BMW M43 Tuning

"All you need to know about performance parts and tuning the BMW M43 engine!"

Our aim here is to review M43 tuning and outline the best modifications. BMW M43 provide a fun base for your project and with the best mods like ECU maps, turbo upgrades and camshafts you will substantially increase your driving enjoyment.

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History, Power & Specs of the Engine

The M43 is a SOHC straight 4 block.

  • M43B16 1,596 cc
  • 75 kW (102 PS) at 5500 rpm 150 Nm (111 lbft) at 3900 rpm 1991
    60 kW (82 PS) at 5500 rpm 127 Nm (94 lbft) at 3900 rpm 1995-2000
  • M43B18 1,796 cc
  • 85 kW (115 PS) at 5500 rpm 168 Nm (124 lbft) at 3900 rpm 1993
    74 kW (100 PS) at 5500 rpm 142 Nm (105 lbft) at 3900 rpm 1995-1996
  • M43B19 1,895 cc
  • 87 kW (118 PS) at 5500 rpm 180 Nm (133 lbft) at 3900 rpm 1998
    77 kW (105 PS)  at 5300 rpm 165 Nm (122 lbft)  at 2500 rpm 1999

Tuning the BMW M43 and best M43 performance parts.

Best M43 tuning parts

When talking about the best greatest for your M43 engine, we are going to concentrate on the tuning mods that give the biggest return for your cash.

It is fair to say the M43 is not a performance engine, and was built and designed for reliability, however as with all engines there are ways to increase the power, although this is not always cost effective, we will look at the options and leave it up to you to ascertain whether it is worth persuing or not.

Altering your M43 camshaft will make a dramatic difference to the engine engines power. Choosing a higher performance camshaft profile raises the engines power accordingly.

Fast road camshafts normally bump the power across the rpm band, you may sacrifice a little low down power but your high end rpm power will be higher. Sourcing a suitable CAM can be a challenge in some regions, so if this is the case then your best option might be to have a cam regrind to a more aggressive profile.

Competition camshafts, bump the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers, so DO NOT GO TO THE EXTREMES.

A Race cam won't do well if in heavy traffic.

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 M43 cam

Some M43 engines respond better to more or less aggressive cam durations check your engine on a rolling road.

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

Extending exhaust or intake 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 mods for your M43

  1. Lighter flywheels - a reduced weight flywheel will noticeably improve the engines ability to rev freely. But not always recommended for all M43 engines.
  2. Fast road cams are one of the most significant mechanical changes, but TorqueCars recommend they be setup by someone who knows what they are doing and they are not always easy to source but there might be a local firm to regrind a stock camshaft .
  3. Upgrades to turbochargers and superchargers - Adding a turbocharger is the most significant way to raise the intake air supply, ensuring you are able to utilize more fuel and make more power. Although one of the most costly upgrades you'll see massive gains.
  4. Air Intake and high flowing exhausts - NB: on their own these mods will NOT ADD TORQUE for most setups, but they permit you to lift power after other modifications by losing a restriction.
  5. Remaps - A tune/remap ensures the most advantage in terms of cost, replacement ECUs, and inline Tuning boxes are all alternatives.
  6. Internal engine mods - crank, pistons, conrods & compression ratio including balancing and blueprinting

M43 Tuning Stages

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

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

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

The M43 units make great tuning projects and thankfully there is a lot of modifications and tuning parts out there.

ECU mapping allows a tuner to establish the full potential of all the tuning parts you've fitted to your M43.

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 figures achieved may rely on the tuning parts you've fitted and the condition of your engine. We've seen typical power gains, on a stock M43 in the region of 13hp, so not a massive hike, but this will improve if you do other mods as well.

Forcing more fuel and air into your M43 is the aim to any tuning project.

Intake manifold flow the air from the filter and allow it to be sucked into the engine cylinders with fuel for the squish phase. Gas flowing and porting the head will set the car up to handle more power, but on it's own this mod is unlikely to make any dramatic gains for you.

