Tuning the BMW M40

"Comprehensive guide to tuning the BMW M40 engine!"

The BMW M40 are popular tuning projects and with carefully chosen uprated enhancements like remaps, turbo improvements and camshafts you will substantially maximise your driving fun.

This pages aim is outline options for your M40 tuning and show the ultimate modifications.

Just because particular mods are appear in lots of M40 projects it doesn't mean its worth having, we shall concentrate) on the top mods that will give your M40 the biggest power gain return for your cash.

Significant gains on the M40 can be made from cam upgrades. Altering 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 camshafts tend to increase the bhp throughout the rev range, you could sacrifice a little low down power but your top end will be lifted.

Race camshafts, increase the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

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

You should ideally optimize your engines power to your driving style so for a typical daily driver stick with a mild fast road M40 cam

Different M40 engines respond better to different camshaft durations so set your engine up on a rolling road.

The map and fuelling also will make differences on the bhp gains you'll make.

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.

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

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

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

The M40 engines are great to work on and we note that there is an increase of parts and tuning parts about.

Remaps will help unlock the full potential of all the mods you've fitted to your M40.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but the end result usually rely on the mods you've applied and the condition of your engine.

Getting air and fuel into the M40 engine is the whole point to any tuning project.

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

The bore size, shape and rate of flow of the Intake manifold can make a substantial improvement to fuel atomisation on the M40.

We often see intake headers are improved through motorsport parts, although some OEM provide reasonably well designed intake headers.

Larger M40 valves, doing some port work and head flowing will also raise bhp, this will permit an improved bhp increase on other upgrades.

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 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 massive power gains.

When a car is turbo charged tuning parts are simpler to install and you'll see that turbo engines are built using harder and stronger components.

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

Discover these limits and install better quality components to cope with the power.

There are many guys spending a loads of money on turbocharger upgrades on the M40 only to experience the M40 explode when it's been finished.

Big turbo chargers commonly experience low end lag, and low capacity turbo chargers spool up quickly but won't have the top end bhp gains.

We are pleased that the world of turbos is always increasing and we are seeing variable vane turbos, where the vane angle is altered according to speed to lower lag and increase top end performance.

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

It is common that there's a limit in the air flow sensor AFM/MAF on the M40 when considerably more air is being fed into the engine.

Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting bhp and torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although harder to get working. We have this feature on twinchargers if you want to read more.

 

History of the 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.

M40B16

98/101 bhp (105 lbft)

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

M40B18

111/114 bhp (121 lbft)

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

Fuelling upgrades and mods

Don't miss you'll need to raise the fuelling when you are increasing the power - it makes the car more thirsty. We would recommend you to be generous with your injectors flow rate.

As a rule of thumb add 20% to the flow rate when fitting an injector, this 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.

4 Cylinder turbocharged engines

  • 58 PSI 340cc/min 200hp

4 Cylinder NASP 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 upgrades and mods

Only look to boost your exhaust if the current exhaust is creating a flow problem.

On most factory exhausts you'll see the exhaust 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 equal out the flow of gases through the engine.

But if your exhaust is too big, ie: it's over 2.5 inches bore, you will lose much of the exhaust flow rate and end up sapping power and torque.

Usual exhaust restrictions can be traced to the catalysts installed, so adding a freer flowing high performance alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the M40

The M40 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the M40, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your M40 engine please join us in our friendly forum where you can discuss tuning options in more detail with our M40 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 modifications were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our M40 guides and tips are kept up to date.

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