The B58 is BMW’s 3.0-litre turbocharged inline-six, and since 2016 it has been fitted
to twelve different model lines sold in the United States — from a 3,463 lb roadster to a
5,417 lb seven-seat SUV. This page is about that spread: what the same engine is asked to
do in each car, how its rated output has moved in five steps, and which of the twelve is
the one worth buying.
For the engine on its own — what it replaced, how it relates to the S58, why the Supra
has one — see our reference page on the BMW B58. What follows
is the application guide, built from the 173 US-certified versions in our
specification records that carry this engine.
Five outputs, and how to tell which one you are looking at
The B58 has never been sold at one power figure. EPA certification records give five
distinct ratings across its US life, and they map onto badges rather than onto years:
| Rated output | US model years | Badges that carry it |
|---|---|---|
| 320 hp | 2016–2018 | 340i |
| 335 hp | 2017–2026 | 540i, 740i, 840i, sDrive40i, xDrive40i |
| 355 hp | 2016–2019 | M40i (X3, X4) |
| 375 hp | 2023–2026 | 540i, 740i, M340i, M440i, M50i, sDrive40i, xDrive40i |
| 382 hp | 2020–2026 | M240i, M340i, M440i, M40i |
The rule that falls out of it is simple and worth carrying to a forecourt.
A 40i badge is the 335 hp or 375 hp engine; an M-something-i badge is the 355 hp or
382 hp engine. The plain 340i of 2016–2018 is the outlier: it is the lowest
output the B58 has ever been sold at in America, and it is also the first.
Sixty-two horsepower separates the bottom of that table from the top, inside one
engine family at one displacement. A listing that says “3.0-litre TwinPower Turbo six”
therefore tells you almost nothing about how quick the car is; the badge and the model
year do.
What BMW said when it launched
The archive holds the US brochure from the B58’s first American model year. The
2016 3 Series brochure introduces it in one
sentence, under a heading about power and efficiency: “An all-new 3.0-liter inline
six-cylinder engine in the 340i pours on 320 hp with 330 lb-ft of torque.”
Two things in that sentence are worth noticing a decade later. “All-new” is BMW
distinguishing it from the N55 it replaced, which shared the displacement and the layout
but not the architecture. And 320 hp with 330 lb-ft · 447 Nm is the figure the engine
started at — the same brochure lists the 328i’s four-cylinder at 240 hp and 255 lb-ft, and
a diesel at 180 hp and 280 lb-ft, so the six was the top of the ordinary 3 Series range
by 80 hp.
The twelve cars, and what the engine has to move
This is where the application guide earns its keep. The same engine, in twelve
different bodies, with the weight and the fuel economy that follow from them:
| Model | US model years | Badge | Output | Curb weight | EPA combined |
|---|---|---|---|---|---|
| Z4 | 2020–2026 | M40i | 382 hp | 3,463 lb | 22–26 mpg |
| 3 Series | 2016–2026 | 340i, M340i | 320–382 hp | 3,545–3,825 lb | 23–29 mpg |
| 5 Series | 2017–2026 | 540i | 335–375 hp | 3,682–4,019 lb | 23–28 mpg |
| 2 Series | 2022–2026 | M240i | 382 hp | 3,891–3,933 lb | 26 mpg |
| 4 Series | 2021–2026 | M440i | 375–382 hp | 3,977–4,189 lb | 25–30 mpg |
| X3 | 2018–2025 | M40i, M50i | 355–382 hp | 4,228 lb | 23–27 mpg |
| X4 | 2016–2024 | M40i | 355 hp | 4,235–4,323 lb | 21–23 mpg |
| 7 Series | 2020–2026 | 740i | 335–375 hp | 4,720 lb | 23–28 mpg |
| X5 | 2019–2026 | sDrive40i, xDrive40i | 335–375 hp | 4,707–5,302 lb | 22–25 mpg |
| X6 | 2020–2026 | sDrive40i, xDrive40i | 335–375 hp | 4,795 lb | 22–24 mpg |
| X7 | 2019–2026 | xDrive40i | 335–375 hp | 5,280–5,417 lb | 21–23 mpg |
| 8 Series | 2020–2026 | 840i | 335 hp | — | 23–25 mpg |
The weight column spans 1,954 lb · 886 kg from top to bottom. A Z4 M40i and an X7
xDrive40i share an engine family and are separated by most of a ton — and the X7 is the
one with the lower output, because the 40i badge sits below the M40i badge.
