Tuning the BMW S38

"Comprehensive guide to tuning the BMW S38 engine!"

We often are getting messages inquiring about getting more power from the S38 and wanting to know what are the ultimate S38 mods that work. So let us look into BMW S38 parts and outline the best mods that work on this great engine and point out some frequent tuning mistakes along the way.

The BMW S38 offer good returns when tuned and with the best modified mods like a remap, turbo kits and camshafts you will substantially improve your driving fun.

In this article we review and look at S38 tuning and summarise the premier mods that work.

The best S38 mods on an engine are as we have found the ones that give the best value for money.

We won't be swayed by popular S38 mods, they need to be cost effective.

Altering your S38 cam will make a dramatic difference to the engine power band. Choosing a higher performance cam profile raises the power band accordingly.

NB: Fast road cams commonly raise the torque over the rev band, you may lose a little low down torque but the top end will improve.

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

On a car driven daily must carefully try to optimize your power band to your usage of the car.

I would be surprised if you have found a S38 Race cam is a pleasure to live with when driving around busy urban areas.

Some S38 engines respond better to more aggressive camshaft durations check your engine on a rolling road.

The ECU mapping and fuelling also will say much on the power gains you'll make.

A longer valve duration can alter the power 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.

S38 Tuning Stages

Stage 1 S38 modifications: Intake headers, Drilled & smoothed airbox, Fast road camshaft, Sports exhaust manifold, Remaps/piggy back ECU, Panel air filters.

Stage 2 S38 modifications: Sports catalyst & performance exhaust, fuel pump upgrades, Fast road cam, Ported and polished head, induction kit, high flow fuel injectors.

Stage 3 S38 modifications: Twin charging conversions, Competition cam, Crank and Piston upgrades to alter compression, Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting, Internal engine upgrades (head flowing porting/bigger valves).

The S38 engine blocks are fantastic to work on and thanks to their popularity there are quite a few choices of upgrades and tuning parts out there.

ECU mapping helps release the full potential of all the mods you've done to your S38.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but figures achieved often vary depending on the mods you've applied and the condition of your engine.

Feeding more fuel and air into each cylinder is the whole point to any performance tuning project.

Intake transmit the air from the filter and allow it to be sucked into the engine cylinders with fuel for the squish phase.

The bore size, shape and rate of flow of the Air Intake manifolds can make a big difference to to fuel atomisation on the S38.

We often see plenum chambers are needing a performance upgrade, although some manufacturers provide reasonably well designed plenum chambers.

Fitting big valve kits, doing some port matching and head flowing will also increase bhp, and importantly will raise potential for raising the bhp increase on other upgrades.

Turbo upgrades for the S38

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 S38

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

If a car has a turbo already fitted upgrades are giving better power gains and you'll see that turbo charged engines are made using harder and stronger components.

However every engines have limits

Research these restrictions and upgrade to higher quality crank and pistons to utilize the power.

We see many drivers spending a fortune on turbo charger upgrades on the S38 only to watch the engine block throw a rod just after it's been finished.

Big turbo chargers commonly experience no power at low rpm, and small turbo chargers spool up really quickly but won't have the high rpm engines power gains.

In recent times the market of turbo chargers is always improving and we commonly find variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbo chargers divert the exhaust flow into 2 channels and direct these at differently profiled vanes in the turbo charger. They also help the scavenging effect of the engine.

You'll commonly see there is a restriction in the air flow sensor AFM/MAF on the S38 when a lot more air is being pulled into the engine.

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

Adding a supercharger or additional turbo will make large power gains, although more difficult to install. We have this in depth look at twinchargers if you want to read more.

Uprating S38 fuel injectors

You will need to ensure that the engine is not starved of fuel so will have to ramp up the fuelling when you start extending past 20% of a bhp and torque increase.We strongly recommend you to be generous with your injector capacity.

The rule of thumb is to add 20% to the flow rate when fitting an injector, this allows for injector deterioration and provides 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.

Best S38 performance exhausts

You may need to boost your exhaust if your current exhaust is creating a flow problem.

On most factory exhausts you'll find the 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.

Please dont run with the largest exhaust you can find this will reduce the exhaust flow 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.

Common exhaust restrictions come around the filters installed, so adding a faster flowing race alternative will help avoid this restriction.

Problems and issues to look out for on the S38

The S38 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the S38, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your S38 engine please join us in our friendly forum where you can discuss tuning options in more detail with our S38 owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

We need your help to complete and improve this page, so do give us your feedback in the comments box below.

We really like hearing from our readers, and hearing about which mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our S38 guides and tips are kept up to date.

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