Mercedes M155 Tuning

"All you need to know about tuning the Mercedes M155 engine!"

We shall look at M155 tuning and outline the optimum mods that work. Mercedes M155 really good project engines and with the optimum motorsport parts like remapping, turbo upgrades and camshafts you will positively improve your driving pleasure.

History, Power & Specs of the M155 Engine

M155 SLR

  • 2004 Mercedes-Benz SLR McLaren
  • 2006¬†Mercedes-Benz SLR McLaren 722 Edition

617 bhp 626 PS 460 kW at 6,500 rpm  780 Nm 575lbft at 3,250 rpm.
641 bhp 650 PS 478 kW at 6,500 rpm 820 Nm 605lbft at 4,000 rpm (722 edition)

Tuning the Mercedes M155 and best M155 performance parts.

Best M155 parts

When talking about the greatest modifications for your M155 engine, we are going to concentrate on the ones that give the best value for money.

Significant gains on the M155 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.

Fast road cams tend to push up the bhp throughout the rev range, you may lose a little bottom end bhp but higher rpm power will be better.

Motorsport and race cams, push up the higher 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 on the daily commute, because the lumpy idle will make the car prone to stall and smooth driving at low rpm becomes impossible. If you are developing a track car this doesn't matter as you are in the high end of your RPM range anyway and that is where you want the power to be.

You should ideally optimize your bhp range to your usage of the car so for a road car stick with a shorter duration M155 camshaft

Some M155 engines respond better to different cam durations check your engine on a rolling road.

The map and fuelling also will say much 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.

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

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

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

    The M155 engines respond well to upgrades and we note that there is a growing number of upgrades and performance parts about.

    ECU mapping should help to release the full potential of all the tuning parts you've done to your M155.

    (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 often rely on the tuning parts you've fitted and the condition of your engine.

    Forcing air into your M155 is the aim to any tuning project.

    Intake Manifolds carry or channel the air from the filter and allow it to be drawn into the engine cylinders with fuel for the squish phase.

    Structure and rate of flow of the Intake manifold can make a large difference to fuel engine efficiency on the M155.

    Most intake manifolds are crying out for a performance upgrade, although some manufacturers provide reasonably good intake manifolds.

    Larger M155 valves, carrying out 3 or 5 angle valve jobs and porting and head flowing will also raise torque, and as an added benefit will permit increasing the torque increase on other mods.

    M155 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 M155

    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 your car is turbocharged, tuning parts are more reliable and you will discover turbo charged engines are built with more solid components.

    However most engines will have power limits.Discover these limitations and install better quality crank and pistons to survive the power.

    There are many drivers spending a fortune on turbo charger upgrades on the M155 only to suffer the humiliation of seeing the engine block go up in smoke soon after it's completed.

    Big upgraded turbos tend to suffer a bottom end lag, and small turbos spool up quickly but won't have the high rpm engines power gains.

    We are pleased that the choice of turbochargers is always improving and we commonly find variable vane turbochargers, where the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

    Twin scroll turbochargers divert the exhaust flow into 2 channels and direct these at differently designed vanes in the turbocharger. They also help the scavenging effect of the engine.

    It is common that there is a limitation in the air flow sensor AFM/MAP on the M155 when loads more air is being drawn into the engine.

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

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


    When you improve the performance you will need to uprate to the fuel delivery.

    More performance needs more fuel. We would recommend you to be generous with your flow rate on the injectors.

    As a rule of thumb add 20% when fitting an injector, this takes into account injector deterioration and allows a little 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.

    M155 Performance Exhausts

    Only look to boost your exhaust if your current exhaust is creating a restriction.

    On most factory exhausts you'll see 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 will certainly help air flow from the engine but do not go too large or you might just stuff your flow rate and make things worse. So generally speaking, keep to a size of 1.5 to 2.5 inches for best results.

    Typically exhaust restrictions are traced to the filters installed, so adding a faster 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 M155

    The M155 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.

    Regular oil changes are vital on the M155, 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 M155 engine please join us in our car forums where you can discuss M155 tuning options in more detail with our M155 owners. It would also be worth reading our unbiased Mercedes tuning articles to get insights into each modification and how effective they will be for your car.

    Please help us improve these tips by sending us your feedback in the comments box below.

    We love to hear what our visitors have got up to and which upgrades work best for you on your car. Which helps us keep our guides and tips up to date helping others with their modified car projects. Your feedback and comments are used to keep this page up to date, and help improve the accuracy of these M155 tuning guides which get regular updates and revisions.

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