversal in the brand’s electrification strategy. Speaking with Autocar at the unveiling of the all-electric Concept AMG GT XX in Germany, a senior AMG insider has allegedly confirmed that the M139-based hybrid will be replaced by either an updated inline-six or an all-new V8.
Downsizing Didn’t Deliver
The M139 2.0-liter engine, which debuted in 2022 with a combined system output of over 670 horsepower, was developed to help AMG comply with emissions regulations while preserving performance credentials. But the downsized, electrified setup never caught on with the brand’s core audience. Critics pointed to its muted sound, high curb weight, and lack of emotional character compared to the previous 4.0-liter V8. Despite strong output and advanced engineering, the system added complexity without delivering the kind of visceral experience buyers expect from AMG models. Making matters more difficult, the M139 powertrain would require expensive reengineering to meet upcoming Euro 7 emissions regulations. That looming cost has reportedly sealed its fate.
Return to Larger Engines
Instead, Mercedes-AMG is preparing to reintroduce more traditional performance engines. A revised 3.0-liter inline-six—already in use in models like the GLE 53 and CLE 53—is one candidate for future C-Class and SL models. A new V8 with a flat-plane crankshaft, inspired by the AMG GT Black Series, is also allegedly in development. Both options will feature hybrid assistance in some form, either through 48-volt mild-hybrid systems or full plug-in setups.
BMW M’s Strategy Pays Off
The move stands in stark contrast to BMW M’s engine philosophy. While AMG pursued a radical shift toward smaller-displacement hybrid engines, BMW M opted to evolve its proven 4.4-liter twin-turbo V8—now used in the new 2025 BMW M5, the XM, and high-performance SUVs like the X5 M and X6 M.
Instead of downsizing, BMW chose to pair its V8 with electrification. The new M5, for example, delivers 717 horsepower and 738 lb-ft of torque from a plug-in hybrid setup built around the V8. The result: regulatory compliance, blistering performance, and the kind of engine note and throttle response buyers expect. That consistency appears to be paying off. While AMG customers voiced frustration with the hybrid four-cylinder’s lack of character, BMW M retained customer trust by sticking with what works. [Source: Autocar]
