Tuning the BMW M21D24

"Comprehensive guide to performance parts and tuning the BMW M21D24 engine!"

Here we consider M21D24 tuning and highlight the best modifications for your car. BMW M21D24 great bases for a tuning project and with a few sensible performance upgrades like remaps, turbo upgrades and camshafts you will certainly maximise your driving experience.

The ultimate M21D24 upgrades on an engine are obviously the ones that give the best value for money.

We won't be swayed by popular M21D24 upgrades, they need to be cost effective.

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 torque and power output.

NB: Fast road cams tend to boost the torque throughout the rev range, you may sacrifice a little low down torque but high end rpm power will be higher.

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

A Motorsport and race cam is not great driving in heavy traffic.

You should ideally optimize your engines power to your driving style so for a typical daily driver stick with a fast road M21D24 cam

Some M21D24 engines respond better to more or less aggressive camshaft durations so view each engine as unique.

The engine timing and injectors and fuel pump also will say much on the power gains you'll hit.

Extending exhaust or intake 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.

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

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

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

 

Review your options and then acquire your parts and set yourself a power target to avoid costly mistakes.

 

Mapping allows a tuner to release the full potential of all the upgrades 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 usually differs on the upgrades you've applied and the condition of your engine.

Feeding air and fuel into each cylinder is the whole point to any car tuning task.

The intake plenum transmit the air during the suck phase from the filter and allow it to be pulled into the engine cylinders with fuel for the squish phase.

Design and flow characteristics of the Air Intake manifolds can make a big improvement to fuel engine efficiency on the M21D24.

Commonly we find the air intake manifolds are in dire need of aftermarket parts, although some manufacturers provide fairly well optimized air intake manifolds.

Big valve conversions on the M21D24, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also increase power, and as an added benefit will allow you to get increasing the power increase on other modifications.

Turbo upgrades

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 major power gains.

If the engine is fitted with a turbo upgrades are going to make more power and turbo charged engines are built with uprated components.

There are tuning limits for every engine, with some being very over engineered and some just sufficiently able to handle stock power

See where you'll find these limitations and fit forged components to survive the power.

We've seen tuners spending a a stack of money on turbo upgrades on the M21D24 only to see the M21D24 explode when it's finished.

Large turbo units often experience a bottom end lag, and low capacity turbo units spool up much more quickly but won't have the peak rpm engines power gains.

Thankfully the market of turbo chargers is always improving and we now see variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbo chargers divert the exhaust flow into 2 channels and push these at differently angled vanes in the turbo. They also improve the scavenging effect of the engine.

It is not unusual that there's a restriction in the air flow sensor AFM/MAP on the M21D24 when considerably more air is being drawn into the engine.

We see 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped bhp at a much lower level.

Adding a supercharger or additional turbo will make large performance gains, although more challenging to get working. We have this guide to twinchargers if you want to read more.

Fuelling upgrades and mods

When you improve the bhp and torque you will need to ramp up to the fuel system.

 

More bhp and torque needs more fuel. It is important to be generous with your injectors flow rate.

As a rule of thumb add another 20% when specifying an injector, this accounts for injector deterioration and allows some 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.

Exhaust upgrades and mods

You should look to increase your exhaust if the current exhaust is creating a restriction in flow.

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

 

But if the exhaust pipe is too large, ie: it's over 2.5 inches bore, you will lose a great deal of the flow rate and end up losing power and torque.

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

Weak spots, Issues & common problem areas 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.

We need your help improving this article, so please send us your feedback in the comments box below and pass on any tips, points or facts we have wrong or have not covered.

We really like hearing from our readers, and hearing about which parts 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.

History of the Engine

  • Turbo diesel 114 hp 155 lbft @ 2400 rpm
  • NASP 84 hp 112 lbft @ 2500 rpm

The M21 was fitted to the following cars, and was made in quite large numbers. In it's day it was one of the best and most powerful diesel engines around. The NASP version was released later in countries that had higher vehicle taxation costs.

1983 - 1988 E28 524td
1985 - 1988 E28 524d (naturally aspirated)
1985 - 1993 E30 324d (naturally aspirated)
1985 - 1993 E30 324td
1988 – 1991 E34 524td
1984 - 1985 Continental Mark VII
1984 - 1985 Lincoln Continental

Tuning the BMW M21D24 and best M21D24 performance parts.

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