Mercedes M256 Tuning

"All you need to know about tuning the Mercedes M256 engine!"

The M256 is one of the most innovative inline 6 engines we've seen in quite a while.

The 48V system was required to run the electric compressor, eliminating turbo lag, and the well setup twin scroll turbo gives a very wide power band.

A starter motor actually helps put electrical power (22hp and 180 lbft) directly into the transmission giving excellent response and fuel economy, with all that regenerative tech rolled into it.

The Mercedes M256 are popular tuning projects and with the ultimate uprated enhancements like remapping, turbo improvements and camshafts you will really maximize your driving fun.

Our aim here is to review and look at M256 tuning and provide tips on the best modifications.

History, Power & Specs of the Engine

M256 E30 DEH LA GR

  • (367 PS; 362 hp) at 5,500–6,100 rpm 500Nm (369lbft) at 1,600–4,000 rpm

M256 E30 DEH LA G

  • (435 PS; 429 hp) at 5,900–6,100 rpm 520Nm (384lbft)at 1,800–5,500 rpm

Tuning the Mercedes M256 and best M256 performance parts.

Best M256 tuning mods

The optimum M256 tuning mods on an engine are obviously the ones that give the best power gain for you spend.

We won't be swayed by popular M256 tuning mods, they need to be cost effective.

The cam profile plays a big part in the engines power output so cam upgrades make quite a large difference. The intake & exhaust durations will alter depending on the chosen cam profile, so large bhp gains are on offer for cam upgrades.

Fast road cams tend to push up the power across the rpm band, you may lose a little low down bhp but top end will be better.

Motorsport and race cams, push up the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Motorsport cam will just annoy you whilst on the daily commute, because the lumpy idle will make the car prone to stall and smooth driving at low rpm becomes impossible. If you are developing a track car this doesn't matter as you are in the high end of your RPM range anyway and that is where you want the power to be.

You should ideally optimize your bhp range to your usage of the car so for a car used daily stick with a mild fast road M256 cam

Each engine responds better to more or less aggressive camshaft durations so view each engine as unique.

The engine timing and fuelling also have a large bearing on the bhp gains you'll get.

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.

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Best Engine Mods for your car

  1. Mapping - 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.

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

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

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

 

The M256 power trains respond well to upgrades and we see that there is an increase of upgrades and tuning parts out there.

 

ECU flashing helps to establish the full potential of all the tuning mods you've done to your M256.

(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 results often differs on the tuning mods you've fitted and the condition of your engine.

Pushing air into the M256 engine is vital to any engine upgrade project.

Intake Manifolds carry or channel the air from the filter and allow it to be sucked into the engine cylinders.

The size of bore and shape and flow characteristics of the Intake manifold can make a big change to fuel atomisation and engine efficiency on the M256.

Most intake manifold are improved through performance upgrades, although a few car makers provide reasonably good intake manifold.

Increasing the M256 valve size, doing a bit of port matching and head flowing will also boost performance, the fantastic side effect is it will allow you to get a better performance increase on other tuning parts.

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 M256

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 your motor is fitted with a turbo tuning parts are relatively easy and most turbocharged engines are made with many forged and stronger components.

There are weak spots for every engine, with some being very over engineered and some only just able to handle stock power

Discover these restrictions and fit higher quality components to handle the power.

There are many tuners spending a lots of money on turbo upgrades on the M256 only to have the motor literally blow up just after it's completed.

Bigger capacity turbo units tend to suffer low end lag, and little turbo units spool up really quickly but won't have the peak rpm bhp gains.

Thankfully the market of turbo chargers is always developing and we are seeing variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end power.

Twin scroll turbo chargers divert the exhaust gases into two channels and push these at differently angled vanes in the turbocharger and this is the setup Mercedes went with on the M256. They also help the scavenging effect of the engine.

It is not unusual that there's a limit in the air flow sensor AFM/MAP on the M256 when considerably 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 limited bhp at a much lower level.

Adding a supercharger or additional turbo will make large torque gains, although more difficult to setup. We have this feature on twinchargers if you want to read more.

Fuelling

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

The accepted safe increase is to add 20% capacity when fitting an injector, which takes into account injector deterioration and affords 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.

Exhaust

Only look to boost your exhaust if the current exhaust is actually causing a flow problem.

On most factory exhausts you'll find the exhaust flow rate is still ok even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Do not go with the biggest exhaust you can buy this will slow the exhaust rate - the best exhausts for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions can be located the catalysts installed, so adding a better flowing performance catalyst removes the restriction. We note that performance cats perform similarly to decats and have the added benefit of keeping your car street legal, as decats or catalyst removal is illegal in most territories for road going cars.

Weak spots, Issues & problem areas on the M256

The M256 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 M256, especially when tuned and will help extend the life and reliability of the engine.

Carbon build up is a potential issue on this engine, but it's too early to tell if it will be a problem.

If you would like to know more, or just get some friendly advice on Tuning your M256 engine please join us in our friendly forum where you can discuss tuning options in more detail with our M256 owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which parts 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 M256 tuning guides which get regular updates and revisions.

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One Response to “M256 Tuning”

  1. Edwin Jr Martinez says:

    I have no idea how I did not run into this article. I been excessive research looking into the market between the e53 and e43 and I’m very inclined to the innovative Inline 6 over the v6 but there is a lot of lack of information on this engine until I came across this page. Not a lot of owners care about what they drive so I can only imagine how many e53 and e43 owners want to tune and maintain the car like I do. On top of that there are few tuners even brabus who dont have a lot of options on tuning for this potential beast. Very grateful for this detailed review on the engine.

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