Tuning the Mercedes M103

"Comprehensive guide to tuning the Mercedes M103 engine!"

We are frequently getting emails about the optimum M103 modifications. So let us look into Mercedes M103 mods and outline the best modifications on this great engine and point out some frequent tuning mistakes along the way.

Let us review M103 tuning and outline the optimum mods that work. Mercedes M103 have loads of potential and with a few sensible tuning enhancements like remaps, turbo upgrades and camshafts you will really maximise your driving pleasure.

Just because particular tuning parts are are common on M103 it doesn't mean its worth having, instead we will concentrate) on the top tuning parts that will give your M103 the best power gain for you spend.

The cam profile plays a big part in the engines power output so cam upgrades make quite a large difference. The intake & exhaust durations will alter depending on the chosen cam profile, so large power band gains are on offer for cam upgrades.

NB: Fast road cams usually push up the torque throughout the rev range, you might lose a little low down power but high end rpm power will be higher.

Race cams, push up the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Race camshaft won't do well if driving around busy urban areas.

You should ideally match your power band to your typical driving style so for a daily driver stick with a fast road M103 camshaft

Some M103 engines respond better to more aggressive camshaft durations check your engine on a rolling road.

The ecu map and fuel pump and injectors also have a large bearing on the bhp gains you'll get.

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.

M103 Tuning Stages

Stage 1 M103 modifications: Fast road camshaft, Remaps/piggy back ECU, Sports exhaust manifold, Panel air filters, Intake headers, Drilled & smoothed airbox.

Stage 2 M103 modifications: fuel pump upgrades, Fast road cam, Sports catalyst & performance exhaust, Ported and polished head, induction kit, high flow fuel injectors.

Stage 3 M103 modifications: Internal engine upgrades (head flowing porting/bigger valves), Twin charging conversions, Competition cam, Crank and Piston upgrades to alter compression, Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting.

Mapping will help unlock the full potential of all the tuning parts you've done to your M103.

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

Pulling air and fuel into each cylinder is the main goal to any engine modification job.

Air Intake manifolds take the air from the intake filter and allow it to be pulled into the engine and mixed with fuel.

Shape and rate of flow of the Air Intake manifolds can make a noticeable difference to to fuel mixing and power on the M103.

Commonly we find the air intake manifolds are in desperate need of performance upgrades, although a few car makers provide fairly well optimized air intake manifolds.

Big valve conversions on the M103, carrying out 3 or 5 angle valve jobs and porting and head flowing will also raise torque, the fantastic side effect is it will allow you to get an improved torque increase on other upgrades.

Turbo upgrades for the M103

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 M103

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

When the engine is fitted with a turbocharger tuning parts are going to net you a larger power gain and you'll see that turbocharged engines are made using stronger components.

However most engines will need better parts at higher power limits

It is important to find these limitations and install more solid crank and pistons to survive the power.

There are many people spending a loads on turbocharger upgrades on the M103 only to see the car explode just after it's used on the roads.

Large upgraded turbochargers tend to suffer a bottom end lag, and low capacity turbochargers spool up more quickly but do not have the top end bhp gains.

Thankfully the selection of turbos is always improving and we are seeing variable vane turbos, permitting the vane angle is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbos divert the exhaust flow into 2 channels and push these at differently profiled vanes in the turbo. 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 the M103 when a lot more air is being fed into the engine.

We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited performance at a much lower level.

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

Uprating M103 fuel injectors

You will need to ensure that the engine is not starved of fuel so must increase the fuelling when you start exceeding 20% of a performance increase.Don't forget to be generous with your flow rate on the injectors.

The accepted safe increase is to add 20% capacity when buying an injector, this accounts for injector deterioration and gives you some 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.

Best M103 performance exhausts

Only look to increase your exhaust if your exhaust is creating a restriction.

On most factory exhausts you should find that your flow rate is still fine 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 equal out the flow of gases through the engine.

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

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

Problems and issues to look out for on the M103

The M103 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the M103, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your M103 engine please join us in our friendly forum where you can discuss tuning options in more detail with our M103 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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This article is flagged for an update, so please pass on specific tips below that I can include. All articles, and content was written by me, Waynne Smith TorqueCars founder. Some outlines are just too general so I appreciate your feedback and suggestions. This entry was filed under Mercedes. You can leave a response below or join our forum to discuss this article and car modification in detail with our members.

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