New B58 m40i/m50 posts 0‑60 in 4s

BMW’s B58 straight-six is having another moment. That matters because this engine is basically the center of BMW’s non-full-M performance lineup — the cars people buy when they want real speed without the compromises of an M3 or M4. The gap, until recently, was that these “sweet spot” models were already good but not obviously moving forward in a big way. Now they are. BMW has rolled a revised B58 into newer M40i and M50-badged cars, and the results are concrete: more output on paper, quicker real-world testing, and the same everyday usability. (press.bmwgroup.com) ### What actually changed in the engine? The new version is the B58B30M2 — still a 3.0-liter turbocharged inline-six, but now paired more tightly with 48-volt mild-hybrid hardware. In BMW’s own 2025 3 Series and 4 Series update material, the company framed the change around sharper (press.bmwgroup.com)he revised setup is rated at 386 hp and 398 lb-ft. (press.bmwgroup.com) ### Why are people talking about “4-second” 0–60 runs? Because at least one of the first cars using the newer setup has already hit that mark in instrumented testing. MotorTrend tested the 2025 BMW X3 M50 — the SUV successor to the old X3 M40i idea — and got 0–(press.bmwgroup.com)e has real headroom when launch control, traction, and conditions line up. (motortrend.com) ### Is this the same story for the M440i? Not quite — and this is the catch. The current North American M440i already uses the updated B58 with mild-hybrid help, but published tests for the convertible still land around 5.0 seconds to 60 mph, which makes sense because it is heavier and, in some trims, rear-dr(motortrend.com)vetrain, and launch conditions. (grassrootsmotorsports.com) ### What about the M50 badge? BMW is using M50 as the new top rung for some M Performance models, especially in the latest X3. That badge change is not just marketing fluff. In the X3’s case, the M50 replaces the M40i and comes with a stronger version of the formula — 393 hp and 428 lb-ft from th(grassrootsmotorsports.com)ut the newest, most aggressive non-full-M application of this engine. (press.bmwgroup.com) ### Is the efficiency claim real? Partly, yes — but it needs calibration. BMW’s U.S. specs page for the M440i xDrive Gran Coupe lists 28 mpg combined, not mid-30s mixed driving. That means claims around “35 mpg” are probably anecdotal highway or trip-computer numbers, not the offici(press.bmwgroup.com)t it is not suddenly a Prius with launch control. (bmwusa.com) ### Why does this matter beyond one engine? Because BMW keeps proving there is still room to improve the classic fast daily-driver recipe. The B58 was already one of the company’s best modern engines. The revised version keeps the smooth s(bmwusa.com)nto harsher, pricier full-M territory. That is the real story. (press.bmwgroup.com) ### So what’s the bottom line? The new B58 update is not one miracle number. It is a broader upgrade path across BMW’s M Performance lineup. In the lighter, grippier applications, it can absolutely deliver 0–60 in about 4 seconds. In cars like the M440i, the gain is more about sharp(press.bmwgroup.com)gine even harder to argue with. (press.bmwgroup.com)