That is the least intuitive fact about the B58 range: BMW gives the biggest, heaviest cars
the softer tune.
Which one to buy
Read the table for the ratio rather than the headline and three cars separate
themselves.
The Z4 M40i is the extreme. 382 hp in 3,463 lb is the lightest car the
B58 has ever been put in for the US market, and it is the highest output. Nothing else in
the range is close: the next lightest is the 3 Series at 3,545 lb, and that one starts at
320 hp.
The M240i is the value case. 382 hp, 3,891 lb, and 26 mpg combined
— the same output as the Z4, in a car that is 428 lb heavier but returns better economy
than most of the range. Its EPA figure is bettered only by the M440i and the 3 Series at
the top of their spans.
The X7 xDrive40i is the one to check carefully. 5,280–5,417 lb on
335 to 375 hp and 21–23 mpg makes it the hardest-worked B58 in the range. It is not
a criticism of the engine so much as an observation about what you are asking of a
3.0-litre six: the X7 weighs 56% more than the Z4 with less power.
Across all 173 versions the median EPA combined figure is 25 mpg and the range is
21 to 30. For a 3.0-litre turbocharged six that spends half its life in SUVs, that
is a narrow band — the engine’s economy is remarkably insensitive to what it is bolted
into, which is not true of its acceleration.
What the six buys over the four
In most of the cars listed above the B58 is the upgrade from BMW’s 2.0-litre
four-cylinder, the B48. Because both are certified in the same
model years and the same models, the trade can be measured rather than argued about. Our
records hold 35 pairs where the same model in the same year was sold with both:
| What changes | Median difference | Range |
|---|---|---|
| Rated output | +120 hp | +72 to +157 hp |
| Curb weight | +167 lb · 76 kg | — |
| EPA combined | −2 mpg | — |
A 120 hp median uplift for two combined mpg and 167 lb is an unusually favourable
trade, and it has become more favourable over time. In 2017 the 3 Series six gave 72 hp
over its four; by 2020 the M340i gave 127 hp over the 330i, and the X3 M40i 134 hp over
the X3 30i. The four-cylinder did not get worse — the six-cylinder tune moved
up.
The two-mpg penalty is the number most likely to surprise. Two extra cylinders and
half again the displacement cost, on the EPA combined cycle, about as much as choosing
all-wheel drive does. That is not an argument that the six is efficient; it is an
observation that the combined cycle rewards a large engine running lightly loaded, which
is exactly the condition a 3.0-litre six is in for most of the test.
How the outputs moved
The five ratings are not five engines. They are one engine family through three
recognisable phases, and the dates in our records line up cleanly.
2016–2019: the introduction. 320 hp in the 340i, 355 hp in the
X3 and X4 M40i. The M40i models are the first sign that BMW intended to use this engine as
a performance unit rather than only as the six-cylinder option.
2020–2022: the step to 382. The M240i, M340i, M440i and the Z4
and X3 M40i all arrive at 382 hp. This is the phase where the “M Performance” tune becomes
the B58’s headline figure, and where the gap to the plain 40i cars opens to 47 hp.
2023–2026: 375 becomes the standard. The 540i, 740i, X5 and X7
move from 335 to 375 hp, closing most of the gap to the M cars. By this point a 740i has
more power than a 2016 X4 M40i did.
Anyone comparing a used 540i against a newer one should note that step specifically:
2017–2022 cars are the 335 hp version and 2023 onwards the 375 hp version, and the
badge does not change.
