BMW N40 Tuning

"All you need to know about performance tuning the BMW N40 engine!"

TorqueCars will look into N40 tuning and highlight the premier modifications. BMW N40 are popular tuning projects and with the ultimate tuning parts like ECU maps, turbo improvements and camshafts you will enhance your driving opportunities.

History, Power & Specs of the N40 Engine

N40B16

1,596 cc (97 cu in) 85 kW (114 bhp) at 6,100 rpm 150 Nm (111 lbft) at 4,300 rpm

  • 2001-2005 E46 316i
  • 2001-2005 E46 316ci
  • 2001-2005 E46 316ti

Tuning the BMW N40 and best N40 performance parts.

Best N40 modifications

Just because particular tuning parts are popular with N40 owners it doesn't mean its worth having, instead we will focus on the best tuning parts that will give your N40 the biggest power gain return for your cash.

Significant gains on the N40 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.

Fast road camshafts tend to increase the torque through the rpm band, you might lose a little bottom end bhp but the high end rpm power will be lifted.

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

In a road car you need to optimize your torque band to your usage of the car.

You will never find a N40 Race cam is a pleasure to live with when driving around busy urban areas. This is because a competition cam causes a very lumpy idle, and makes the car more prone to stall or jerk along in stop start traffic, sadly though many ignore this and end up ruining a perfectly good car and having to revert back to a fast road, or OEM cam profile.

Each engine responds better to more aggressive cam durations check your engine on a rolling road.

The ECU mapping 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.

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

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

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

The N40 power trains are great to work on and we're happy to report there is a lot of upgrades and performance parts about.

ECU mapping helps to establish the full potential of all the parts you've done to your N40.

(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 NASP engines, but your results often vary depending on the parts you've fitted and the condition of your engine.

It is vital to any car tuning job to get air into your N40

Intake manifold transmit the air from the filter and allow it to be pulled into the engine cylinders.

Structure and rate of flow of the Intake manifold can make a noticeable difference to fuel atomisation on the N40.

Many mass produced engine intake manifold are needing motorsport parts, although some car makers provide decently flowing intake manifold.

Adding a N40 larger valve kit, getting N40 port enlargement and head flowing will also lift bhp and torque, and importantly will raise potential for a greater bhp and torque increase on other upgrades.

N40 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 N40

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes significant power gains.

When your motor has a turbo already fitted parts are giving better power gains and you'll see that turbo engines will have harder and stronger components.

However every engines will need better parts at higher power limits.We recommend you find these restrictions and fit higher quality crank and pistons to handle the power.

We've seen mechanics spending a lots of money on turbocharger upgrades on the N40 only to suffer the humiliation of seeing the engine block go up in smoke just after it's first rolling road session.

Larger capacity turbos often suffer low end lag, and smaller turbos spool up much more quickly but don't have the peak end engines power gains.

We are pleased that the world of turbochargers is always moving on and we are seeing variable vane turbochargers, permitting the vane angle is altered according to speed to lower lag and increase top end torque.

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

It is common that there is a limitation in the air flow sensor AFM/MAP on the N40 when loads more air is being pulled into the engine.

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

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

Fuelling

When you raise the bhp and torque you will need to pay attention to the fuel delivery.

More bhp and torque needs more fuel. It makes sense to over specify your injectors flow rate.

The rule of thumb is to add 20% capacity when fitting an injector, helps cope with injector deterioration and affords 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 turbocharged engines

  • 58 PSI 340cc/min 200hp
  • 58 PSI 511cc/min 300hp

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

N40 Performance Exhausts

You may need to increase your exhaust if the existing exhaust is actually causing a restriction in flow.

On most factory exhausts you should find that the exhaust flow rate is still 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 balance the flow of gases through the engine.

But if your exhaust pipe is too big, 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.

Common exhaust restrictions can be located the catalysts installed, so adding a faster flowing high performance aftermarket one will improve air flow, and rather than doing an illegal decat, will keep the car road legal.

Weak spots, Issues & problem areas on the N40

The N40 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 N40, 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 N40 engine please join us in our car forums where you can discuss N40 tuning options in more detail with our N40 owners. It would also be worth reading our unbiased BMW tuning articles to get insights into each modification and how effective they will be for your car.

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 upgrades work best for you on your car. Which helps us keep our guides and tips up to date helping others with their modified car projects. Your feedback and comments are used to keep this page up to date, and help improve the accuracy of these N40 articles which are continually updated.

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