The BMW B48 is a turbocharged 4-cylinder engine that started production in 2014 as a replacement for the BMW N20. The B48 features an aluminum block and head design, a new under-square configuration, a stronger crankshaft, upgraded pistons, and improved bearings over its predecessor.
The B58 straight-6 turbo on the other hand started production in 2015, and it replaced the BMW N55 engine. The B58 increased boost pressure by 20% over its predecessor, it also features a new closed-deck design with stronger internals.
Both of these powerplants feature a single twin-scroll turbocharger, direct injection, VANOS, Valvetronic, and a water-to-air intercooler. The high amount of shared components and similar design is no surprise as they are part of BMW’s new modular engine family.
Now it’s time to put these two modern BMW powertrains in a head-to-head matchup.
BMW B48 vs. BMW B58 Specifications
| BMW B48 (B48A20O1) | BMW B58 (B58B30O1) | |
|---|---|---|
| Horsepower | 255 hp @ 5000 – 6,500 rpm | 382 hp @ 5,000 – 6,500 rpm |
| Torque | 295 lb⋅ft @ 1,550 – 4,400 rpm | 369 lb⋅ft @ 1,600 – 4,500 rpm |
| Displacement | 2.0L (1,998 cc) | 3.0 L (2,998 cc) |
| Engine configuration | Inline-4 | Inline-6 |
| Turbo | Single twin-scroll turbocharger | Single twin-scroll turbocharger |
| Bore & stroke | 82.0 mm x 94.6 mm | 82.0 mm x 94.6 mm |
| Compression ratio | 8.9:1 | 11:1 |
| Redline | 7,000 RPM | 7,000 RPM |
| Cooling | Water-to-air intercooler | Water-to-air intercooler |
B48 vs. B58: Horsepower & Torque
The B48 (B48A20O1) makes 255 hp and 295 lb⋅ft while the B58 (B58B30O1) outputs 382 hp and 369 lb⋅ft. Both engines output maximum horsepower between 5,000 and 6,500 RPM. Maximum torque is achieved between 1,550 and 4,400 RPM in the B48, and between 1,600 and 4,500 RPM in the B58. It is clear that the B58 produces considerably more power, to the surprise of no one.
The B58 in a M340i produces nearly 50% more horsepower and 25% more torque than the B48 in a 330i
Torque curves are similar, but we can see that the B58 is much stronger at the top end of the RPM range, where the B48 starts losing steam. The B48 is indeed more impressive in the lower end of the rev range, as it produces close to 300 lb⋅ft from 1,600 rpm all the way to 4,500 rpm.
The B58 will feel a lot stronger on the higher end. Those two extra cylinders and the extra liter of displacement become very apparent above 4,000 RPM.
B48 vs. B58: Power delivery
The B58 delivers more power throughout the entire RPM range. The B48 has considerable amounts of torque that is more than sufficient for city, highway driving, and spirited driving. But it will never blow your pants off or caught you off guard like the B58 can.
Despite their turbocharged nature, both engines have a relatively linear power curve. BMW has done an increadible job at minimizing turbo lag. Power delivery in both is fairly linear compared to most turbocharged engines.
Both engines delivery power with little turbolag; the B58 is stronger throughout the rev range
However, the B48 is a smaller engine, and turbo lag is slighly more noticeable. This is usually the case with 4-cylinder 2.0L engines as they rely on turbochargers a lot more than a comparably larger engine such as the 3.0L B58 which is rarely caught off-guard.
It is important to note that the B58 is much smoother and will transmit less vibrations to the cabin than the B48. An inline-6 is inherently balanced while inline-4 engines are not.
B48 vs. B58: Tuning & mods
The BMW B58 is often called the modern 2JZ, an engine widely regarded as one of the most tunable engines out there. The B58 has been a tuner’s delight ever since it came out: a couple of mods and a tune can increase power significantly. Highly modified examples can reach 1,000 horsepower.
