Mercedes M103 Tuning

"All you need to know about tuning the Mercedes M103 engine!"

The Mercedes M103 are fantastic to work on and with carefully chosen motorsport upgrades like remapping, turbo upgrades and camshafts you will greatly maximize your driving opportunities.

Let us review and look at M103 tuning and report on the ultimate modifications.

History, Power & Specs of the Engine

103.980 3.0 L

With CIS-E (Continuous Injection System - Electronic).

  • (179 PS; 177 hp) @ 5700 rpm,  255Nm (188lbft) @ 4400 rpm (with cat)
  • (190 PS; 188 hp) @ 5700 rpm 255Nm (188lbft)  260Nm (192lbft) @ 4400 rpm

103.940 2.6L

With the CIS-E engine management system.

  • (160 PS; 158 hp)@ 5800 rpm 220Nm (162lbft) @ 5800 rpm with cat
  • (169 PS; 166 hp) @ 5800 rpm 228Nm (168lbft)@ 5800 rpm

Tuning the Mercedes M103 and best M103 performance parts.

Best M103 parts

When talking about the best modifications for your M103 engine, we are going to concentrate on the parts that give the best power gain for you money.

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

Fast road camshafts normally increase the bhp through the rpm range, you may lose a little low end torque but the high end rpm power will improve.

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

A Motorsport and race camshaft is not great driving in heavy traffic.

You should ideally match your torque band to your preferences so for a daily driver stick with a fast road M103 camshaft

Each engine responds better to different camshaft durations check your engine on a rolling road.

The map and injectors and fuel pump 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.

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Best Engine Mods for your car

  1. Engine Tunes - engine tuning/remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.

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

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

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


Carefully think through your options and then acquire your parts and set yourself a power target to void expensive mistakes.


Remaps allows a tuner to unlock the full potential of all the mods you've done to your M103.

(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 NA (naturally aspirated) engines, but power output usually depend much on the mods you've fitted and the condition of your engine.

Pushing air and fuel into your M103 is the whole point to any car tuning project.

Air Intake manifolds carry the air from the filter and allow it to be drawn into the engine cylinders.

Design and rate of flow of the Intake manifold can make a substantial difference to fuel atomisation and engine efficiency on the M103.

On popular production engines intake manifold are in desperate need of motorsport parts, although some OEM provide fairly well optimized intake manifold.

Fitting big valve kits, carrying out M103 port enlargement and head flowing will also raise power, and significantly will give you increasing the power increase on other parts.

Turbo upgrades

NA (naturally aspirated) 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 impressive power gains.

When your car has a turbo already fitted modifications are going to net you a larger power gain and turbocharged engines will have stronger components.

However you will find an engines have weakspots

We recommend you find these limitations and fit better pistons and crank to cope with the power.

There are many people spending a lots of money on turbo upgrades on the M103 only to see the M103 catastrophically fail just after it's used in anger.

Larger turbo units will usually experience low end lag, and smaller turbo units spool up more quickly but won't have the top end engines power gains.

In recent times the choice of turbo chargers is always improving and we now see variable vane turbo chargers, allowing the vane angle is altered according to speed to lower lag and increase top end bhp.

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

You'll commonly see there is a limit in the air flow sensor AFM/MAF on the M103 when loads 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 was restricting performance at a much lower level.

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


When you raise the torque you will need to pay attention to the fuelling.


More torque needs more fuel. We strongly recommend you to over specify your injector capacity.

The accepted safe increase is to add another 20% when specifying an injector, this allows for injector deterioration and allows 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.


You should look to replace your exhaust if the current exhaust is actually causing a flow problem.

On most factory exhausts you'll see your 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 increase the flow of gases through the engine.


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

Usual exhaust restrictions can be located the catalysts installed, so adding a higher flowing high performance aftermarket one will improve air flow, and rather than doing an illegal decat, will keep the car road legal.

Weak spots, Issues & problem areas on the M103

The M103 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.

Oil leaks have been noted on many M103 engines.

Keep an eye on the timing chain, head gaskets (especially if the engine overheats) and the fuel injection system. If you notice rattles or bad idling get these sorted before they cause major issues.

Regular oil changes are vital on the M103, especially when tuned and will help extend the life and reliability of the engine.

If you would like to know more, or just get some friendly advice 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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