BMW M40 Tuning

"All you need to know about tuning the BMW M40 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.

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

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.

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

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

Stage 3 mods: 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.

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 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.

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 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

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 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

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 will help avoid this restriction.

Weak spots Issues & problem areas on the M40

The M40 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Regular oil changes are vital on the M40, especially when tuned and will help extend the life and reliability of the engine.

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 tuning articles to get a full grasp of the benefits and drawbacks of each modification.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which mods work best for them on each model of car. Comments are used to improve the accuracy of these M40 articles which are continually updated.

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