BMW N40B16 Tuning

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

The BMW N40 are popular tuning projects and with the right sports mods like remapping, turbo kits and camshafts you will really increase your driving fun.

This pages aim is review N40 tuning and highlight the optimum modifications for your car.

History of the Engine

DOHC four-cylinder petrol engine  replaced with the N45

  • N40B16 114 bhp @6,100 rpm 150 N⋅m (111 lbft) @4,300 rpm

Tuning the BMW N40 and best N40 performance parts.

Best N40 upgrades

When talking about the best best for your N40 engine, we are going to concentrate on the parts that give the biggest return for your cash.

Altering your N40 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 raise the bhp and torque over the rpm band, you could sacrifice a little low down power but top end will improve.

Motorsport camshafts, raise the top end 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 engines power to your driving style.

I'd be shocked if you find a N40 Race cam is a pleasure to live with when in heavy traffic.

Some N40 engines respond better to extreme cam durations so view each engine as unique.

The engine timing and fuelling also will make differences on the torque gains you'll achieve.

A longer valve duration 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: Sports exhaust manifold, Drilled & smoothed airbox, Intake headers, Panel air filters, Fast road camshaft, Remaps/piggy back ECU.

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

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

The N40 engine blocks make great tuning projects and thanks to their popularity there are increasing numbers of parts and performance parts about.

Remaps allows a tuner to fully realize the full potential of all the tuning parts you've fitted to your N40.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but figures achieved usually rely on the tuning parts you've fitted and the condition of your engine.

Getting air and fuel into the N40 engine is the aim to any tuning project.

Headers flow the air from the filter and allow it to be pulled into the engine cylinders.

The shape and flow rate of the Intake headers can make a substantial improvement to fuel atomisation and engine efficiency on the N40.

On popular production engines headers are in dire need of motorsport parts, although some makers provide fairly well optimized headers.

Adding a N40 larger valve kit, doing some 3 or 5 angle valve jobs and porting and head flowing will also lift bhp and torque, & more importantly will make space for an improved bhp and torque increase on other parts.

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

It is not unusual that there's a limitation in the air flow sensor (AFM/MAF/MAP) on the N40 when a lot more air is being fed into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting bhp 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 guide to twinchargers if you want to read more.


Don't miss you'll need to boost the fuel delivery when you are increasing the torque - it makes the car more thirsty. It makes sense to be generous with your injectors flow rate.

The accepted safe increase is to add 20% capacity when fitting an injector, this takes into account injector deterioration and gives a bit of spare capacity should the engine need 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 NASP engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp
  • 58 PSI 568cc/min 400hp
  • 58 PSI 853cc/min 600hp


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

On most factory exhausts you'll see the 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 will certainly help air flow out of the engine but do not go too large or you may end up will reduce the flow rate. Stick to 1.5 to 2.5 inches for best results.

Usual exhaust restrictions come around the filters installed, so adding a better flowing performance alternative will help avoid this restriction.

Weak spots, Issues & problem areas on the N40

The N40 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Regular oil changes are vital on the N40, especially when tuned and will help extend the life and reliability of the engine.

For more information on Tuning your N40 engine please join us in our friendly forum where you can discuss tuning options in more detail with our N40 owners. It would also be worth reading our unbiased 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 parts work best for them on each model of car. Comments are used to improve the accuracy of these N40 articles which are continually updated.

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