Stroker kits are a great way to increase horsepower, they also allow the option of fitting stronger components and reducing the compression ratio, to allow forced induction upgrades.

The shape and flow characteristics of the Intake can make a noticeable effect on to fuel atomisation and engine efficiency on the M43.

Many mass produced engine intake manifold are ripe for aftermarket tuning parts, although a few OEM provide fairly well optimized intake manifold.

Fitting big valve kits, doing some port work and head flowing will also increase torque, and as an added benefit will give you a better torque increase on other modifications.

M43 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 M43 but you'll need to lower the compression ratio to around 8:5 for this to work.

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.

There are many guys spending a lots of money on turbo charger upgrades on the M43 only to have the M43 literally blow up just after it's first rolling road session. Key things to focus on is lowering the compression ratio (or running low boost), fuelling upgrades and remapping.

Larger capacity turbos often experience a bottom end lag, and little turbos spool up really quickly but don't have the peak rpm bhp gains. The smaller turbos are better suited to the M43 engine.

In recent times the range of turbo chargers is always increasing and we now see variable vane turbo chargers, allowing the vane angle is altered according to speed to lower lag and increase top end performance.

Twin scroll turbo chargers divert the exhaust gases into a couple of channels and direct these at differently angled vanes in the turbo. They also boost the scavenging effect of the engine, sadly we've not found any kits for the M43 yet, but let us know in the comments if you are aware of one, there are many people interested in adding a twin scroll turbo kit.

It is common that there is a restriction in the air flow sensor AFM/MAP on the when loads 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 was restricting performance at a much lower level.

Adding a supercharger or additional turbo will make large torque gains, although more complex to configure. We have this article covering twinchargers if you want to read more.

Fuelling upgrades on the M43

When you raise the bhp you will need to pay attention to the fuelling.

More bhp needs more fuel, this is a simple fact of tuning the M43, and you need to match the fuel and air ratios. Don't forget to be generous with your flow rate on the injectors, overspecifying them is an enshrined principle in tuning cars.

The accepted safe increase is to add another 20% when specifying an injector, this accounts for injector deterioration and allows you some 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.

All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58psi of fuel pressure at idle.

4 Cylinder NA (naturally aspirated) engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp

4 Cylinder supercharged engines

  • 58 PSI 312cc/min 200hp
  • 58 PSI 468cc/min 300hp

Exhaust dowpipes and catback for the M43

You may need to increase your exhaust if your exhaust is actually causing a restriction in flow. Bear in mind the stock exhaust flows really well, so you shouldn't hit a restriction unless you've done some major power upgrades.

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 can usually air flow out of the engine but avoid an exhaust that is too big or you could very well end up with a reduced flow rate. So generally speaking, keep to 1.5 to 2.5 inches as a rule of thumb.

Common exhaust restrictions can be traced to 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 M43

These engines generally prove to be reliable and solid 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.

The DISA valve can fail, which causes rough running, noise.

Oil leaks seem to be a frequent complaing on the M43, especially around the head of the engine, thankfully this is usually down to a gasket issue, so is easily rectified.

Regular oil changes are vital on the M43, especially when tuned and will help extend the life and reliability of the engine.

If you would like to know more, or just get some friendly advice on Tuning your M43 engine please join us in our friendly forum where you can discuss M43 tuning options in more detail with our 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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2 Responses to “M43 tuning”

  1. Phil nawa says:

    My bmw m43 engine e46 has an extensive overheating problem have tried replacing the radiator,water pump,radiator hoses,even did both skimming of the engine block and cylinder head and thermostat just a month apart the overheating prproblem is back again. What could be the problem

  2. TorqueCars says:

    Is the fan cutting in? Bubbles in the water pump circuit are often the cause of overheating, it can be a real pain to eliminate them all. Running the heater on full and tapping the coolant pipes will help move them bubbles around so you can vent them.

    If the fan is not cutting in, it could be the clutch, wiring or a blown fuse?

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