Mercedes OM656 Tuning

"All you need to know about tuning the Mercedes OM656 engine!"

The Mercedes OM656 are popular engines and with carefully chosen uprated tuning mods like a remap, turbo kits and camshafts you will substantially increase your driving enjoyment.

Here we outline options for your OM656 tuning and point out the optimum upgrades.

History, Power & Specs of the OM656 Engine

Om656 diesel engine specs and power

OM656 D29T R SCR

  • 210 kW (286 PS; 282 hp) at 3,400–4,600 rpm 600 Nm (443 lbft) at 1,200–3,200 rpm

Fitted to the...

  • 2017–present W222 S 350 d
  • 2018–present C257 CLS 350 d
  • 2018–present W213 E 350 d
  • 2018–present W463 G 350 d
  • 2019–present V167 GLE 350 d
  • 2020–present X167 GLS 350 d
  • 2021-present W223 S 350 d


  • 250 kW (340 PS; 335 hp) at 3,600–4,400 rpm 700 Nm (516 lbft) at 1,200–3,200 rpm

Fitted to the...

  • 2017–present W222 S 400 d
  • 2018–present C257 CLS 400 d 4MATIC
  • 2018–present W213 E 400 d
  • 2018-present W463 G400 d
  • 2019–present V167 GLE 400 d
  • 2020–present X167 GLS 400 d
  • 2021-present W223 S 400 d 4MATIC

Tuning the Mercedes OM656 and best OM656 performance parts.

Best OM656 mods

The best OM656 modifications on an engine are obviously the ones that give the best value for money.

We won't be swayed by popular OM656 modifications, they need to be cost effective.

Altering your OM656 cam will make a dramatic difference to the engine bhp. Choosing a higher performance cam profile raises the bhp accordingly.

Fast road camshafts usually push up the bhp and torque throughout the rpm band, you could drop a little low end power but your higher rpm power will be lifted.

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

On a car used daily must carefully try to match your engines power to your preferences.

You will never have found a OM656 Race camshaft is a pleasure to live with when driving in heavy traffic. The low end idle will be very lumpy and irregular, so something you would notice on a track when you drive in the upper third of the rpm band, but on roads this is a serious issue and we've heard from lots of drivers lamenting their decision to add an extreme competition cam profile to their engine.

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

The ECU mapping and injectors and fuel pump also will say much on the torque gains you'll achieve.

Altering valve durations can alter the torque 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:
    Intake manifolds, Remaps/piggy back ECU, drilled & smoothed airbox, Fast road camshaft, Sports exhaust header/manifold, Panel air filters.

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

    The OM656 power trains respond well to mods and thanks to their popularity there are plenty of upgrades and tuning parts about.

    ECU mapping allows a tuner to release the full potential of all the parts you've done to your OM656.

    (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 rely on the parts you've done and the condition of your engine.

    It is the aim to any engine performance tuning project to push air and fuel into your OM656

    Air Intake manifolds flow the air from the air filter and allow it to be drawn into the engine and mixed with fuel.

    The shape and flow rate of the Air Intake manifolds can make a noticeable difference to fuel mixing and power on the OM656.

    I usually find intake manifolds are ripe for aftermarket parts, although some OEM provide well optimised intake manifolds.

    Adding a OM656 larger valve kit, getting 3 or 5 angle valve jobs and porting and head flowing will also increase bhp, and as an added benefit will give you raising the bhp increase on other upgrades.

    OM656 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 OM656

    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.

    If an engine has forced induction modifications are giving better power gains and you'll see that turbo charged engines are built using many forged and stronger components.

    There are weak spots for every engine, with some being very over engineered and some just sufficiently able to handle stock powerSee where you'll find these limits and fit higher quality crank and pistons to utilize the power.

    It's not unheard of drivers spending a loads on turbocharger upgrades on the OM656 only to have the car literally blow up just after it's used on the roads.

    Big upgraded turbochargers tend to experience no power at low rpm, and small turbochargers spool up quickly but won't have the peak end power band gains.

    Thanks to progress the selection of turbochargers is always moving on and we now see variable vane turbochargers, allowing the vane profile is altered according to speed to lower lag and increase top end power.

    Twin scroll turbochargers divert the exhaust flow into two channels and push these at differently angled vanes in the turbocharger. They also increase the scavenging effect of the engine.

    It is not unusual that there's a limitation in the air flow sensor (AFM/MAF/MAP) on the OM656 when considerably 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 bhp gains, although more challenging to install. We have this guide to twinchargers if you want to read more.


    When you boost the bhp and torque you will need to increase to the fuelling.

    More bhp and torque needs more fuel. Don't forget to over specify your flow rate on the injectors.

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

    OM656 Performance Exhausts

    You should look to replace your exhaust if your exhaust is actually creating a restriction in flow.

    On most factory exhausts you'll find the 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 through the engine but do not go too large or you could very well end up with a reduced flow rate. So generally speaking, keep to 1.5 to 2.5 inches as a rule of thumb.

    Common exhaust restrictions can be located the catalyst installed, so adding a higher 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 OM656

    The OM656 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 OM656, 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 OM656 engine please join us in our car forums where you can discuss OM656 tuning options in more detail with our OM656 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 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 OM656 tuning guides which get regular updates and revisions.

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