Tuning guide "M51 Modifications"

How to modify and upgrade the BMW M51

"Comprehensive guide to tuning the BMW M51 engine!"

Today, let's delve into the world of diesel excellence with a focus on the BMW M51 engine – a robust and efficient powerplant that has left its mark in the realm of diesel-powered vehicles.

The M51, introduced in the 1990s, is a six-cylinder, turbocharged diesel engine that powered various BMW models, including the BMW 5 Series and 7 Series. This engine represents a notable chapter in BMW's history, showcasing the brand's commitment to performance and efficiency in the diesel segment.

In terms of specifications, the M51 boasts a 2.5-liter displacement, and it features a single turbocharger for forced induction. This configuration enhances the engine's power output and torque, making it well-suited for delivering a satisfying driving experience, particularly in larger luxury vehicles.

The M51 proudly features an overhead camshaft (OHC) design, contributing to precise control over the valvetrain. This design choice aligns with BMW's tradition of engineering sophistication, ensuring optimal performance and fuel efficiency.

One notable aspect of the M51 is its reputation for providing a balance between power and fuel economy. In an era when diesel engines were gaining prominence for their efficiency, the M51 stood out as a choice for drivers seeking both performance and long-distance driving capabilities.

As we explore the intricacies of the M51, we witness a chapter in BMW's diesel engine legacy where sophistication and performance coalesce. The M51 engine contributes to the brand's dedication to providing diesel powerplants that meet the expectations of luxury vehicle enthusiasts.

Sites like TorqueCars are frequently getting messages requesting information on how to improve the M51 from people inquiring about getting more power from the M51 and wanting to know what are the things tuners recommend when it comes to M51 mods that work. So let us look into BMW M51 upgrades and outline the best upgrades on this great engine and point out some frequent tuning mistakes along the way.

This pages aim is outline options for your M51 tuning and show the greatest upgrades. BMW M51 are popular tuning projects and with carefully picked motorsport parts like remaps, turbo kits and camshafts you will greatly maximise your driving fun.

Just because particular mods are are common on M51 it doesn't mean you should fit it, instead we'll focus on the optimum mods that will give your M51 the best power gain for you spend.

Without us subscribing to the popular mentality of 'if it's shiny and makes more noise it must be good' you seem to get in many tuning magazines and on car forums'.

Improving air intake on the M51

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 not enough air it runs rich resulting in lost power . We'll pick up on fuelling later in this article but for now we shall look at air supply.

So the aim to any engine tuning project to feed more fuel and air into the M51 engine but this has a knock on effect with the air flow sensor.

It is not unusual that there is a limit in the air flow sensor (AFM/MAF/MAP) on the M51 when loads more air is being sucked into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting bhp at a much lower level.

Engines intake headers carry the air during the suck phase from the filter and allow it to be drawn into the engine cylinders.

Shape and flow characteristics of the Intake can make a noticeable improvement to fuel atomisation and engine efficiency on the M51.

Many mass produced engine air intake manifolds are in dire need of a performance upgrade, although a few makers provide reasonably well designed air intake manifolds.

Fitting big valve kits, getting 3 or 5 angle valve jobs and porting and head flowing will also lift power, and more importantly will give you an improved power increase on other tuning mods.

M51 performance cam tips.

Different M51 engines respond better to more or less aggressive camshaft durations so view each engine as unique.

The engine timing and fuelling also have an effect on the power gains you'll achieve.

Altering valve durations can alter the power 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 M51 can be made from cam upgrades. Changing the cam profile alters the intake and exhaust durations on the engine and can dramatically change the engines power and power output.

NB: Fast road cams commonly raise the bhp over the rev band, you might lose a little low end power but your higher rpm power will be better.

Race cams, raise the higher rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

For a car driven daily you must carefully try to match your power band to your typical driving style.

I'd be gobsmaked if you find a M51 Race cam is a pleasure to live with when in heavy traffic.

Stage 1, 2 and 3 mods for the M51

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 M51 parts:

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

Stage 2 M51 parts:

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

Stage 3 M51 parts:

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

ECU flashing will help fully realize the full potential of all the tuning parts you've done to your M51.

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 the end result will depend much on the tuning parts you've applied and the condition of your engine.

Turbo modifications on the M51

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 M51.

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes superb power gains.

When the engine is turbo charged tuning mods are more reliable and we find turbo charged engines are made with more solid components.

There are common areas of failure for every engine, with some being very over engineered and some only just able to handle stock power

Discover these restrictions and install stronger pistons, crank and engine components to survive the power.

There are many people spending a lot of money on turbo charger upgrades on the M51 only to watch the whole thing throw a rod soon after it's first rolling road session.

Larger turbochargers commonly suffer low end lag, and smaller turbochargers spool up more quickly but don't have the top end engines power gains.

Over the last 20 years the market of turbo units is always developing and we commonly find variable vane turbo units, allowing the vane profile 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 flow these at differently profiled vanes in the turbo charger. They also help the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large power gains, although more complex to setup. We have this feature on twinchargers if you want to read more.

Tips about fuel supply on the M51

When you improve the performance you will need to pay attention to to the fuel delivery.

More performance needs more fuel. Experienced mechanics will tell you to be generous with your flow rate on the injectors.

The rule of thumb is to add another 15% when fitting an injector, this takes into account injector deterioration and gives you some 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 M51 performance exhaust upgrades

You may need to uprate your exhaust system with an upgraded one is if the existing exhaust is actually creating a flow problem.

On most factory exhausts you should find that the exhaust flow rate is still fine 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 can help increase the flow of air through the engine.

But if the exhaust is too big, ie: it's over two and a half inches diameter, you will lose much of the flow rate and end up losing power and torque.

Typically exhaust restrictions come around the emissions filters installed, so adding a better flowing sports alternative will help avoid this restriction.

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

Faults issues and things to look out for on the M51

Like most engines an M51, 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 M51, failure to do this will exacerbate engine wear, on a tuned M51 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 M51 why not pop over to the forums at TorqueCars where you can chat about M51 tuning options and read about others projects who may be planning to do similar modifications on their M51.

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