Tuning guide "M158 Modifications"

How to modify and upgrade the Mercedes M158

"Comprehensive guide to performance tuning the Mercedes M158 engine!"

Forums like the one at TorqueCars are frequently getting emails asking how to improve the M158 from people wanting to know what are the best tips for M158 power upgrades. So let us look into Mercedes M158 modifications and outline the best mods that work on this great engine and point out some frequent tuning mistakes along the way.

Now we will review and look at M158 tuning and report on the ultimate mods that work. Mercedes M158 make awesome project engines and with a few sensible uprated mods like remapping, turbo kits and camshafts you will certainly enhance your driving experience.

When talking about the best parts for your M158 engine, we are going to focus on the parts that give the best value for money.

Improving air intake on the M158

You need fuel and air for an engine to work. If there is not enough fuel then it will run lean, if there is not enough air it runs rich resulting in lost power and potentially damaging the engine. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Pushing air and fuel into each cylinder is the aim to any engine performance tuning job.

You'll commonly see there is a limit in the air flow sensor AFM/MAP on the M158 when loads more air is being pulled 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.

Intake manifolds carry the on the suck phase from the intake filter and allow it to be fed into the engine and mixed with fuel.

The bore size, shape and flow characteristics of the Air Intake manifolds can make a noticeable change to fuel atomisation on the M158.

Commonly we find the intake headers are begging for performance upgrades, although some car makers provide well optimised intake headers.

Big valve conversions on the M158, carrying out port work and head flowing will also increase torque, and more importantly will permit a better torque increase on other mods.

M158 performance cam tips.

Each engine responds better to mild cam durations than others.

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

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.

Significant air intake, and exhaust improvements on the M158 can be made from cam upgrades. Changing the cam profile alters the intake and exhaust durations on the engine and can dramatically change the torque and power output.

NB: Fast road cams usually raise the performance throughout the rpm range, you could sacrifice a little bottom end bhp but the high end rpm power will improve.

Race cams, raise 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 camshaft is not great driving in heavy traffic.

You should ideally optimize your power band to your usage of the car so for a daily driver stick with a mild fast road M158 camshaft

Stage 1, 2 and 3 mods for the M158

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 M158 parts:

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

Stage 2 M158 parts:

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

Stage 3 M158 parts:

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

Remapping will help to establish the full potential of all the modifications you've done to your M158.

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 mileage will vary depending on the modifications you've done and the condition of your engine.

Turbo modifications on the M158

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 M158.

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.

When an engine is turbo charged parts are simpler to install and we find turbo charged engines will have better components.

There are reliable limits for every engine, with some being incredibly solid and some only just able to handle stock power

Research these limitations and fit forged components to survive the power.

We've seen people spending a loads on turbo charger upgrades on the M158 only to experience the M158 catastrophically fail soon after it's been completed.

Big upgraded turbos commonly suffer a bottom end lag, and low capacity turbos spool up more quickly but do not have the top end power band gains.

Over the last 20 years the range of turbos is always improving and we commonly find variable vane turbos, where the vane profile is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbos divert the exhaust gases into a couple of channels and direct these at differently profiled 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 performance gains, although more challenging to install. We have this article covering twinchargers if you want to read more.

Tips about fuel supply on the M158

You will need to ensure that the engine is not starved of fuel so need to increase the fuelling when you start exceeding 20% of a bhp hike. Most tuners we speak with say to be generous with your flow rate on the injectors.

The accepted safe increase is to add 15% when buying an injector, this accounts for injector deterioration and allows some spare capacity should the engine need 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 M158 performance exhaust upgrades

The only time you should look to boost your exhaust system with an upgraded one is if the current exhaust is creating a restriction.

On most factory exhausts you'll find your flow rate is still ok 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.

Sports exhausts will certainly help air flow out of the engine but do not go too wide or you could will reduce the flow rate. Stick to one and a half to two and half inches as a rule of thumb.

Typically exhaust restrictions can be traced to the emissions filters installed, so adding a freer flowing high performance alternative will help avoid this restriction.

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

Faults issues and things to look out for on the M158

Like most engines an M158, 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 M158, failure to do this will exacerbate engine wear, on a tuned M158 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 M158 why not pop over to the forums at TorqueCars where you can chat about M158 tuning options and read about others projects who may be planning to do similar modifications on their M158.

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