BMW engine codes explained: how to read S85, N55 and B58

BMW engine codes such as S85B50, N55B30 or B58B30 can look like random letters and numbers. In fact they follow a logical system that tells you who developed the engine, how many cylinders it has, what fuel it uses and its displacement.

In this guide we explain how to read modern BMW engine codes, what each position means, the difference between M, N, B and S engines, and the most important BMW engines with their codes.

Why BMW engine codes matter

Model names like 335i or M5 tell you little about the engine under the bonnet. Over the years, the same model name has been used with very different engines. A 335i from 2007 has a different engine than a 335i from 2011, and an M5 can have a six-cylinder, a V8 or a V10, depending on the generation.

The engine code is much more precise. It tells mechanics, parts suppliers and enthusiasts exactly which engine is fitted. This matters when you order parts, read about common problems, look for tuning information or check if a car is original.

Enthusiasts often talk about engines by their codes: the S54 of the E46 M3, the N54 of the 335i, the B58 of the modern M340i. Knowing how the codes work helps you understand these conversations and make better decisions when buying or maintaining a BMW.

The system described here applies mainly to BMW engines from the 1990s onwards. Older engines used a simpler scheme.

The first letter: who developed the engine

The first letter shows the engine family or the developer:

• M was used for BMW engines developed until the early 2000s, for example the M50, M52 and M54 straight-sixes and the M62 V8.
• N stands for the new generation of BMW engines from the 2000s, such as the N52, N54, N55 and N63.
• B is used for the modular engine family introduced in the 2010s, such as the B38 three-cylinder, the B48 four-cylinder and the B58 six-cylinder.
• S marks engines developed by BMW M for the M cars, such as the S54, S62, S65, S85, S55, S58 and S68.
• P is used for pure racing engines from BMW Motorsport.
• W was used for engines bought from other manufacturers.

So when you see an engine code that starts with S, you know immediately that it is a BMW M engine.

The second digit: the number of cylinders

The second character, a digit, shows the cylinder layout. The system is not completely uniform across all generations, but in modern BMW engines it usually works like this:

• 3 = three cylinders (for example B38)
• 4 = four cylinders (for example N47, B48)
• 5 = six cylinders in line (for example N52, N55, B58, S55, S58)
• 6 = V8 (for example N63, S63, S65, S68)
• 7 = V12 (for example N74)
• 8 = V10 (for example S85)

Some older and smaller engines use other digits, but for the most important modern engines this rule works well. When you see S85, you can read it as: BMW M engine, V10.

The third digit, the fuel and the displacement

The third character shows a change in the basic design of the engine. A higher number usually means a newer or significantly modified version. For example, the N54 and N55 are both turbocharged straight-sixes, but the N55 is a different, newer design with one twin-scroll turbocharger instead of two turbochargers.

After the first three characters comes a letter that shows the fuel type and the installation: B for petrol (Benzin in German) and D for diesel.

The next two digits show the displacement in decilitres: 30 means 3.0 litres, 44 means 4.4 litres and 50 means 5.0 litres.

So S85B50 reads as: BMW M engine (S), V10 (8), basic design 5, petrol (B), 5.0 litres (50). And B58B30 reads as: modular engine family (B), straight-six (5), design 8, petrol (B), 3.0 litres (30).

Suffixes and power levels

Many engine codes have additional letters and numbers at the end. They show technical updates or different power levels of the same basic engine.

TU stands for technical update, for example the M52TU, which received double VANOS and other improvements.

In newer codes, a short suffix can show the power level and the version of the engine. The same B58B30 engine, for example, exists in several versions with different outputs for different models, and the suffix helps to tell them apart.

When you order parts, the full engine code with its suffix, together with the vehicle identification number (VIN), is the safest way to get the correct part. Parts can differ between versions even when the main code is the same.

Important BMW engines by code

These are some of the best-known BMW engines and the cars they power:

• M30 – the "big six" of the 1970s and 1980s, in many 5, 6 and 7 Series models.
• S14 – the four-cylinder of the E30 M3.
• S38 – the straight-six of the E28 and E34 M5.
• S54 – the 343 hp straight-six of the E46 M3.
• S62 – the 400 hp V8 of the E39 M5.
• S85 – the 507 hp V10 of the E60 M5 and M6.
• S65 – the 420 hp V8 of the E9x M3.
• N54 – the first twin-turbo straight-six, in the 335i and other models.
• N55 – its successor with one twin-scroll turbocharger.
• S55 – the twin-turbo six of the F80 M3, F82 M4 and M2 Competition.
• B58 – the modern straight-six of many current BMWs.
• S58 – the twin-turbo six of the G80 M3, G82 M4 and current M2.

Knowing these codes is a great start for understanding BMW's engine history.

Examples of BMW engine codes

Item	Details
S85B50	BMW M · V10 · petrol · 5.0 l (M5 E60)
S54B32	BMW M · straight-six · petrol · 3.2 l (M3 E46)
S62B50	BMW M · V8 · petrol · 4.9 l (M5 E39)
N55B30	New generation · straight-six · petrol · 3.0 l
B58B30	Modular family · straight-six · petrol · 3.0 l
S58B30	BMW M · straight-six · petrol · 3.0 l (M3/M4 G8x)
N47D20	New generation · four-cylinder · diesel · 2.0 l

Frequently asked questions

What does the S mean in BMW engine codes?

An engine code starting with S shows an engine developed by BMW M for the M cars, such as the S54, S65, S85 or S58.

How do I read the BMW engine code S85B50?

S = BMW M engine, 8 = V10, 5 = basic design, B = petrol, 50 = 5.0 litres. It is the V10 of the M5 E60 and M6.

What is the difference between N and B engines?

N engines belong to the BMW engine generation of the 2000s, such as the N54 and N55. B engines belong to the newer modular family from the 2010s, such as the B48 and B58.

Where can I find the engine code of my BMW?

The engine code is stamped on the engine block and listed in the vehicle documents. A dealer or a VIN decoder can also show it.

Sources

• BMW Group – BMW engine technology
• BMW Group Classic – engine history
• BMW Group PressClub – technical data of BMW engines