Checking which one a particular car has
Three steps, none of which require opening the bonnet.
Establish the model year and model from the VIN — our
VIN decoder returns both, and the method is set out in
how to decode a BMW VIN.
Look up that year and trim on our specification
pages. The horsepower shown there is from the EPA certification record for that
version, not from a press release, and the engine family is named where the certification
data supplies it.
Do not rely on the badge alone. A 540i is 335 hp or 375 hp depending
on year; a 40i is 335 or 375; an M40i is 355 or 382. In every case the model year is what
resolves it.
What is missing from the table, and why
Two columns you would expect in a guide like this are not there: torque and 0–60.
Neither is an oversight.
Torque and acceleration are not collected by any US government source. EPA certification
records horsepower and fuel economy; Transport Canada records dimensions and curb weight.
Torque figures exist in our records only where a factory brochure printed them in a
specification table — and our brochure archive thins out sharply after 2019, which is
exactly the period covering most of the B58’s life. Of the 173 B58 versions on file, none
carries a torque figure from a source we can name, so the column stays empty rather than
being filled from a press release someone else has already re-typed twice.
The one torque figure on this page — 330 lb-ft · 447 Nm for the 2016 340i —
is here because BMW printed it in the brochure we hold, and the page links to that
brochure so you can read the sentence yourself. That is the standard the rest of the table
would have to meet.
The 8 Series row has no curb weight for the same kind of reason: Transport Canada does
not publish one for that model, so the cell is a dash. A dash on this site means “not
published by a source we can cite”, never “roughly the same as the row above”.
What we do not publish about it
You will not find a reliability score or a complaint count for the B58 here, on this
page or on the engine page, and the reason is structural rather
than editorial caution. NHTSA records complaints against a vehicle. A 2019
3 Series in that database may have a B48 four-cylinder or a B58 six, and the complaints
for both sit in one bucket with no field that separates them. Any figure presented as
“complaints about the B58” has been produced by guessing which ones belong to it.
What is on the record and is worth knowing: the B58 has been in continuous US
production since the 2016 model year across twelve model lines, which makes it one of the
longest-running single engine families in BMW’s modern range. That is a fact about
production, not about durability, and we are not going to dress it up as the second
thing.
Common questions
How many BMW models have the B58?
Twelve model lines in the United States: the 2, 3, 4, 5, 7 and 8 Series, the Z4, and
the X3, X4, X5, X6 and X7. Our records hold 173 individual US-certified versions carrying
this engine.
Which BMW has the most powerful B58?
The 382 hp version, fitted to the M240i, M340i, M440i and the Z4 M40i and X3 M40i. In
the Z4 that output moves the lightest car in the range at 3,463 lb.
Is the 540i B58 the same as the M340i B58?
Same engine family, different tune. Through 2022 the 540i was rated at 335 hp against
the M340i’s 382; from 2023 the 540i moves to 375 hp.
What fuel economy does the B58 return?
21 to 30 mpg combined depending on the car, with a median of 25 across all 173
US-certified versions. The M440i and 3 Series reach 29–30; the X7 and X4 sit at
21–23.
Did the B58 replace the N55?
Yes. The 2016 3 Series brochure calls it “an all-new 3.0-liter inline six-cylinder
engine”, introduced in the 340i at 320 hp. The N55 was the
outgoing single-turbo six.
Is a B58 in an X7 the same engine as in a Z4?
The same family, differently rated and doing a very different job: 335–375 hp in a
5,280–5,417 lb X7 against 382 hp in a 3,463 lb Z4.
Sources
- Outputs, model years, curb weights and fuel economy from this site’s specification pages, compiled from EPA fuel-economy filings, EPA certification test records and Transport Canada vehicle specifications. 173 US-certified versions carry this engine family.
- The 2016 BMW 3 Series US brochure held in this site’s archive, source of the launch description and the 320 hp / 330 lb-ft figures.
- EPA fueleconomy.gov: the underlying record of every version certified for US sale.