The Lowdown on "OM646 Modifications"

How to modify and upgrade the Mercedes OM646

"Comprehensive guide to performance tuning the Mercedes OM646 engine!"

Our friends at TorqueCars are frequently seeing threads asking how to improve the OM646 from people wanting to know what are the best OM646 modifications. So let us look into Mercedes OM646 tuning mods and outline the best upgrades on this great engine and point out some potential pitfalls along the way.

The Mercedes OM646 are good project engines and with carefully chosen performance modifications like remaps, turbo kits and camshafts you will noticeably increase your driving opportunities.

This pages aim is examine OM646 tuning and show the best modifications.

When talking about the optimum parts for your OM646 engine, we are going to focus on the upgrades that give the best value for money.

Improving air intake on the OM646

You need air matched to fuel for an engine to work. If there is not enough fuel then it will run lean, if there is a lack of air it runs rich sapping power . We'll pick up on fuelling later in this article but for now we shall look at air supply.

So it's important to any engine performance tuning task to feed more air into each cylinder but this has a knock on effect with the air flow sensor.

It is common that there is a limitation in the air flow sensor (AFM/MAF/MAP) on the OM646 when loads more air is being drawn into the engine.

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

Air Intake manifolds take the air during the suck phase from the intake filter and allow it to be fed into the engine and mixed with fuel.

The shape and flow rate of the Intake headers can make a substantial effect on to fuel atomisation on the OM646.

Many mass produced engine intake manifold are in dire need of aftermarket parts, although a few car makers provide decently flowing intake manifold.

Big valve conversions on the OM646, doing a bit of OM646 port enlargement and head flowing will also boost bhp, and significantly will make space for an improved bhp increase on other tuning mods.

OM646 performance cam tips.

Some OM646 engines respond better to more aggressive camshaft durations check your engine on a rolling road.

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

Altering 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.

Altering your OM646 cam will make a dramatic difference to the engine engines power. Choosing a higher performance cam profile raises the engines power accordingly.

NB: Fast road camshafts normally bump the bhp through the rpm band, you might lose a little low down torque but the high end rpm power will be lifted.

Motorsport camshafts, bump the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Competition cam won't do well if on the daily commute.

You should ideally match your power band to your cars usage so for a typical daily driver stick with a fast road OM646 cam

Stage 1, 2 and 3 mods for the OM646

Before we break the best tuning upgrades down into stages of tune, let's list the most effective tuning upgrades for you.

1. Suspension Upgrades - always improve your cars handling
2. Brake Upgrades - Even before adding power improve those brakes
3. Intake - make sure the intake is not restricted, use filters and intake upgrades to improve this
4. Exhaust - as with 3 ensure there is not restriction in the exhaust, cats are the usual bottleneck
5. Tunes - remapping, piggyback ECU's and aftermarket ECU's can all make decent gains
6. Fuelling - when you've increased power you'll need to match this with more fuel
7. Turbo upgrades - Improving the intake with a large turbo and better flowing intercooler will be the biggest power gain you'll see (but one of the most complex).

This video guide to tuning cars is a great starting point to work from in your project.

Stage 1 OM646 parts:

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

Stage 2 OM646 parts:

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

Stage 3 OM646 parts:

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

A remap will help release the full potential of all the parts you've done to your OM646.

You will typically expect to see gains of approximately 20-30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your results usually depend much on the parts you've done and the condition of your engine.

Turbo modifications on the OM646

To get a turbo working on a NASP engine there is a lot involved, from lowering compression ratio to improved fuel supply and mapping, so we have found a great guide to helpavoid the common pitfalls or end up with an unfinished project because you were not told what you were getting into by doing this on the 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 excellent power gains.

When a car is fitted with a turbo upgrades are going to make more power and you will discover turbo charged engines are made using strengthened components.

However most engines have limits

It is important to find these limits and install forged components to utilize the power.

It's not unheard of drivers spending a lot of money on turbo charger upgrades on the OM646 only to have the whole thing literally blow up soon after it's first rolling road session.

Larger capacity turbo chargers often experience no power at low rpm, and small turbo chargers spool up much more quickly but don't have the peak end engines power gains.

Thankfully the world of turbos is always improving and we now see variable vane turbos, permitting the vane angle is altered according to speed to lower lag and increase top end torque.

Twin scroll turbos divert the exhaust gases into 2 channels and direct these at differently designed vanes in the turbocharger. They also improve the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large bhp and torque gains, although more difficult to install. We have this article on twincharging if you want to read more.

Tips about fuel supply on the OM646

You will need to ensure that the engine is not starved of fuel so will have to look at the fuelling when you start extending past 20% of a bhp hike. Experienced tuners recommend to over specify your injector capacity.

The rule of thumb is to add 15% capacity when fitting an injector, this accounts for injector deterioration and allows a little spare capacity should the engine require more fuel.

Don't forget that different fuel grades will usually require different settings, a high octane fuel will burn more efficiently than lower octane fuel for example. A car will trim fuel supply to keep within the ideal air fuel mix but at the extreme ends you may need to adjust your injector capacity, or the mapping or you'll get flat spots and potential lean or rich fuel issues..

Recommended OM646 performance exhaust upgrades

We'd only recommend you look to uprate your exhaust system with an upgraded one is if the current exhaust is creating a flow problem.

On most factory exhausts you'll see your flow rate is good even on modest power gains, but on a serious tuning project with a big boost in power you will certainly need to get a better flowing exhaust.

Please dont run with the largest exhaust you can find you'll reduce the exhaust flow rate - the best exhausts for power gains are usually between one and a half to two and half inches. Your exhaust design, the bend angles and construction are what have more effect on flow rates than your pipe width to a certain extent. So the exhaust design is a big factor.

Usual exhaust restrictions come around the emissions filters installed, so adding a faster flowing high performance alternative will help avoid this restriction.

Decatting (NB:catalysts reduce harmful engine emissions) is illegal in most countries and regions.

Faults issues and things to look out for on the OM646

Like most engines an OM646, should have few issues if it gets properly serviced and looked after.

We cannot stress enough the need for oil changes with the correct grade of oil on the OM646, failure to do this will exacerbate engine wear, on a tuned OM646 this is more important than ever and close attention should be paid to your maintenance schedule.

If you are interested in learning more or getting impartial tuning advice for your OM646 why not pop over to the forums at TorqueCars where you can chat about OM646 tuning options and read about others projects who may be planning to do similar modifications on their OM646.

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This entry was posted under Makes and Models. Tags: engine, mercedes
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