Mercedes OM646 Tuning

"All you need to know about tuning the Mercedes OM646 engine!"

The engine belongs to the OM (Oel-Motor) family, which stands for oil engine in German. The OM646 engine came in different power variants, offering a range of power outputs depending on the specific model and tuning. Power outputs typically ranged from approximately 90 horsepower (hp) to 204 hp, with different versions available to suit various vehicle types and applications.

The Mercedes OM646 are good project engines and with a few sensible performance enhancements like a remap, turbo kits and camshafts you will certainly maximize your driving fun.

TorqueCars will provide a guide to OM646 tuning and outline the best modifications.

History, Power & Specs of the OM646 Engine

OM646 DE22 LA R

  • 65 kW (88 PS; 87 hp) @ 3,800 rpm 220 Nm (162 lbft) @ 1,400–2,500 rpm
  • 70 kW (95 PS; 94 hp) @ 3,800 rpm 250 Nm (184 lbft) @ 1,400–2,600 rpm
  • 80 kW (109 PS; 107 hp) @ 3,800 rpm 270 Nm (199 lbft) @ 1,600–2,600 rpm
  • 85 kW (116 PS; 114 hp) @ 3,800 rpm 290 Nm (214 lbft) @ 1,600–2,600 rpm
  • 90 kW (122 PS; 121 hp) @ 4,200 rpm 270 Nm (199 lbft) @ 1,400–2,800 rpm

Fitted to the...

  • 2003–2006 W211 E200 CDI
  • 2003–2007 W203 C200 CDI
  • 2003–2010 W639 Vito 109 CDI, 111 CDI, 2.0 CDI
  • 2008–2010 CL203 CLC200 CDI
  • 2003-2009 Chrysler PT Cruiser

OM646 DE22 LA

  • 110 kW (150 PS; 148 hp) @ 3,800–4,200 rpm 330 Nm (243 lbft) @ 1,200–2,400 rpm

Fitted to the...

  • 2002–2006 W211 E220 CDI
  • 2004–2007 W203 C220 CDI
  • 2003–2010 W639 Vito 115 CDI, 2.2 CDI
  • 2005–2010 C209 CLK220 CDI
  • 2006–2009 W906 Sprinter 209-516 CDI
  • 2008–2010 CL203 CLC220 CDI
  • 2010–2013 Vito (Chinese market; known as OM646 980)


  • 100 kW (136 PS; 134 hp) @ 3,800 rpm
  • 270 Nm (199 lbft) @ 1,600–3,000 rpm
  • 340 Nm (251 lbft) @ 2,000 rpm

Fitted to the...

  • 2006–2009 W211 E200 CDI
  • 2007–2009 W204 C200 CDI


125 kW (170 PS; 168 hp) @ 3,800 rpm 400 Nm (295 lbft) @ 2,000 rpm

2006–2009 W211 E220 CDI
2007–2009 W204 C220 CDI

Tuning the Mercedes OM646 and best OM646 performance parts.

Best OM646 modifications

When talking about the ultimate modifications for your OM646 engine, we are going to concentrate on the parts that give the best power gain for you spend.

The camshaft profile plays a big part in the engines power output so camshaft upgrades make quite a large difference. The intake and exhaust durations will alter depending on the provided camshaft profile.

It makes sense to choose an engine tuner familiar with your specific OM646 engine to ensure a smooth power delivery and bump in power throughout the entire RPM range.

Fast road cams commonly boost the power across the rpm range, you may sacrifice a little low end power but your top end will improve but this is not considered a good mod on the OM646. Availability of performance cam profiles is scarce, and the money is better spend on other mods in most cases.

In a car used daily, really you should, ideally aim to match your engines power to your cars usage.

Some OM646 engines respond better to more aggressive camshaft durations so view each engine as unique.

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

Longer 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 OM646

    1. Engine Tunes - engine tuning/remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
    2. 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.
    3. Upgrades to turbochargers - A forced induction upgrade 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 and should be matched with a tune.
    4. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.

OM646 Tuning stages

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

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

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

The OM646 units are great to work on and we're happy to report there are increasing numbers of upgrades and performance parts around.

Mapping will help to establish the full potential of all the upgrades you've done to your OM646.

(In some cases, especially on older engines, the factory ECU is locked and 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.) There are a few decent tuning boxes around, but most will just dump in more fuel and lead to other running issues.

Engine tunes will usually give you around 30% more power on turbocharged vehicles, but your results may vary depending on the upgrades you've carried out and the condition of your engine.

When the OM646 is fitted to a van the engine is typically setup for torque and not peak power, which is a consideration when you think about a retune.

Forcing air into the OM646 engine is the main goal to any performance tuning project but this needs an equivalent amount of fuel.

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

Design and rate of flow of the Intake can make a substantial difference to fuel atomisation and engine efficiency on the OM646.

I usually find intake manifolds are crying out for aftermarket tuning parts and upgrades on most OM646 applications, although some car models have reasonably good intake manifolds.

Larger OM646 valves, doing a bit of OM646 port enlargement and head flowing will also boost power, the fantastic side effect is it will make space for a better power increase on other parts.

OM646 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 OM646

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 is turbocharged, upgrades are going to net you a larger power gain and most turbocharged engines are built using more solid components.

However engines will need better parts at higher power limits.Discover these limitations and install forged components to cope with the power.

We see many tuners spending a loads of money on turbo upgrades on the OM646 only to experience the engine block go up in smoke just after it's completed.

Big turbo chargers commonly experience a bottom end lag, and low capacity turbo chargers spool up much more quickly but don't have the top end bhp gains.

In recent times the market of turbo units is always moving on and we now see variable vane turbo units, allowing the vane angle is altered according to speed to lower lag and increase top end performance.

Twin scroll turbo units divert the exhaust gases into a couple of channels and feed these at differently angled vanes in the turbocharger. They also improve the scavenging effect of the engine.

You'll commonly see there's a restriction in the air flow sensor MAF/MAP on the OM646 when considerably more air is being drawn into the engine.

We see 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 bhp and torque gains, although more difficult to install. We have this feature on twinchargers if you want to read more.


Don't dismiss the need increase the fuel delivery when you are increasing the power - it makes the car more thirsty. Most tuners we speak with say 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 gives a little 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.

OM646 Performance Exhausts

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

On most factory exhausts you should find that the exhaust flow rate is still 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 equal out the flow of gases through the engine.

But if the exhaust pipe is too big, ie: over 2.5 inches bore, you will lose a lot of the flow rate and end up lacking power and torque.

Usual exhaust restrictions can be 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 OM646

The OM646 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.

Potential DPF and EGR Issues: Some users reported issues with the Diesel Particulate Filter (DPF) and Exhaust Gas Recirculation (EGR) systems in certain OM646 engines. These systems can sometimes become clogged or malfunction, leading to reduced performance and potential maintenance costs.

Reliability: Overall, the OM646 engine is regarded as reliable and robust when properly maintained. Regular servicing and adherence to manufacturer recommendations are crucial to ensure its longevity.

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 OM646, 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 OM646 engine please join us in our car forums where you can discuss OM646 tuning options in more detail with our OM646 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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