BMW S55 Six Cylinder Turbocharged Engines

BMW S55 engine

An S55, note the large air / water intercooler.


The S55 is a three litre turbocharged engine derived from the N55 used in the 335i. It's far more highly tuned and makes around 30% more torque. BMW did a lot more than just bolt on a second turbo to the N55, there is a lot of improved engineering in this engine which isn't obvious at first inspection.

It was introduced in 2014 and powers the current F80 M3 and the F82 M4. It replaced the four litre S65 V8 used in the previous E90 M3.

BMW S55 engine

Cutaway of S55 taken from the rear.


Much of the S55 is similar to the N55, after all the N55 is a pretty high performance lump even in non-M form. Displacement is unchanged but the crankshaft is now forged and pistons are a new Mahle design with a low friction coating to help it rev to 7600rpm.

A big change is that bore and stroke are now 89.6x80 vs 84x89.6 on the N55. This shorter stroke will reduce piston velocity. That's a good thing because is reduces engine wear at high rpm and makes the engine easier to rev.

It uses a magnesium sump to save weight, so watch out on those speed bumps! The sump is baffled to help oiling under hard cornering. This should be retrofitted to the N55.

It still has direct injection, double VANOS and uses the Valvetronic system in place of a normal throttle plate, albeit a version with faster reaction times. Thankfully it now has an oil cooler but not an oil catch can. In my opinion an after market catch cans is a must if you don't want this engine to gunk up.

When you open the bonnet the first thing that catches the eye is a large water / air intercooler. Not only is this easier to package than a traditional air / air intercooler but it's less likely to be damaged by road debris and BMW claim it's more efficient.

The N54 had twin turbos, the N55 had a single twin scroll turbo and now the S55 had gone back to twin Mitsubishi units. Each operates with three cylinders and they run around 19psi of boost. They have electronically controlled wastegates, the N55 used pneumatic operation.

High pressure fuel pump reliability was a bit of the problem on the N54 and N55, well this engine has a pair of them so let's hope they're more reliable. They're plumbed in series and the second only turns on at times of high fuel demand above 3000rpm.

BMW claim the cooling system is "track ready", many owners will have their fingers crossed on that score as it could be a problem on the N54 and N55.

BMW S55 engine

Cylinder cutaway showing direct injection.


Code Size Power
Made Bore x
Timing Weight
VANOS Used in
S55 3.0 425 @ 5500-7300 410 @ 1850-5500 142 137 2014 on 89.6x80 Chain ? Double F80 M3
F82 M4


BMW S55 engine

Unusually the S55 has only one throttle body.


These engines generate a lot of heat and need a cooling system that can keep up.Changing the coolant every two years is good practice for any engine but especially so for these. BMW made a lot of improvements to the system over the N55.

If a car takes a long time to start it may be due to a bad high pressure fuel pump. This engine has two but one only turns on above 3000rpm.

Many of these engines will have been re-chipped by owners to make more power. That's not a bad thing, but beware of any that have been pushed a bit too far.

As with other direct injection engines the valves can accumulate carbon deposits on the back and this can greatly reduce intake flow, even in a forced induction engine. The only solution is to remove the intake manifold and walnut blast the carbon off. Even after 40,000 miles substantial deposits can form. Don't blame BMW, blame current emissions regulations. Fitting a catch can will help reduce this as gunk isn't recirculated.

You MUST regularly check the oil level, any oil starvation at all is going to get expensive very quickly. Don't even think of running the oil for the recommended service duration if you value your turbo. Change it sooner, use the best oil and replace the filter half way through the cycle. Buying one of these with no service history is asking for trouble.

Fitting an oil catch can rather than using BMW's oil separator is highly recommended and there are many after market options. It can be cheaper in the long run and boost reliability.