Tuning the BMW M21D24

"Comprehensive guide to tuning the BMW M21D24 engine!"

We often are getting posts asking about the greatest M21D24 upgrades. So let us look into BMW M21D24 modifications and outline the best upgrades on this great engine and point out some common pitfalls along the way.

The BMW M21D24 offer good returns when tuned and with the ultimate sports upgrades like remaps, turbo improvements and camshafts you will noticeably maximize your driving experience.

Here we detail the best approach to M21D24 tuning and report on the premier mods that work.

Just because particular upgrades are appear in lots of M21D24 projects it doesn't mean you should fit it, so we'll best upgrades that will give your M21D24 the biggest power gain return for your cash.

Significant gains on the M21D24 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the engines power and power output.

NB: Fast road cams normally boost the bhp and torque through the rev band, you may sacrifice a little low down power but your top end will be higher.

Race cams, boost the top end 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 around busy urban areas.

You should ideally match your bhp range to your usage of the car so for a road car stick with a fast road M21D24 camshaft

Each engine responds better to more aggressive camshaft durations than others.

The ECU mapping and fuel pump and injectors also will make differences 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.

M21D24 Tuning Stages

Stage 1 M21D24 modifications: Fast road camshaft, Intake headers, Panel air filters, Remaps/piggy back ECU, Drilled & smoothed airbox, Sports exhaust manifold.

Stage 2 M21D24 modifications: Sports catalyst & performance exhaust, induction kit, Ported and polished head, high flow fuel injectors, fuel pump upgrades, Fast road cam.

Stage 3 M21D24 modifications: Twin charging conversions, Adding or Upgrading forced induction (turbo/supercharger), Internal engine upgrades (head flowing porting/bigger valves), Competition cam, Crank and Piston upgrades to alter compression, Engine balancing & blueprinting.

Carefully think through your options and then buy your parts and set yourself a power target to save yourself from expensive mistakes.

ECU flashing should help to to establish the full potential of all the parts you've done to your M21D24.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but power output often depend much on the parts you've applied and the condition of your engine.

It is the whole point to any engine modification project to force more air into each cylinder

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

The bore size, shape and flow rate of the Intake manifold can make a substantial difference to to fuel atomisation on the M21D24.

It's not uncommon that plenum chambers are begging for motorsport parts, although a few makers provide fairly well optimized plenum chambers.

Adding a M21D24 larger valve kit, doing some M21D24 port enlargement and head flowing will also increase torque, & importantly will give you a greater torque increase on other upgrades.

Turbo upgrades for the M21D24

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 M21D24

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.

If your car is fitted with a turbocharger modifications are going to make more power and you will discover turbocharged engines will have stronger components.

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

It is important to find these limitations and upgrade to forged components to cope with the power.

There are many people spending a fortune on turbo charger upgrades on the M21D24 only to suffer the indignity of watching the engine explode on it's first outing after it's been finished.

Large upgraded turbo units will usually experience no power at low rpm, and little turbo units spool up really quickly but don't have the top end engines power gains.

Thanks to new tech the selection of turbochargers is always improving and we are seeing variable vane turbochargers, allowing the vane angle is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbochargers divert the exhaust flow into 2 channels and flow these at differently designed vanes in the turbocharger. They also increase the scavenging effect of the engine.

It is common that there is a limit in the air flow sensor AFM/MAP on the M21D24 when a lot more air is being pulled into the engine.

Going up you'll find 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 bhp and torque gains, although more complex to install. We have this feature on twinchargers if you want to read more.

Uprating M21D24 fuel injectors

You will need to ensure that the engine is not starved of fuel so should pay attention to the fuelling when you start exceeding 20% of a bhp and torque increase.It makes sense to over specify your injector capacity.

The rule of thumb is to add 20% to the flow rate when specifying an injector, helps cope with injector deterioration and gives a bit of spare capacity should the engine need 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 M21D24 performance exhausts

You may need to increase your exhaust if your exhaust is creating a flow problem.

On most factory exhausts you should find that your 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.

Sports exhausts will certainly help air flow out of the engine but avoid an exhaust that is too large or you may end up will reduce the flow rate. Stick to 1.5 to 2.5 inches as a rule of thumb.

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

Problems and issues to look out for on the M21D24

The M21D24 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the M21D24, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your M21D24 engine please join us in our friendly forum where you can discuss tuning options in more detail with our M21D24 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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We really like hearing from our readers, and hearing about which tuning mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our M21D24 guides and tips are kept up to date.

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