The tuning community is also bigger for the B58, with a large number of aftermarket modifications and ECU tunes available. You’ll find lots of information if you decide to modify your car to extract the most power possible out of the B58.
Both engines respond well to mods, but the B58 has a higher power ceiling
Nonetheless, the B48 is an impressive turbo inline-4. It puts into shame some engines with much higher displacement even on stock form. Similarly, it responds very well to mods and ECU tunes, but the power ceiling is lower. A highly modified B48 will be barely more powerful than the B58.
Both engines respond well to a catless downpipe, and an ECU tune. Turbo upgrades are possible for both. Other notable mods for the B48 and the B58 include aftermarket intakes and port injection.
B48 vs. B58: Sound
“There is no replacement for displacement.” The B58 is a better-sounding engine, period. BMW has perfected the sound coming out of their inline-6 engines, and the B58 is yet another engine that outputs a refined groan at low-RPMs and aggressive roar at high-RPMs.
The 4-cylinder B48 engine sounds much more ordinary, not much different than any of the other countless 4-cylinders out there. Although its turbocharged nature gives it a bit more grunt, the exhaust note doesn’t compare to that of an inline-6 or a V8. BMW tries to remedy that by pumping fake engine noise into the cabin.
The B58 sounds much better than the B48
The B48 does not sound too promising even for a 4-cylinder engine; many have compared it to the sound of a diesel engine. It does not let alone comparing it to a 3.0L straight-six.
If you snap on a well-made aftermarket exhaust on the B58, you’ll soon realize that it sounds better than some 8-cylinder engines. Whether it be the connection to the 2JZ as the B58 does share an audible identity with the 2JZ or it is simply due to the fact that the B58 sounds similar to modern-day 6-cylinder racing cars.
B48 vs. B58: Fuel Efficiency
The BMW 330i with the B48 is EPA-rated for a combined city/highway fuel economy of 30 MPG, while the M340i with the B58 is rated for an average of 25 MPG. Both are relatively high numbers if we take into account the ludicrous amount of power these two engines produce. Fuelly numbers tell us a different story, however. A 2020 330i with the B48 averages 27.5 MPG, while a 2020 M340i with the B58 averages 22.8 MPG.
The B48 is a more efficient engine with impressive fuel economy
A BMW M340i with the B58 can achieve around 32 MPG on the highway. This is excellent fuel economy for a car with almost 400 hp on tap. On the other hand, the 330i with the B48 averages closer to 40 miles per gallon on the highway.
The B58 consuming more fuel is expected, as it has two extra cylinders. But it is impressively efficient for a 3.0L engine considering the horsepower and torque figures it can output.
B48 vs. B58: Reliability & Common Issues
The past 7-8 years have shown that both engines have proved to be reliable. The B58 does have a slight edge as long-term data has shown that BMW 6-cylinder engines fare better compared to 4-cylinder engines.
Both engines are also more reliable than their predecessors and are the most reliable turbocharged BMW engines to date. Only time will tell if they will be as reliable as the naturally-aspirated inline-6s BMW used to make.
Based on previous BMW engines, the B58 will most likely have fewer issues than the B48
Nonetheless, no engine is perfect, and these do have some common issues. Coolant loss is a common problem, and VANOS actuators might need to be replaced eventually. Oil leaks may start to appear at very high mileage as well, but it’s not as big of an issue as it was in older BMWs.
Early B48 models also have an issue with oil leaking from the turbo oil line, and an issue not present on the B58.
Closing thoughts
The B48 and the B58 are the latest iterations of turbocharged 4 and 6 cylinder engines from BMW. Both are considerably better than its predecessors and have proven that BMW continues to improve the internal combustion engine.
Which one is better for you? Depends what you want out of your car. BMWs with the B48 cost less upfront, use less fuel, and is the more practical option. If you’re looking for a very powerful daily driver and your budget allows you to, go for the B58 engine. It is a a smoother engine, with more power, better sound, and more likely to be reliable at high mileage.