BMW S55B30 engine code explained
S55B30 is the full code for the M Division's twin-turbo straight-six in the F80 M3, F82 / F83 M4 and F87 M2 Competition and M2 CS. It is loosely based on the N55 but with a closed-deck block, forged crank, two mono-scroll turbos and a crank-hub design that became the engine's most argued-about feature. Two output codes covered every car; the M3 / M4 unit is the T0, the M2 Competition the O0.
Quick answer
The S55B30 is the 3.0-litre straight-six twin-turbo M engine petrol of the BMW S55 family, built 2014-2021. Bimmer.AI scores the family 7 / 10: a strong used buy with a short list of known preventatives. The tables below give every output tier and sticker letter BMW used on this stem and which cars got them; the failure table is the same one that powers the S55 family guide.
How to read S55B30
| Part of the code | Meaning |
|---|---|
| S | BMW M GmbH (M Division) engine |
| 55 | engine family number within the S-series |
| B | petrol, longitudinal (rear-drive platform: 1 to 8 Series, X3 to X7, Z4) |
| 30 | displacement in tenths of a litre: 3.0 litres |
| K / U / M / O / T / S + digit | output tier and revision, appended in BMW's internal naming (for example S55B30O1) |
| A / B / C / D | parts-catalogue engine version printed on the engine cover sticker (for example S55B30A) |
S55B30 output tiers and which cars have them
| Code | Output | Cars | Notes |
|---|---|---|---|
| S55B30T0 | 425 bhp (M3 / M4), 444 bhp (Competition), 454 bhp (M3 CS / M4 CS), 493 bhp (M4 GTS) | M3 (F80 2014-2018), M4 (F82 / F83 2014-2020), M4 GTS (2016) | The M3 / M4 engine; water injection on the GTS |
| S55B30O0 | 404 bhp (M2 Competition), 444 bhp (M2 CS) | M2 Competition (F87 2018-2021), M2 CS (2020-2021) | Detuned M3 unit replacing the N55 in the M2 |
S55B30 sticker letters: S55B30A
The letter does not distinguish anything a buyer needs. The two conversations on every S55 are the rod bearings (the defining M preventative, £1,500 to £2,500 at 60,000 to 80,000 miles) and the crank hub, which can slip on tuned cars; a pinned or keyed hub is the standard fix on anything running more than a Stage 1 map. Then the plastic charge pipes and the usual oil-filter-housing gasket.
| Sticker code | What it denotes |
|---|---|
| S55B30A | Standard parts-catalogue version across M3, M4 and M2 Competition. |
Known problems on every S55B30
Failure data is held once, per engine family, so this table is identical to the BMW S55 guide. Cost ranges are indicative UK figures.
| Failure mode | Severity | Frequency | Typical onset | UK repair range |
|---|---|---|---|---|
| Rod bearing wear | Catastrophic | Common | 40 to 100k mi | £1,500 to £2,500 |
| OEM plastic charge pipe failure | Moderate | Very common | 20 to 80k mi | £150 to £400 |
| Valve cover gasket leak | Moderate | Common | 50 to 120k mi | £300 to £500 |
| Crank hub slip (heavily modified cars) | Catastrophic | Uncommon | 30 to 100k mi | £1,200 to £2,000 |
| Intake valve carbon buildup | Moderate | Common | 50 to 100k mi | £400 to £700 |
Long-term verdict
Reliable with preventative service. Rod-bearing replacement at 50,000 to 70,000 miles is the defining S55 preventative; BMW updated the rod-bearing specification mid-production. Charge pipe upgrade is standard practice (OEM plastic fails under boost). With those two items addressed and a clean service history, 200,000+ miles is realistic. Tracked cars carry higher wear; verify track-day evidence at viewing.
Check a specific S55B30 listing
Paste any BMW S55 listing, VIN or registration. Bimmer.AI identifies the exact engine and returns the buyer report in 30 seconds.
Run a Bimmer.AI buyer report →Bimmer.AI is designed to help you identify BMW-specific buyer risks before you travel, negotiate, or pay for an inspection. It does not replace a physical inspection by a qualified mechanic, a legal vehicle-history check (e.g. HPI Check), or independent verification of finance, stolen, or write-off status. Repair-cost ranges are indicative UK figures that vary by region, specialist, parts supply, and labour rates.
Frequently asked questions
S55B30 crank hub: how worried should I be?
On a stock car, not very: documented crank-hub slips on unmodified S55s are rare. On a tuned car, very: extra torque loads the friction-fit hub and a slip bends valves. If the listing has been mapped, insist on evidence of a pinned or keyed hub (£1,000 to £2,000 installed) or price the job in. Rod bearings are the more universal preventative on either.
Is the M2 Competition S55B30O0 the same as the M3 engine?
Same block, head, turbos and internals; the O0 is a software and cooling-package detune to 404 bhp (444 bhp in the M2 CS). It inherits the M3 / M4's rod-bearing and crank-hub conversations, so buy it with the same checks. The earlier F87 M2 (2016 to 2018) used the N55B30T0 instead, a different and simpler engine.
Which BMWs have the S55B30 engine?
The S55B30 went into the following cars, by output tier. S55B30T0 (425 bhp (M3 / M4), 444 bhp (Competition), 454 bhp (M3 CS / M4 CS), 493 bhp (M4 GTS)): M3 (F80 2014-2018), M4 (F82 / F83 2014-2020), M4 GTS (2016); S55B30O0 (404 bhp (M2 Competition), 444 bhp (M2 CS)): M2 Competition (F87 2018-2021), M2 CS (2020-2021). The two-letter family badge is S55; any listing that quotes the family code is talking about one of these.
Is the BMW S55B30 reliable?
Bimmer.AI scores the S55 family 7 out of 10, which makes the S55B30 a strong used buy with a short list of known preventatives. Reliable with preventative service. Rod-bearing replacement at 50,000 to 70,000 miles is the defining S55 preventative; BMW updated the rod-bearing specification mid-production. Charge pipe upgrade is standard practice (OEM plastic fails under boost). With those two items addressed and a clean service history, 200,000+ miles is realistic. Tracked cars carry higher wear; verify track-day evidence at viewing.
What does S55B30 mean?
S is the BMW M GmbH (M Division) engine, 55 is the family number, B means petrol, longitudinal (rear-drive platform: 1 to 8 Series, X3 to X7, Z4), and 30 is the displacement in tenths of a litre (3.0 litres). BMW appends an output tier and revision (K, U, M, O, T or S plus a digit) in its own naming, and the parts catalogue adds a version letter (A, B, C) that is what you see on the engine cover.