BMW S55 Tuning

"All you need to know about performance parts and tuning the BMW S55 engine!"

In this article we review and look at S55 tuning and show the premier upgrades. BMW S55 are awesome to work on and with the right performance mods like remapping, turbo upgrades and camshafts you will noticeably maximise your driving fun.

The high redline and twin turbos make this straight six feel like a much larger engine with a near instant power delivery at all points of the rev band.

By dropping the V8 and going to a straight 6 BMW were in line for much criticism, but the jaw dropping performance of the S55 silenced those critics, and the improved fuel economy shut up green campaigners.

We outline options for your S55 tuning and highlight the greatest upgrades.

History, Power & Specs of the Engine

It replaced the NASP S65 and is based on the N55, but gets a pretty high state of tune, stronger pistons, a twin turbo setup and needed a couple of fuel pumps to deliver the required fuel.

205 kW (275 bhp) - 268 kW (359 bhp)

  • 2020-present F87 M2 CS Racing

302 kW (405 bhp)

  • 2018-present F87 M2 Competition

317 kW (425 bhp) 550 Nm (406 lbft) at 1,850-5,500 rpm

  • 2014-2018 F80 M3
  • 2014-present F82/F83 M4

331 kW (444 bhp)

  • 2016-2018 F80 M3 with Competition package(
  • 2016-present F82/F83 M4 with Competition package
  • 2020 F87 M2 CS

338 kW (453 bhp)

  • 2018 F80 M3 CS
  • 2017-present F82 M4 CS

368 kW (493 bhp)   600 Nm (443 lbft

Water injection system allowed the boost pressure to be increased to 21.6 psi (1.49 bar).

  • 2015-2016 F82 M4 GTS
  • 2017 F82 M4 DTM Champion Edition

Tuning the BMW S55 and best S55 performance parts.

Best S55 tuning mods

The greatest S55 parts on an engine are typically the ones that give the biggest return for your cash.

We won't be swayed by popular S55 parts, they need to be cost effective.

Significant gains on the S55 can be made from cam upgrades. Altering the cam profile alters the intake and exhaust durations on the engine and can dramatically change the power band and power output.

Fast road camshafts tend to raise the bhp and torque across the rpm band, you may sacrifice a little bottom end torque but top end will be lifted.

Race camshafts, raise the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Motorsport and race cam makes it harder when on the daily commute, because the lumpy idle will make the car prone to stall and smooth driving at low rpm becomes impossible. If you are developing a track car this doesn't matter as you are in the high end of your RPM range anyway and that is where you want the power to be.

You should ideally optimize your torque band to your driving style so for a typical daily driver stick with a fast road S55 cam

Each engine responds better to extreme camshaft durations than others.

The ecu map and injectors and fuel pump also will say much on the torque gains you'll hit.

Extending exhaust or intake durations can alter the torque band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

Typical stage 1 mods often include: Fast road camshaft, Panel air filters, Sports exhaust manifold, drilled & smoothed airbox, Remaps/piggy back ECU, Intake headers.

Typical stage 2 mods often include: high flow fuel injectors, Sports catalyst & performance exhaust, induction kit, fuel pump upgrades, Ported and polished head, Fast road cam.

Typical stage 3 mods often include: Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Crank and Piston upgrades to alter compression, Internal engine upgrades (head flowing porting/bigger valves), Engine balancing & blueprinting, Twin charging conversions.

Review your options and then find your mods and set yourself a power target to avoid disappointment.

ECU mapping will help release the full potential of all the tuning parts you've fitted to your S55.

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

It will usually give you around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but power output usually differs on the tuning parts you've carried out and the condition of your engine.

Shoving more air into the S55 engine is the whole point to any performance tuning job.

Headers flow the air during the suck phase from the filter and allow it to be fed into the engine cylinders with fuel for the squish phase.

The shape and flow characteristics of the Air Intake manifolds can make a large improvement to fuel atomisation on the S55.

It's not uncommon that intake headers are ripe for a performance upgrade, although some OEM provide well optimised intake headers.

Increasing the S55 valve size, doing some port work and head flowing will also increase bhp and torque, and significantly will allow you to get a better bhp and torque increase on other modifications.

