Mercedes M158 Tuning

"All you need to know about tuning the Mercedes M158 engine!"

This pages aim is review and look at M158 tuning and summarise the premier modifications.

Mercedes M158 are fantastic to work on and with the best sports enhancements like a remap, turbo kits and camshafts you will noticeably enhance your driving experience.

History, Power & Specs of the M158 Engine


537 kW 720 hp at 5800 rpm and 1,000 Nm 738lbft at 2250-4500 rpm

2012–present Pagani Huayra

Tuning the Mercedes M158 and best M158 performance parts.

Best M158 tuning parts

Just because particular tuning parts are are common on M158 it doesn't mean its worth having, so we'll best tuning parts that will give your M158 the best value for money to power increase.

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

Fast road cams normally push up the bhp through the rpm range, you might lose a little bottom end bhp but your higher rpm power will be higher.

Motorsport 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 Competition 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 match your bhp range to your typical driving style so for a car used daily stick with a mild fast road M158 camshaft

Some M158 engines respond better to mild camshaft durations so view each engine as unique.

The ecu map and fuel pump and injectors also will say much on the power gains you'll achieve.

Altering valve durations 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.

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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, Fast road camshaft, Remaps/piggy back ECU, Panel air filters, Intake manifolds, Sports exhaust header/manifold.

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

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

    Plan your options and then buy your parts and set yourself a power target to avoid wasting your time and money.

    ECU mapping should help to fully realize the full potential of all the parts you've done to your M158.

    (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 your mileage usually vary depending on the parts you've carried out and the condition of your engine.

    Feeding more air into the M158 engine is vital to any engine tuning task.

    Intake manifolds take the air during the suck phase from the filter and allow it to be fed into the engine and mixed with fuel.

    Shape and flow rate of the Air Intake manifolds can make a substantial improvement to fuel engine efficiency on the M158.

    It's not uncommon that manifolds are ripe for aftermarket tuning parts, although a few OEM provide reasonably good headers.

    Larger M158 valves, doing some port matching and head flowing will also increase bhp, and significantly will make space for raising the bhp increase on other tuning parts.

    M158 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 M158

    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.

    If the engine is turbo charged parts are going to net you a larger power gain and we find turbocharged engines are made using harder and stronger components.

    However every engines will need better parts at higher power limits.See where you'll find these restrictions and install better quality components to handle the power.

    There are many people spending a loads on turbo charger upgrades on the M158 only to watch the engine literally blow up on it's first outing after it's used in anger.

    Bigger turbo units tend to experience a bottom end lag, and low capacity turbo units spool up much more quickly but don't have the top end bhp gains.

    We are pleased that the range of turbo units is always moving on and we now see variable vane turbo units, permitting the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

    Twin scroll turbo units divert the exhaust flow into two channels and feed these at differently angled vanes in the turbo charger. They also help the scavenging effect of the engine.

    It is common that there is a limitation in the air flow sensor MAP/MAF/AFM on the M158 when considerably more air is being sucked into the engine.

    Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped bhp 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.


    Don't omit to uprate the fuel system when you are increasing the bhp and torque - it makes the car more thirsty. We would recommend you to be generous with your injectors flow rate.

    The accepted safe increase is to add 20% to the flow rate when specifying an injector, this takes into account 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.M158 Performance Exhausts

    Only look to improve your exhaust if the current exhaust is actually causing a restriction in flow.

    On most factory exhausts you'll find your flow rate is 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 air through the engine.

    But if the exhaust is too big, ie: over 2.5 inches bore, you will lose a great deal of your flow rate and end up losing power and torque.

    Typically exhaust restrictions can be traced to the catalysts 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 M158

    The M158 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 M158, 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 M158 engine please join us in our car forums where you can discuss M158 tuning options in more detail with our M158 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.

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    We love to hear what our visitors have got up to and which modifications 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 M158 tuning guides which get regular updates and revisions.

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