The inline-six engine doesn’t make many appearances in sedans anymore. The last mass-market holdout is the BMW 3 Series, which has sported one for most of its life. Now, Mercedes-Benz is planning on introducing an all-new inline-six mill in the upcoming C 53 AMG model, making it the first C-Class to sport such an engine since 1997. Currently, the new nameplate’s competition is shaping up to be the incoming BMW M350 xDrive.
At present, our only knowledge of what the upcoming C 53 AMG actually looks like is through spy photos, but the German automaker has confirmed the straight-six’s reintroduction regardless. The C 53 will act as the successor to the current C 63 AMG, a model that uses a turbocharged four-pot. It seems there’s a change in the wind, with enthusiasts clamoring louder and louder for a transition back toward larger engines. Mercedes-Benz seems to be listening.
BMW Has Kept The Inline-Six Kicking
2026 BMW M340i xDrive 50 Jahre Edition front 3/4 angleBMW
When you think of straight-six-powered sedans, one of the only models that comes to mind is the BMW 3 Series. Apart from a few gaps here and there, the nameplate has used the engine type since 1977, when the E21 323i hit the market. The current M340i has kept the tradition alive, and offers enthusiasts a choice between rear or all-wheel drive performance. For those who don’t want to step up into a full M3, the M340i serves as an attractive middle ground.
The straight-six underneath the hood is the fabled 3.0-liter, turbocharged B58, which has also seen use in the modern A90 Toyota Supra. The M340i can chuck out 386 horsepower and 398 pound-feet of torque with the help of a 48-volt mild hybrid system. With all that power at its disposal, the M340i is a large step up over the standard, 2.0-liter turbocharged 330i model.
BMW’s insistence on keeping the inline-six alive, even through these emissions regulation-heavy times, boils down to a couple of things. For one, it can obviously provide a good amount of power — thanks to its two extra pistons — over a four-cylinder engine. At the same time, straight-six engines are inherently smooth, giving BMW’s performance models a healthy air of luxury when not involved in high-performance driving.
BMW carried over its legendary 3.0-liter turbocharged inline-six B58 engine to the updated 3 Series lineup, anchoring the range-topping performance models like the M350 xDrive. Rather than replacing the engine, BMW refined the B58 with its latest Technical Update 2 (TU2) and integrated 48-volt mild-hybrid technology.
2027 BMW M350 xDrive finished in red with black interiorBMW
By pairing the twin-scroll turbocharged engine with an electric motor built into the eight-speed transmission, BMW eliminated initial turbo lag while improving overall fuel efficiency and emissions. The carryover strategy ensures that the 3 Series retains its signature silk-smooth power delivery, tuning potential, and structural reliability while boosting output from 386 to 443 horsepower.
Mercedes-AMG Tried To Make The Four-Pot C 63 Work
2025 Mercedes-AMG C63 S E PerformanceMercedes-Benz
When the current, fifth-generation Mercedes-AMG C 63 hit the market in 2024, the decision to move away from a typical V8 to a turbocharged, plug-in hybrid inline-four was a controversial one. Of course, its 671-horsepower total system output was nothing short of amazing, especially considering its engine only displaced two liters. However, the entire powertrain setup was heavy, complicated, and it deviated quite far from the C 63’s V8-powered heritage.
Mercedes-Benz itself has admitted its mistake with the fifth-gen C 63 AMG. The automaker has stated openly that the attempted formula failed to resonate with its customer base as well as it had hoped, and it made the decision to move away from it. Not to mention, the incoming Euro 7 emissions regulations meant the 2.0-liter PHEV powertrain would need to be overhauled in order to comply. Hence, producing an all-new mill likely proved more financially viable than trying to re-engineer something that few people wanted in the first place.
2025 Mercedes-AMG C 63 S E Performance Fender BadgeMercedes-Benz
With the departure of the turbo-four on the horizon, and a new inline-six on the way, AMG’s course correction sends a wave of delight through the AMG community, as well as the broader gearhead base itself. After years of trying to squeeze more and more power out of smaller and smaller engines, the C 63 AMG went too far in that direction, as evidenced by Mercedes-Benz’s own admission. Now, we can get back to business.
The Six-Pot Is Back For The C 53 AMG
2027 Mercedes-Benz C-Class spy photoCarBuzz/Valnet
While the C 53 AMG has yet to officially arrive, we do know it will use an M256 3.0-liter inline-six shared with the existing CLE 53 and GLC 53 models. When in its CLE 53 AMG application, the mill produces 443 horsepower and 413 pound-feet of torque. Helping the engine along is a small, 48-volt mild hybrid system that injects roughly 23 horsepower into the mix. At the same time, it’s important to keep in mind that the C 53 AMG’s specs could differ, as its performance figures have yet to be confirmed.
The current M256 makes use of an electric auxiliary compressor hooked up to its turbocharger, which is designed to help reduce turbo lag while also supporting a stronger output across the entire rev range. In other words, the boost is spread more evenly throughout the power band. The CLE 53 AMG also offers 4MATIC+ all-wheel drive and a nine-speed automatic, which we may see in the C 53 AMG as well.
Should the incoming C 53 AMG utilize the CLE 53 and GLC 53’s powertrain, it will have a very healthy power advantage over its main rival, the BMW M340i. However, BMW’s M340i is currently on the way out. The new BMW M350 xDrive – the M340i’s replacement – is slated to enter production in November, and is reported to sport 437 horsepower and 428 pound-feet of torque from its revamped B58 3.0-liter straight-six engine. But that’s still less than the Mercedes-AMG might offer.
BMW’s And Mercedes’ Return To Six-Cylinder Engines: Same Formula, Different Reasons
2027 BMW M350 xDrive finished in red with black interiorBMW
BMW never quite left the six-cylinder reservation like Mercedes-Benz did, and yet both marques are entering 2027 with engines sporting six combustion chambers arranged in a row. The C 53 AMG’s likely powertrain setup will emphasize its engine first, with a small mild-hybrid system working in the shadows. This is a stark contrast to the C 63 AMG’s 2.0-liter electrified motor.
But the Mercedes-AMG C 53 will have its work cut out for it. Because BMW never left the straight-six behind, it’s become synonymous with the M340i’s character, and that reputation will likely carry over into the M350 xDrive. The C 53 AMG will have to prove to buyers that it can deliver the sort of driving character that AMG buyers expect, rather than the same electrified feel found in the preceding model.
Performance cars need to be fun and, to a certain extent, visceral. With Mercedes-AMG coming back into the fold after its acknowledged failed C 63 AMG experiment, only time will tell if it can deliver.
Base Trim Engine
2.0-Liter Turbo I4 Plug-In Hybrid
Base Trim Transmission
9-Speed Automatic
Base Trim Drivetrain
All-Wheel Drive
Base Trim Horsepower
671 hp
Base Trim Torque
752 lb-ft
0-60 MPH
3.3 Seconds
Segment
Compact Luxury Performance Sedan
Sources: Mercedes-Benz, BMW, Car and Driver.
