Tuners tips on "BMW S55 Tuning"

BMW S55 Tuning Guide

"Modifying the BMW S55 engine!"

The BMW S55 make a good tuning project and with the right motorsport parts like ECU maps, turbo kits and camshafts you will substantially improve your driving fun.

Our aim here is to outline options for your S55 tuning and highlight the premier modifications.

When talking about the optimum parts for your S55 engine, we are going to concentrate on the upgrades 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 torque and power output.

NB: Fast road camshafts normally raise the torque through the rev range, you may sacrifice a little low end power but your higher rpm power will be lifted.

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

In a road car should ideally to match your torque band to your cars usage.

I would be surprised if you have found a S55 Motorsport camshaft is a pleasure to live with when driving in heavy traffic.

Different S55 engines respond better to mild camshaft durations than others.

The ecu map and fuel pump and injectors also have an effect on the bhp gains you'll achieve.

Extending exhaust or intake durations can alter the bhp 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 mods: Drilled & smoothed airbox, Sports exhaust manifold, Fast road camshaft, Remaps/piggy back ECU, Intake headers, Panel air filters.

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

Stage 3 mods: Internal engine upgrades (head flowing porting/bigger valves), Engine balancing & blueprinting, Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Crank and Piston upgrades to alter compression, Twin charging conversions.The S55 engines respond well to mods and thankfully there is a growing number of parts and tuning parts around.

Mapping allows a tuner to fully realize the full potential of all the modifications you've done 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 the end result will vary depending on the modifications you've done and the condition of your engine.

Forcing more air and fuel into the S55 engine is the whole point to any tuning task.

Intake transmit the air from the filter and allow it to be drawn into the engine and mixed with fuel.

The shape and flow characteristics of the Intake manifold can make a noticeable difference to to fuel atomisation and engine efficiency on the S55.

Many mass produced engine headers are ripe for aftermarket tuning parts, although some manufacturers provide well optimised headers.

Adding a S55 larger valve kit, carrying out 3 or 5 angle valve jobs and porting and head flowing will also lift performance, the fantastic side effect is it will make space for increasing the performance increase on other parts.

S55 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

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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 an engine is turbocharged, mods are going to net you a larger power gain and you'll see that turbocharged engines will have many forged and stronger components.There are weak spots for every engine, with some being very over engineered and some just sufficiently able to handle stock power

Discover these limitations and upgrade to forged components to utilize the power.

We see many people spending a loads on turbo charger upgrades on the S55 only to have the car catastrophically fail when it's finished.

Larger capacity turbo chargers will usually suffer no power at low rpm, and smaller turbo chargers spool up much more quickly but do not have the peak rpm power band gains.

Thanks to new tech the choice of turbochargers is always moving on and we now see variable vane turbochargers, allowing the vane profile is altered according to speed to lower lag and increase top end bhp.

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

You'll commonly see there is a limitation in the air flow sensor MAP/MAF/AFM on the S55 when a lot 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 limited bhp and torque at a much lower level.Adding a supercharger or additional turbo will make large bhp gains, although more complex to get working. We have this in depth look at twinchargers if you want to read more.

S55 Fuelling upgrades and mods

You will need to ensure that the engine is not starved of fuel so need to look at the fuelling when you start going beyond 20% of a bhp increase.

It makes sense to over specify your flow rate on the injectors.

The rule of thumb is to add 20% when fitting an injector, this allows for injector deterioration and affords a bit of spare capacity should the engine require 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.

S55 Exhaust upgrades and modifications

You only need to to boost your exhaust if your current exhaust is creating a restriction in flow.

On most factory exhausts you should find that the flow rate is still ok 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 increase the flow of air through the engine.

But if the exhaust pipe is too large, ie: over 2.5 inches bore, you will lose a lot of the flow rate and end up losing power and torque.

Usual exhaust restrictions are in the emissions filters installed, so adding a faster flowing race alternative will help avoid this restriction.

S55 Issues & common problems

The S55 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.

For more information on Tuning your S55 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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