BMW M40 Tuning

"All you need to know about tuning the BMW M40B16 and M40B18 engine!"

Here we review M40 tuning and point out the optimum upgrades. BMW M40 are popular engines and with the right modified parts like remapping, turbo kits and camshafts you will really maximise your driving fun.

The engine was produced between 1987 and 1994 with two engine capacities. It was used in the E30 E34 and E36 models and proved to be quite a popular engine, so as you can imagine we often get asked about the best mods for your M40 project engine.

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History, Power & Specs of the M40B16 and M40B18  Engine

The M40 is a SOHC engine and came in 2 sizes, a 1.6 and 1.8. It was offered in a few states of tune over the years with a power drop in 1991.


98/101 bhp (105 lbft)

  • 1988–1994 E30 316i
  • 1990–1994 E36 316i


111/114 bhp (121 lbft)

  • 1987–1994 E30 318i
  • 1988–1994 E34 518i
  • 1992–1993 E36 318i

Tuning the BMW M40 and best M40 performance parts.

Best M40 parts

The ultimate M40 upgrades on an engine are usually the ones that give the biggest return for your cash.

We won't be swayed by popular M40 upgrades, they need to be cost effective.

Altering your M40 cam will make a dramatic difference to the engine engines power. Choosing a higher performance cam profile raises the engines power accordingly.

Fast road camshafts tend to boost the bhp across the rev band, you might lose a little low end torque but high end rpm power will be lifted.

Motorsport camshafts, 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 will just annoy you whilst driving in heavy traffic.

You should ideally match your engines power to your usage of the car so for a car used daily stick with a fast road M40 cam

Some M40 engines respond better to extreme cam durations check your engine on a rolling road.

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

Longer valve durations can alter the torque 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 M40

  1. Flywheel lightening - a reduced weight flywheel will improve the engines rev changes. But not always suitable for all M40 engines.
  2. Fast road Camshafts are one of the most significant mechanical changes, but they must be setup by someone who knows what they are doing and you might struggle to find one but you might find a local firm to regrind a stock camshaft for you.
  3. Flowing and porting the engine head - for larger gains, you will get better flow and make a more efficient engine if you do this to support your other mods.
  4. Intake Upgrades and Exhaust - NB: on their own these mods won't ADD POWER , but they can help enhance power after other mods by removing the restriction.

M40 Tuning Stages

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

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

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

Plan your options and then buy your tuning mods and set yourself a power target to save yourself from expensive mistakes.

Mapping should help to unlock the full potential of all the parts you've fitted to your M40.

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

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 the end result will vary depending on the parts you've done and the condition of your engine.

It is vital to any tuning job to push air into your M40

Air Intake manifolds transmit the air from the intake filter and allow it to be sucked into the engine cylinders with fuel for the squish phase.

The shape and flow characteristics of the Air Intake manifolds can make a big change to fuel atomisation on the M40.

Most air intake manifolds are needing motorsport parts, although some makers provide decently flowing air intake manifolds.

Increasing the M40 valve size, doing a bit of port matching and head flowing will also lift power, and as an added benefit will allow you to get a greater power increase on other tuning mods.

M40 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 M40

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 a car has forced induction parts are going to net you a larger power gain and you'll see that turbocharged engines are made with more solid components.

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

See where you'll find these restrictions and install more solid crank and pistons to cope with the power.

We've seen drivers spending a loads on turbo charger upgrades on the M40 only to watch the car explode soon after it's used in anger.

Larger capacity turbo chargers often experience a bottom end lag, and low capacity turbo chargers spool up quickly but don't have the peak rpm bhp gains.

We are pleased that the market of turbochargers is always improving and we now see variable vane turbochargers, where the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

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

It is not unusual that there is a limitation in the air flow sensor MAF/MAP on these engines when loads more air is being drawn into the engine.

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

Adding a supercharger or additional turbo will make large performance gains, although more difficult to setup. We have this in depth look at twinchargers if you want to read more.

Fuelling Modifications on the M40

When you raise the torque you will need to increase to the fuelling.

The engines used either a Bosch Motronic 1.3 or 1.7 (E30)

More torque needs more fuel. We would recommend you to over specify your injector capacity.

As a rule of thumb add 20% capacity when fitting an injector, which takes into account injector deterioration and gives a bit of 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 turbocharged engines

  • 58 PSI 340cc/min 200hp

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 Modifications and upgrades on the M40

You should look to upgrade your exhaust if the current exhaust is actually causing a flow problem.

On most factory exhausts you'll find the flow rate is good 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 equal out the flow of gases 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 exhaust flow rate and end up lacking power and torque.

Typically exhaust restrictions can be traced to the filters installed, so adding a higher flowing race alternative such as a sports catalyst pretty much removes this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed, but keeps the car road legal.

Weak spots Issues & problem areas on the M40

The M40 engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen 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.

Regular oil changes are vital on the M40, 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 M40 engine please join us in our friendly forum where you can discuss tuning options in more detail with our tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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One Response to “M40 tuning”

  1. Happy Morodi says:

    hi I have BMW E30 318i M40 Engine I need more power I think I will go with Typical stage 3 but without turbo, The Car still running Smoothly I just need more power

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