Mercedes M278 Tuning

"All you need to know about performance tuning the Mercedes M278 engine!"

TorqueCars will review M278 tuning and point out the optimum mods that work. Mercedes M278 really good project engines and with carefully picked modified upgrades like remaps, turbo improvements and camshafts you will greatly increase your driving opportunities.

History, Power & Specs of the M278 Engine


  • 429 bhp 435 PS at 5,250 rpm 700 Nm 516lbft
  • 402 bhp 408 PS 600 Nm 443lbft at 1,600 rpm
  • 362 bhp 367 PS and 550 Nm 406lbft
  •  449 bhp 455 PS at 5,250 rpm 700 Nm 516 lbft  1,800-3,500 rpm

The M278 was fitted in the following models

  • 2011–2017 Mercedes-Benz S-Class S
  • 500 in Europe
  • S550 in the US
  • 2011–2014 Mercedes-Benz CL-Class
  •  CL500 in Europe,
  • CL550 in the US
    2015-2017 Mercedes-Benz S-Class Coupe/Cabriolet
  •  S500 in Europe,
  • S550 in US
    2011–2018 Mercedes-Benz CLS-Class
  • CLS500 in Europe
  • CLS550 in the US
  • 2012–2020 Mercedes-Benz SL-Class
  • SL500 in Europe
  • SL550 in the US
  • 2012–2014 Mercedes-Benz E-Class
  • E500 in Europe
  • E550 in the US
  • 2012-2014 Mercedes-Benz M-Class
  • GLE-Class
  • ML500 in Europe
  • ML550 in US
  • 2013–2014 Mercedes-Benz GL-Class
  • GL450 in Europe and US
  • 2013–2019 Mercedes-Benz GL-Class
  • GLS-Class GL500
  • GLS500 in Europe
  • GL550/GLS550 in the US

2016–present BAIC BJ90 an SUV from Chinese brand BAIC based on the second generation Mercedes-Benz GL-Class

Tuning the Mercedes M278 and best M278 performance parts.

Best M278 upgrades

When talking about the greatest modifications for your M278 engine, we are going to focus on the upgrades that give the biggest return for your cash.

Altering your M278 cam will make a dramatic difference to the engine engines power. Choosing a higher performance cam profile raises the engines power accordingly.

Fast road camshafts commonly raise the power through the rev range, you might lose a little low down torque but the top end will be better.

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

A Motorsport and race camshaft makes it harder when driving around busy urban areas. This is because a competition cam causes a very lumpy idle, and makes the car more prone to stall or jerk along in stop start traffic, sadly though many ignore this and end up ruining a perfectly good car and having to revert back to a fast road, or OEM cam profile.

You should ideally optimize your bhp range to your driving style so for a typical daily driver stick with a mild fast road M278 camshaft

Some M278 engines respond better to more aggressive cam durations so set your engine up on a rolling road.

The engine timing and injectors and fuel pump also will make differences on the power gains you'll achieve.

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

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

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

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

    ECU flashing helps release the full potential of all the mods you've done to your M278.

    (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 the outcome often differs on the mods you've done and the condition of your engine.

    It is the main goal to any engine modification project to feed air and fuel into each cylinder

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

    Design and rate of flow of the Air Intake manifolds can make a noticeable improvement to fuel atomisation on the M278.

    I usually find intake are in dire need of aftermarket tuning parts, although some car makers provide fairly well optimized intake.

    Larger M278 valves, carrying out 3 or 5 angle valve jobs and porting and head flowing will also improve torque, this will permit increasing the torque increase on other parts.

    M278 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 M278

    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.

    When your car is turbo charged upgrades are simpler to install and we find turbo engines are built using strengthened components.

    However you will find engines will need better parts at higher power limits.We recommend you find these restrictions and fit higher quality crank and pistons to handle the power.

    It's not unheard of tuners spending a lot of money on turbocharger upgrades on the M278 only to suffer the humiliation of seeing the engine literally blow up just after it's been finished.

    Big turbos tend to suffer a bottom end lag, and smaller turbos spool up quickly but won't have the peak rpm torque gains.

    Thankfully the choice of turbochargers is always moving on and we are seeing variable vane turbochargers, permitting the vane profile is altered according to speed to lower lag and increase top end performance.

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

    It is not unusual that there's a restriction in the air flow sensor AFM/MAP on the M278 when considerably 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 bhp at a much lower level.

    Adding a supercharger or additional turbo will make large bhp and torque gains, although more challenging to get working. We have this article on twincharging if you want to read more.


    You will need to ensure that the engine is not starved of fuel so need to increase the fuelling when you start exceeding 20% of a power increase.We strongly recommend you to be generous with your injectors flow rate.

    The accepted safe increase is to add 20% to the flow rate when buying an injector, helps cope with injector deterioration and affords 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.M278 Performance Exhausts

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

    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.

    Note that with the largest exhaust you can source you'll slow up the exhaust flow rate - the best 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 are in the catalyst installed, so adding a faster flowing sports alternative is the answer. This keeps the car road legal and will flow much better due to it's higher internal surface area and design, so has the added benefit of keeping your car road legal. The alternative decat should be considered an off road only mod, as removing a catalyst is illegal in most territories and regions for road registered cars..

    Weak spots, Issues & problem areas on the M278

    The M278 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 M278, 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 M278 engine please join us in our car forums where you can discuss M278 tuning options in more detail with our M278 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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