Mercedes OM668 Tuning

"All you need to know about tuning the Mercedes OM668 engine!"

Herein we review and look at OM668 tuning and provide tips on the best upgrades. Mercedes OM668 really good project engines and with a few sensible uprated upgrades like ECU maps, turbo improvements and camshafts you will greatly maximize your driving fun.

History, Power & Specs of the OM668 Engine

OM 668 DE 17 A

44 kW (59 hp) at 3600 160 Nm (118 lbft) at 1500–2400

  • A 160 CDI (1997 - 2001)

OM 668 DE 17 LA red.

55 kW (74 hp) at 3600

160 Nm (118 lbf⋅ft) at 1500–2800

  • A 160 CDI (2001 - 2004)
  • Vaneo CDI

OM 668 DE 17 LA

66 kW (89 hp) at 4200 180 Nm (133 lbft) at 1600–3200

  • A 170 CDI (1997 - 2001)
  • Vaneo 1.7 CDI

OM 668 DE 17 LA

70 kW (94 hp) at 4200 180 Nm (133 lbft) at 1600–3600

  • A 170 CDI (2001 - 2004)

Tuning the Mercedes OM668 and best OM668 performance parts.

Best OM668 parts

The best OM668 upgrades on an engine are in our opinion the ones that give the best power gain for you spend.

We won't be swayed by popular OM668 upgrades, they need to be cost effective.

Significant gains on the OM668 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

Fast road camshafts usually raise the torque across the rev band, you might lose a little bottom end power but top end will be better.

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

In a car driven daily must carefully try to optimize your engines power to your driving style.

I would be surprised if you find a OM668 Competition cam 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.

Different OM668 engines respond better to less aggressive cam durations than others.

The map and fuel pump and injectors also will say much on the bhp gains you'll hit.

A longer valve duration 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:
    Sports exhaust header/manifold, Remaps/piggy back ECU, Fast road camshaft, Intake manifolds, Panel air filters, drilled & smoothed airbox.

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

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

    The OM668 units make great tuning projects and we note that there is a lot of parts and tuning parts out there.

    ECU mapping will help to establish the full potential of all the parts you've done to your OM668.

    (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 usually differs on the parts you've applied and the condition of your engine.

    It is vital to any performance tuning task to push air into your OM668

    Air Intake manifolds take the air during the suck phase from the air cleaner and allow it to be drawn into the engine cylinders with fuel for the squish phase.

    The size of bore and shape and flow characteristics of the Plenum can make a big change to fuel atomisation and engine efficiency on the OM668.

    It's not uncommon that air intake manifolds are in dire need of performance upgrades, although a few car makers provide fairly well optimized air intake manifolds.

    Adding a OM668 larger valve kit, carrying out port matching and head flowing will also lift torque, and importantly will make space for increasing the torque increase on other tuning parts.

    OM668 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 OM668

    The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes significant power gains.

    When the engine is fitted with a turbocharger upgrades are going to make more power and most turbo charged engines are built with harder and stronger components.

    However engines will have power limits.We recommend you find these restrictions and upgrade to better pistons and crank to utilize the power.

    There are many car owners spending a loads of money on turbo upgrades on the OM668 only to see the motor go up in smoke on it's first outing after it's been completed.

    Larger turbochargers commonly experience no power at low rpm, and low capacity turbochargers spool up much more quickly but won't have the peak rpm engines power gains.

    We are pleased that the range of turbos is always evolving and we are seeing variable vane turbos, where the vane profile is altered according to speed to lower lag and increase top end power.

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

    You'll commonly see there's a limitation in the air flow sensor (AFM/MAF/MAP) on the OM668 when a lot more air is being sucked into the engine.

    You'll see that 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 bhp and torque gains, although more difficult to setup. We have this guide to twinchargers if you want to read more.


    You will need to ensure that the engine is not starved of fuel so will have to ramp up the fuelling when you start extending past 20% of a bhp and torque increase.It is important to over specify your flow rate on the injectors.

    The rule of thumb is to add 20% capacity when buying an injector, this takes into account injector deterioration and provides a bit of 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.

    OM668 Performance Exhausts

    You only need to upgrade your exhaust if your current exhaust is actually causing a restriction in flow.

    On most factory exhausts you'll see the flow rate is 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 can help increase the flow of gases through the engine.

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

    Common exhaust restrictions come around the catalyst installed, so adding a freer 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 OM668

    The OM668 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 OM668, 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 OM668 engine please join us in our car forums where you can discuss OM668 tuning options in more detail with our OM668 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 tuning mods 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 OM668 tuning guides which get regular updates and revisions.

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