BMW B58 Gets a 392-HP Boost: Is the M340i the Sweet Spot?
You know that feeling when your favorite recipe gets a little extra kick, and suddenly it’s even more addictive? That’s exactly what happened in 2025 when BMW decided to spice up the B58 3.0-liter TwinPower Turbo straight-six in the M340i, M440i, and M240i. Even though we’re already well into 2026, I still can’t stop thinking about how this subtle power bump reshaped the M Performance lineup. Why? Because sometimes the best upgrades aren’t about massive horsepower wars—they’re about perfecting the balance between daily drivability and straight-up grin-inducing acceleration.
Let’s rewind to late 2025. BMW quietly dropped a mid-cycle update, and the M340i xDrive was the first to benefit. The sedan and the Touring wagon both woke up with 392 horsepower and 398 lb-ft of torque—that’s an extra 18 hp and 30 lb-ft compared to the pre-update models. Does 18 horsepower sound like pocket change? Maybe, if you compare it to a monster like the M3 Competition. But here’s a fun fact: that bump is literally the output of a standard walk-behind lawnmower. You’re now carrying a whole lawnmower’s worth of extra shove under the hood, but you’d never guess it from the polished cabin or the seamless way the eight-speed automatic delivers the goods. The 48-volt mild hybrid system still chips in with 12 hp, so the overall package feels more urgent than the numbers suggest.
So what does all this translate to on the road? The 0-60 mph sprint drops from 4.4 seconds to 4.3 seconds. Yeah, it’s just one-tenth of a second, but when you’re waiting at a stoplight and that guy in the Mustang GT next to you thinks he’s got you beat, trust me—that tenth makes a difference. It’s also a nice little psychological win because the M340i now sits as the second-most-powerful B58-powered BMW, just one horsepower shy of the X3 M50’s 393 hp total (though the SUV still packs a thicker torque curve at 428 lb-ft). Even cooler? This sedan now boasts more than double the power of the legendary road-legal E90 touring car, and it’s only 8 hp down on the revered E39 M5. Let that sink in: your executive express is breathing down the neck of an all-time great.
What about the M440i and M240i? Those of us who love the 2 Series coupé or the 4 Series Gran Coupé had to wait a bit longer. BMW said the same 392-hp upgrade “will in future” arrive for the M440i coupe, convertible, and four-door, as well as the entry-level M240i. Well, “future” became a reality later that year, and now you can grab an M240i with the same heart. The delay was a little annoying, sure, but good things come to those who wait—especially when you’re talking about a compact rear-wheel-drive platform with nearly 400 hp on tap.
Here’s where it gets genuinely surprising: more power often means worse fuel economy, right? Not this time. The updated B58 is actually a greener animal. The M240i’s consumption, for example, improved from 8.8 L/100km (26.7 mpg) to 8.0 L/100km (29.4 mpg) under WLTP. The 4 Series variants see similar love, with the Gran Coupé sipping just 7.8 L/100km (30.1 mpg). The real hypermiler award goes to the M340i sedan, though—it chills at 7.5 L/100km (31.3 mpg), while the Touring trails at 7.9 L/100km (29.7 mpg). How does BMW pull this off? Smarter boost management, revised engine mapping, and the mild hybrid system working harder to fill in torque gaps while coasting. It’s the kind of efficiency that makes you wonder: when was the last time you could legitimately use “fun” and “green” in the same sentence without a hybrid badge?
| Model | Horsepower | Torque (lb-ft) | 0-60 mph | WLTP Consumption (L/100km) |
|---|---|---|---|---|
| M340i xDrive | 392 | 398 | 4.3 s | 7.5 (sedan) |
| M440i xDrive | 392* | 398* | TBC | 7.7 (coupe/convertible) |
| M240i xDrive | 392* | 398* | TBC | 8.0 (coupé) |
| X3 M50 xDrive | 393 | 428 | 4.4 s | 8.5 (est.) |
*Post-update figures; note that North American rear-wheel-drive models might show slightly different ratings.
While we’re geeking out over the powertrain, BMW also tossed in a few cosmetic and tech updates. The My BMW App got a Charging Guide for EV owners, which feels a bit like bringing a salad to a barbecue, but it’s a solid move for the i4 and iX crowd. More importantly, if you’re ordering a 2 Series Gran Coupé, you can now spec Cape Yellow Green paint—a shade that’s basically “choose me” in pigment form. And the 4 Series Gran Coupé and i4 finally received those snazzy laser rear lights, which are essentially adaptive LED taillights that adjust their beam pattern based on conditions. I’ll admit it: they look cool at night, but I wouldn’t trade the B58’s new growl for them.
So, is the 2025-updated M340i the sweet spot of the BMW lineup in 2026? I’d argue yes—and not just because of the extra lawnmower’s worth of power. It’s the fact that you can hustle this thing through a canyon, then immediately switch to Comfort mode and achieve Prius-like fuel numbers (okay, maybe not Prius-like, but close enough to make you feel virtuous). The M3 might have the track cred, but the M340i xDrive is the one you’ll actually live with every day. And with the M440i and M240i finally catching up, the B58 clan has never been stronger. If you haven’t driven one since the update, go find a dealership and remedy that. Just be prepared to be spoiled forever.
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