BMW S55 engine explained: the twin-turbo six of the F80 M3 and F82 M4
The BMW S55 brought turbocharging to the M3 and M4. How the twin-turbo straight-six is built, the versions from the M2 Competition to the M4 GTS, known issues and the maintenance it needs.
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The BMW S55 is the engine that brought turbocharging to the M3. This 3.0-litre twin-turbo straight-six powered the F80 M3, F82 and F83 M4, and later the M2 Competition and M2 CS, from 2014 to 2021.
It replaced the naturally aspirated V8 of the E92 M3 with far more torque and better efficiency, while keeping a free-revving character. In this article we explain how the S55 is built, its versions, known issues and the maintenance that keeps it healthy.
From V8 to twin-turbo six
The fourth-generation M3 used the S65 V8. For the F80 generation, BMW M returned to a straight-six, but with two turbochargers. Our article on the BMW S65 engine explains the V8 it replaced.
The change was driven by efficiency rules and the desire for more torque. The S55 delivered much more torque from low revs than the S65, while using less fuel in normal driving.
How the BMW S55 is built
Key features of the BMW S55 include:
- A 3.0-litre straight-six with a closed-deck crankcase for strength.
- A forged crankshaft and lightweight internal parts.
- Two mono-scroll turbochargers, each feeding three cylinders.
- Direct fuel injection and Valvetronic variable valve lift.
- Double VANOS for variable camshaft timing. Our article on BMW VANOS explains how it works.
- An extensive cooling system with several radiators for track use.
The engine is related to the N55 used in regular BMWs, but most important parts were changed by BMW M. Our article on BMW engine codes explains the names.
Versions and power outputs
The S55 was used in several models with different outputs:
- F80 M3 and F82/F83 M4: around 431 hp, and around 450 hp with the Competition package.
- M3 CS and M4 CS: around 460 hp.
- M4 GTS: around 500 hp, with a water injection system to cool the intake air.
- M2 Competition: a slightly detuned version with around 410 hp.
- M2 CS: around 450 hp.
Exact outputs vary by market. Our F80 M3 buying guide and our comparison of the M2 F87 and G87 explain these cars.
Known issues
The S55 is generally strong, but owners should be aware of:
- Crank hub: the connection between the crankshaft and its drive gear is widely discussed. Failures are rare on standard cars, but the risk is higher on heavily tuned engines. Some owners fit an upgraded hub.
- Charge pipe: the original plastic pipe can crack, especially with higher boost. Our article on BMW turbo problems explains boost leaks.
- Oil leaks: check the oil filter housing and oil pan.
- Spark plugs and coils: turbo engines are sensitive to worn plugs, especially when tuned.
- Carbon build-up: direct-injection engines can develop deposits on intake valves. Our article on BMW carbon build-up explains this.
Regular maintenance prevents most problems.
Maintenance that matters
To keep a BMW S55 healthy:
- Use the correct approved oil and change it more often than the maximum interval if the car is driven hard. Our article on BMW M engine oil explains the requirements.
- Warm up the engine before using full boost and let it cool after hard driving.
- Replace spark plugs at the recommended intervals, or earlier on tuned cars. Our article on BMW spark plugs and ignition coils explains why.
- Check the cooling system and fix leaks quickly.
- Keep records of all work.
A documented S55 with regular maintenance is a strong and reliable engine.
Tuning the S55
The S55 responds very strongly to software tuning, and many cars have been modified. Before buying or tuning:
- Consider the crank hub, charge pipe and cooling upgrades often fitted with higher power.
- Check the gearbox and clutch, which must cope with the extra torque.
- Make sure modifications are legal and declared to your insurer.
- Remember the effect on warranty and resale value.
A standard car with full history is usually the safest long-term choice.
Sound and character
The S55 has a different character from the S54 and S65. It delivers its torque early and pulls hard through the mid-range, while still revving freely. Its sound is more mechanical and turbo-influenced than the naturally aspirated engines, and many cars use enhanced sound in the cabin. Our article on BMW Active Sound Design explains this.
Some enthusiasts prefer the older naturally aspirated engines, but few argue with the S55's performance.
The successor: S58
The S55 was replaced by the S58 in the G80 M3, G82 M4 and later M2. The S58 offers more power, better cooling and more potential for high outputs. Our article on the BMW S58 engine explains the differences.
The S55 remains an important engine in M history: the first turbocharged M3 engine and the heart of a generation of fast, affordable used M cars.
BMW S55 engine at a glance
| Item | Details |
|---|---|
| Layout | 3.0-litre straight-six, twin mono-scroll turbos |
| Crankcase | Closed-deck |
| Power | From around 410 hp (M2 Competition) to 500 hp (M4 GTS) |
| Models | F80 M3, F82/F83 M4, M2 Competition, M2 CS |
| Known checks | Crank hub on tuned cars, charge pipe, leaks |
| Special feature | Water injection on the M4 GTS |
| Successor | S58 |
Frequently asked questions
Which cars have the BMW S55 engine?
The F80 M3, F82 and F83 M4, including CS and GTS versions, and the M2 Competition and M2 CS.
Is the BMW S55 reliable?
Yes, when maintained. Most issues are linked to heavy tuning, the charge pipe and normal turbo engine maintenance.
What is the S55 crank hub issue?
A discussed weakness in the connection between the crankshaft and its drive gear, mainly a risk on heavily tuned engines.
How much power does the S55 make?
From around 410 hp in the M2 Competition to around 500 hp in the M4 GTS.
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