Turbo upgrades

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes significant power gains.

If an engine is turbo charged mods are giving better power gains and you'll see that turbo charged engines already contain harder and stronger components.

However you will find an engine has limits, even though the S55 limits are double what most engines can handle.

The stronger crank and lighter crankshaft were probably where the tuner would start if they had the N55, then BMW added an additional fuel pump and active exhaust system.

We see many car owners spending a lots of money on turbo upgrades on the S55 only to see the engine catastrophically fail when it's been completed. We note  that water injection has been used to keep the intake temps down and avoid detonation, so this is worth considering on higher states of tune, or larger turbos.

Big capacity turbo units often suffer low end lag, and low capacity turbo units spool up quickly but do not have the top end bhp gains. Often a twin turbo setup is replaced with a single large turbo, and this will help attain large top end power figures.

In recent times the world of turbos is always evolving and we now see variable vane turbos, permitting the vane angle is altered according to speed to lower lag and increase top end bhp and torque. BMW have used cutting edge turbo tech on this engine but we are eagerly waiting to see what the turbo specialists can come up with in the next few years to improve on this.

Twin scroll turbos divert the exhaust flow into a couple of channels and push these at differently profiled vanes in the turbocharger. They also boost the scavenging effect of the engine.

It is common that there is a limitation in the air flow sensor MAF/MAP on these engines when loads more air is being fed into the engine.

We see 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more challenging to configure. We have this article on twincharging if you want to read more.

Water injection was used to reach the 493hp by lowering the intake temps and allowing higher boost pressure.

Fuelling

Don't dismiss the need look at the fuel delivery when you are increasing the torque - it makes the car more thirsty. We would recommend you to over specify your flow rate on the injectors.

The accepted safe increase is to add 20% to the flow rate when specifying an injector, which takes into account injector deterioration and allows a little spare capacity should the engine need more fuel.

We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

BMW took fuelling to new levels in the S55 with a twin fuel pump setup to help the twin turbos guzzle as much fuel as your right foot demands. It is unlikely that most of our members will hit fuelling issues unless they were planning a competition build from their S55.

Exhaust

You may need to upgrade your exhaust if the current exhaust is creating a restriction.

One of the big gripes people have with the S55 is that it doesn't sound all that exciting when driven hard.

Adding a better exhaust resonator will change the exhaust note and improve this but louder and better sounding does not mean more power and we're here to talk power.

On most factory exhausts you'll find your flow rate is fine even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Don't go with the widest exhaust you can source you'll slow the exhaust rate - the best exhausts for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions can be traced to the catalysts installed, so adding a faster flowing race alternative such as a sports catalyst pretty much removes this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed, but keeps the car road legal.

Weak spots Issues & problem areas on the S55

The engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.

Carbon build up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to this engines design, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

Regular oil changes are vital on the S55 , especially when tuned and will help extend the life and reliability of the engine.

A limited number of S55 owners have had an issue with the bolt on the crank failing. This is usually the friction washer causing it to slip.

If you would like to know more, or just get some friendly advice on Tuning your engine please join us in our friendly forum where you can discuss tuning options in more detail with our S55 owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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Your Constructive comments on this article




2 Responses to “S55 Tuning”

  1. Sam grossman says:

    Question since you are very knowledgable on the S55 motor.
    I’m having an issue:
    2018 F80 M3 Stock

    Car is knocking Under 3K RPM and not pushing any timing over 6 deg.
    It is not fuel related. (Added 25% E85 to raise Octane level )
    No boost leaks.
    New Spark plugs / Coils
    New fuel injectors.
    No CEL
    Any suggestions on where to start looking to resolve this issue ?
    I Datalog the car constantly and something is definitely not right. Loss torque as well.
    Your thoughts on where to start or what it might be ?
    Thank you Sir !!! 🙏🙏🙏

    • TorqueCars says:

      I’d check the air intake sensors and the lambda just in case it’s one of those playing up. If you whip out the air filter do you still have the issue? Could be intake related potentially. Carbon build up could cause similar issues, choking the engine of air forcing it to cut back on fuel and timing to compensate.

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