Why the Next BMW M3 (G84) Will Skip PHEV: A Mild-Hybrid Revolution

Yesterday, Frank van Meel, CEO of BMW M, confirmed what we’ve been writing about for months: the next-generation BMW M3, codename G84, will retain its straight-six engine and be launched alongside the iM3 ZA0 EV. He mentioned in an interview that the M3 will continue to use a six-cylinder 3.0 liter engine, but he stopped short of confirming which engine variant will that be. One thing is clear though: The G84 M3 won’t be a PHEV like the larger M5. Instead, according to our sources, BMW will introduce a 48-volt mild-hybrid system—a more refined approach for a performance-focused sports sedan.

Why No PHEV for the M3?

There are several reasons why the M3 won’t follow the M5’s plug-in hybrid path. Firstly, the addition of a large battery pack would significantly increase the vehicle’s weight, which could compromise the M3’s agility and dynamic handling characteristics. Weight management is a key factor in keeping the M3 true to its motorsport roots, and adding a bulky battery system would undermine this essential quality.

Secondly, the customer base for the M3 differs from those who might choose a plug-in hybrid for daily electric driving. M3 owners typically prioritize performance and excitement over all-electric daily driving. A good comparison is the customer profile for the new Porsche 911 hybrid, which focuses on performance over electric range—a mindset shared by BMW M3 buyers.

Lastly, the packaging constraints play a pivotal role. The M3 is obviously smaller than the M5, making it challenging to incorporate the complex mechanicals of a PHEV without compromising interior space and balance. A PHEV setup would require not only room for a battery pack but also additional cooling and electrical infrastructure, which are easier to accommodate in the larger M5.

The Mild-Hybrid Approach

Instead of going the PHEV route, BMW will equip the next G84 M3 with a 48-volt mild-hybrid system. Mild-hybrid technology works by providing supplementary electric assistance to the internal combustion engine, particularly during coasting, and enhancing functions like automatic start-stop. However, unlike a PHEV, a mild-hybrid system cannot operate independently from the combustion engine.

BMW’s mild-hybrid technology brings several advantages to the M3, including the highly publicized “eBoost” function. This feature delivers additional horsepower with minimal lag, utilizing the 48-volt power supply and starter motor to enhance acceleration. The generator, powered by a lithium-ion battery, is cleverly integrated into the engine’s belt drive, ensuring smooth power delivery. This system doesn’t transform the M3 into a hybrid powerhouse but enhances performance with minimal weight gain, staying true to the car’s Ultimate Driving Machine slogan.

The Engine Question: S58 or B58?

One of the biggest uncertainties surrounding the next-gen M3 is the engine choice. The current M3 is powered by the S58 twin-turbocharged 3.0-liter straight-six engine, but it has not yet been certified for the upcoming Euro 7 emissions standards, set to take effect in mid-2025. There is also the B58 3.0 liter which already has the 48 volt mild-hybrid integration, and it’s used, successfully, across various M Performance BMW models.

From a business standpoint, the B58 could make sense, as it’s widely used in models like the M240i, M340i, Z4 M40i, and Toyota Supra. A 48-volt mild-hybrid B58 would also be more cost-effective, but this decision could frustrate hardcore M enthusiasts. The last time BMW placed a non-M engine in an M car—the N55 in the F87 M2—it sparked considerable debate, despite the engine’s solid performance.

Choosing the B58 might make financial sense, but it could be seen as a step backward by purists. If BMW goes with the S58, they will need to ensure the engine is Euro 7-compliant, and luckily there is plenty of time to get the engine ready for a 2027-2028 M3 launch. Either way, BMW has a challenge on its hands as it balances emissions compliance with the expectations of M3 enthusiasts.

A Track-Ready Mild-Hybrid M3

One thing is certain though: BMW won’t compromise on the M3’s track capabilities. If the B58 is selected, it will likely be a high-performance variant designed to withstand extended track times and deliver the sharp driving dynamics M cars are known for. The 48-volt mild-hybrid system will enhance performance, not water it down, ensuring the next M3 delivers on its reputation for being a true driver’s car.

With an expected power output of 530-560 horsepower, the mild-hybrid M3 will offer thrilling performance while meeting stricter emissions standards. The drivetrain won’t match the output of the M5’s PHEV system, but it will provide the perfect balance between power and weight, keeping the M3 a true benchmark in its segment.

Luckily, BMW won’t go down the AMG route with a four-cylinder hybrid.