Tuning the BMW S55

"Comprehensive guide to performance tuning the BMW S55 engine!"

The BMW S55 are awesome to work on and with the right uprated parts like remapping, turbo upgrades and camshafts you will greatly maximise your driving opportunities.

This pages aim is provide a guide to S55 tuning and show the optimum upgrades.

When talking about the best best for your S55 engine, we are going to focus on the modifications that give the best value for money.

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.

NB: Fast road camshafts commonly boost the torque through the rpm band, you could drop a little bottom end power but top end will be lifted.

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

On a typical daily driver you need to match your bhp range to your cars usage.

I'd be amazed if you have found a S55 Race cam is a pleasure to live with when on the daily commute.

Some S55 engines respond better to mild cam durations check your engine on a rolling road.

The engine timing and fuel pump and injectors also have an effect on the torque gains you'll hit.

A longer valve duration 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.

Stage 1 modifications: Remaps/piggy back ECU, Panel air filters, Fast road camshaft, Intake headers, Drilled & smoothed airbox, Sports exhaust manifold.

Stage 2 modifications: Ported and polished head, induction kit, Sports catalyst & performance exhaust, fuel pump upgrades, Fast road cam, high flow fuel injectors.

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

The S55 power plant respond well to upgrades and we see that there are increasing numbers of mods and tuning parts out there.

Remaps allows a tuner to release the full potential of all the tuning mods you've fitted to your S55.

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

It is vital to any engine performance tuning project to pull more fuel and air into the S55 engine

Headers take the air from the filter and allow it to be pulled into the engine cylinders.

The size of bore and shape and rate of flow of the Plenum can make a substantial change to fuel mixing and power on the S55.

On popular production engines intake headers are crying out for a performance upgrade, although some car makers provide well optimised intake headers.

Adding a S55 larger valve kit, doing a bit of port work and head flowing will also lift power, and significantly will allow you to get a greater power increase on other parts.

Turbo upgrades

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your S55

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

When the engine is fitted with a turbocharger parts are relatively easy and you'll see that turbo charged engines are built with strengthened components.

However engines have limits

It is important to find these limits and install better pistons and crank to utilize the power.

There are many people spending a loads on turbo upgrades on the S55 only to suffer the indignity of watching the whole thing throw a rod just after it's used in anger.

Larger upgraded turbos tend to experience low end lag, and little turbos spool up much more quickly but don't have the peak end power band gains.

Thanks to progress the choice of turbo units is always developing and we now see variable vane turbo units, permitting the vane profile is altered according to speed to lower lag and increase top end torque.

Twin scroll turbo units divert the exhaust gases into 2 channels and direct these at differently designed vanes in the turbocharger. They also boost the scavenging effect of the engine.

It is not unusual that there is a limit in the air flow sensor MAF/MAP on the S55 when loads more air is being drawn into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped power at a much lower level.

Adding a supercharger or additional turbo will make large bhp gains, although more challenging to install. We have this feature on twinchargers if you want to read more.

Fuelling upgrades and mods

You will need to ensure that the engine is not starved of fuel so need to ramp up the fuelling when you start going beyond 20% of a bhp increase.It is important to be generous with your flow rate on the injectors.

As a rule of thumb add 20% when fitting an injector, helps cope with injector deterioration and gives you some 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.

Exhaust upgrades and mods

Only look to upgrade your exhaust if the existing exhaust is creating a restriction.

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

Sports exhausts will certainly help air flow through the engine but avoid an exhaust that is too wide or you may end up will reduce the flow rate. Stick to 1.5 to 2.5 inches for best results.

Common exhaust restrictions come around the catalysts installed, so adding a better flowing high performance alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the S55

The engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the S55 , particularly when the engine has been modified and is putting down more power than the manufacturer intended.

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.

For more information 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.

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) version

  • 2020-present F87 M2 CS Racing

302 kW (405 bhp) version

  • 2018-present F87 M2 Competition

317 kW (425 bhp) version

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

331 kW (444 bhp) version

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

338 kW (453 bhp) version

  • 2018 F80 M3 CS(23]
  • 2017-present F82 M4 CS

368 kW (493 bhp) version

water injection system allows the boost pressure to be increased to 21.6 psi (1.49 bar).

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

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