Tuning the Mercedes OM668

"Comprehensive guide to tuning the Mercedes OM668 engine!"

We are frequently getting emails asking about the best OM668 mods that work. So let us look into Mercedes OM668 upgrades and outline the best modifications on this great engine and point out some problems along the way.

In this article we review OM668 tuning and show the greatest modifications. Mercedes OM668 make awesome project engines and with the best sports tuning mods like a remap, turbo improvements and camshafts you will really maximize your driving fun.

Just because particular parts are are common on OM668 it doesn't mean its worth having, so we'll ultimate parts that will give your OM668 the best value for money to power increase.

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 chosen camshaft profile, so large power band gains are on offer for camshaft upgrades.

NB: Fast road cams tend to push up the bhp throughout the rev band, you may sacrifice a little low down power but your higher rpm power will be lifted.

Competition 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 cam will just annoy you whilst in heavy traffic.

You should ideally optimize your bhp range to your driving style so for a daily driver stick with a mild fast road OM668 cam

Different OM668 engines respond better to different camshaft durations so view each engine as unique.

The ECU mapping and fuel pump and injectors also have an effect on the bhp gains you'll achieve.

Longer valve durations 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.

OM668 Tuning Stages

Stage 1 OM668 modifications: Panel air filters, Remaps/piggy back ECU, Fast road camshaft, Intake headers, Drilled & smoothed airbox, Sports exhaust manifold.

Stage 2 OM668 modifications: induction kit, Fast road cam, Sports catalyst & performance exhaust, Ported and polished head, fuel pump upgrades, high flow fuel injectors.

Stage 3 OM668 modifications: Crank and Piston upgrades to alter compression, Engine balancing & blueprinting, Twin charging conversions, Internal engine upgrades (head flowing porting/bigger valves), Adding or Upgrading forced induction (turbo/supercharger), Competition cam.

Mapping allows a tuner to unlock the full potential of all the tuning mods you've done to your OM668.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your mileage often rely on the tuning mods you've carried out and the condition of your engine.

It is the aim to any engine upgrade job to shove more air and fuel into your OM668

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

The bore size, shape and rate of flow of the Intake manifold can make a substantial change to fuel mixing and power on the OM668.

Most intake manifold are begging for an upgrade, although a few manufacturers provide reasonably well designed intake manifold.

Big valve conversions on the OM668, doing some port matching and head flowing will also improve bhp, and significantly will make space for raising the bhp increase on other parts.

Turbo upgrades for the OM668

NASP 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 major power gains.

When a car is turbo charged parts are relatively easy and turbo charged engines are built with many forged and stronger components.

However engines will have power limits

It is important to find these restrictions and install forged components to survive the power.

It's not unheard of people spending a loads of money on turbo upgrades on the OM668 only to suffer the indignity of watching the motor catastrophically fail on it's first outing after it's used in anger.

Large capacity turbochargers often suffer no power at low rpm, and smaller turbochargers spool up more quickly but do not have the peak end power band gains.

Thankfully the range of turbochargers is always evolving and we are seeing variable vane turbochargers, where the vane profile is altered according to speed to lower lag and increase top end performance.

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

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

We see 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting performance at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more complex to get working. We have this in depth look at twinchargers if you want to read more.

Uprating OM668 fuel injectors

You will need to ensure that the engine is not starved of fuel so should increase the fuelling when you start extending past 20% of a bhp and torque increase.It makes sense to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% when buying an injector, helps cope with injector deterioration and allows 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.

Best OM668 performance exhausts

You only need to to increase your exhaust if your exhaust is actually causing a flow problem.

On most factory exhausts you should find that the exhaust 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 balance the flow of air through the engine.

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

Typically exhaust restrictions are traced to the catalyst installed, so adding a better flowing high performance alternative will help avoid this restriction.

Problems and issues to look out for on the OM668

The OM668 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the OM668, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your OM668 engine please join us in our friendly forum where you can discuss tuning options in more detail with our OM668 owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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This article is flagged for an update, so please pass on specific tips below that I can include. All articles, and content was written by me, Waynne Smith TorqueCars founder. Some outlines are just too general so I appreciate your feedback and suggestions. This entry was filed under Mercedes. You can leave a response below or join our forum to discuss this article and car modification in detail with our members.

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