BMW Engine Codes Explained: How to Read Any BMW Engine Name

A BMW engine code like B58B30M0 looks like a random string, but every character means something — and once you can read it, you can decode any BMW or MINI engine at a glance: its family, how many cylinders it has, what fuel it burns, how it's mounted, its displacement, and even where it sits in BMW's output hierarchy. We work on these engines every day, so this is the plain-English key to the whole system, with the one or two details most explainers get wrong.

The short version: a modern BMW engine code is built from a family letter, a cylinder digit, a variation digit, a fuel-and-mounting letter, a two-digit displacement, and an optional performance-class letter and revision number. Read left to right, it is a compact spec sheet. Here is each piece.

The anatomy of a code

Take B58B30M0, the six in a 340i, and read it in order:

Most people only ever say the first three characters — "B58" — which is the engine family. The full code carries the rest. Now each field in detail.

1. The family letter — who built it and when

The first letter tells you the engine's lineage:

This single letter is the most useful one. N is the generation that includes the N20, N52, N54, and N55. B is the modular family — B38, B48, B58 and their diesel siblings. S is BMW M's production engines for road cars: the S55 in the F8x M3/M4, the S58 in the current M3/M4/M2. P is reserved for pure motorsport engines that never powered a road car — the P48 that raced in DTM, the P58 in the M4 GT3. So an "S" engine is the M version you can buy; a "P" engine is the one that only races.

2. The cylinder digit — and the trap everyone falls into

The first number is a coded cylinder count, not a literal one. This is the field most casual explainers get wrong:

Read that table twice, because it is the thing to remember: a "5" means a straight-six, not a five-cylinder. The B58, N55, and S58 are all inline-sixes despite the 5 in the middle. A "6" is a V8 (the S63, N63), a "7" is a V12 (the N74), and an "8" is the V10 (the S85 of the E60 M5). BMW's numbering is consistent — it just is not the literal count.

3. The variation digit — which version of the concept

The second number marks how far the engine has moved from the original "0" design of that family. The numbers run in development order but do not necessarily supersede each other — an N54 and an N55 are different engines from the same era, not "version 4 then version 5" of one motor. In the modular B-series, this position also carries the fuel split: BMW used 8 for the petrol modular engines and 7 for the diesels, which is why the petrol four is a B48 and the diesel four a B47.

4. The fuel-and-mounting letter — the detail that explains MINIs

After the family/cylinder/variation block comes a letter that tells you both the fuel and how the engine sits in the car:

This is why the same 2.0-liter four can read B48B20 in a rear-drive 330i (longitudinal) and B48A20 in a MINI or a front-drive-based M235i (transverse) — same engine, different orientation, captured in one letter. If you have ever wondered how a MINI Cooper S and a 330i can share an engine, the code tells you: they run the same B48, mounted two different ways.

5. The displacement — the easy one

The two digits after the fuel letter are displacement in tenths of a liter: 30 = 3.0 L, 25 = 2.5 L, 20 = 2.0 L, 16 = 1.6 L. So B58B30 is a 3.0-liter, B48B20 is a 2.0-liter, and the little B38B15 is a 1.5-liter three-cylinder.

6. The performance class and revision — where an engine sits in the hierarchy

On the N and B families, the final letter is the performance class — BMW's own ranking of how hard a given engine is tuned from the factory:

And the last digit is the revision: 0 for the original development, 1 through 9 for each subsequent redesign. (On the older M family, a "TU" suffix — Technical Update — did the same job before BMW switched to the numbered system.)

This field is how you place an engine within its own family. Take the B48 four: in a base 320i it sits low in the order, in a 330i it's an upper-class "O," and in the 302-horsepower M135i, X2 M35i, and MINI JCW GP it becomes B48A20T1 — the "T," top performance class, transverse-mounted, first revision. Same B48 block, but the code tells you that the JCW GP engine is the factory's top-tier tune of it. We walk through that exact engine, from the road to the race track, in our B48-to-P48 feature.

Decoding real engines

Put it together and any BMW engine reads cleanly:

• N55B30 — N-generation, inline-six (the 5), 3.0 liters. The single-turbo six in the 335i and the first M2. (N55 guide)
• B58B30 — modular, inline-six, 3.0 liters. The 340i, M340i, and Supra six. (B58 guide)
• S58B30 — M production engine, inline-six, 3.0 liters. The current M3/M4/M2 engine. (S58 guide)
• B48A20T1 — modular, inline-four, petrol, transverse, 2.0 liters, top performance class. The 302-hp JCW GP and X2 M35i engine. (B48 guide)
• P58 — Motorsport racing engine, inline-six. The M4 GT3's ~590-hp race six. (B58 vs S58 vs P58)

One more wrinkle: the SULEV twins

In California and other strict-emissions states, BMW sells emissions-specific versions of some engines under their own codes — the B46 is the SULEV version of the B48, and the N26 is the SULEV version of the N20. They are mechanically the same engines with different emissions hardware, so if a parts catalog or a VIN shows a B46 where you expected a B48, that is why. It is the same engine wearing a different emissions suit.

(Engine codes are a separate system from BMW's chassis codes — the F30, G80, or E46 that name the car rather than the motor. Those follow their own logic, and they are worth their own guide.)

Why this matters

Reading the code is not trivia — it is practical. It tells you, instantly, whether two cars share an engine (and therefore parts and tuning), what generation you are dealing with when you buy used, and where your engine sits in BMW's own output hierarchy. When you know your car is a B48A20T1, you know it is the transverse, top-tier version of the modular four — which is exactly the kind of thing that decides what parts fit and how far it tunes. When you're ready to act on that, you can build your tune for your exact engine. [LP: a one-line shop note — e.g., the codes you most often have to correct customers on, or the decode that saves the most parts-ordering mistakes.]

Frequently asked questions

What do BMW engine codes mean? Each character is a spec: the first letter is the engine family (M, N, B, S, P), the first number is a coded cylinder count, the next number is the variation, a letter gives fuel and mounting, two digits give displacement in tenths of a liter, and an optional letter and number give the performance class and revision. So B58B30M0 is a modular inline-six, 3.0 liters, petrol, middle performance class.

Why is a B58 a six-cylinder if it has a "5" in it? Because BMW's cylinder digit is coded, not literal: 3 = inline-3, 4 = inline-4, 5 = inline-6, 6 = V8, 7 = V12, 8 = V10. The 5 in B58, N55, and S58 all mean a straight-six.

What is the difference between an S and a P engine? An S engine is a BMW M production engine that powers road cars — the S55, S58, S63. A P engine is a BMW M Motorsport racing engine that never powered a road car — the P48 (DTM) and P58 (M4 GT3).

What does the letter after the displacement mean (the A or B)? It gives fuel type and mounting: A is petrol transverse, B is petrol longitudinal, C and D are diesel, E is electric. It is why a B48B20 in a 330i and a B48A20 in a MINI are the same engine mounted differently.

Where does the high-output B48 fit? It is B48A20T1 — the "T" is the top performance class, "A" is transverse-mounted, "20" is 2.0 liters. That is the 302-horsepower version in the M135i, X2 M35i, and MINI JCW GP.

What is a B46 or an N26? They are the SULEV (strict-emissions) versions of the B48 and N20 — the same engines with emissions-specific hardware, sold in California and similar markets.