BMW N40B16 Tuning

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

The BMW N40 engine is a DOHC (Double Overhead Camshaft) four-cylinder petrol engine that served as a replacement for the 1.6-liter versions of the BMW M43 engine. It was produced between 2001 and 2004 and was primarily available in select countries where tax incentives favored vehicles with smaller displacement engines.

The N40 engine is based on the BMW N42 engine platform, sharing the same crankcase, pistons, and bore size of 84 mm (3.3 inches).

This bore size is a key factor in determining the engine's capacity and characteristics. The N40 engine has a redline, or maximum safe engine speed, of 6,500 revolutions per minute (rpm).

One significant difference between the N40 and the N42 engines is the absence of Valvetronic technology in the N40.

Valvetronic is BMW's variable valve lift system, which is designed to optimize engine performance and efficiency. The N40 engine lacks this feature, which distinguishes it from its counterpart.

Another key difference is a shorter stroke in the N40 engine, measuring 72.0 mm (2.8 inches), which results in a smaller displacement compared to the N42. Stroke length plays a crucial role in determining an engine's displacement, with shorter strokes typically leading to smaller engine capacities. This reduction in stroke size is a notable feature of the N40 engine.

The BMW N40 engine represents a specific response to taxation policies in certain regions, where smaller-displacement engines were incentivized.

While it may not have some of the advanced technologies found in other BMW engines, it served as a suitable powerplant for vehicles in markets where tax considerations influenced engine choices.

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.

A site visitor asked for more information on the N40 and how to tune it up and modify it, so we've put together this web page to take you through what we feel are the main modifications that we find are the greatest tuning modifications you can do to this car.

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

Watch my video overview and tips on BMW Tuning. Be sure to keep up with our latest YouTube content and subscribe.

History, Power & Specs of the Engine

DOHC four-cylinder petrol engine  replaced with the N45

  • N40B16 114 bhp @6,100 rpm 150 Nm (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.

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

Please watch our video which covers the 5 principles of tuning your car. Be sure to keep up with our latest YouTube content and subscribe.

Best mods for your N40

  1. Flowing and porting the Head - Head work will get air flowing into the engine while removing turbulence or restrictions.
  2. Flywheel lightening - a lower weight flywheel will improve the engines rev changes. But not always suitable for all N40 engines.
  3. Intake and Exhaust Upgrades - Please note that on their own these mods won't ADD POWER on most cars, but they can help enhance power after other mods by lessening the restriction.
  4. Forced induction upgrades - forced induction is the most efficient approach to raise the intake air supply, this means you are able to combust more fuel and make higher power. Typically one of the most costly mods it does provide the largest gains.

Flowing and Porting the Head:

Head work, which involves porting and flowing the cylinder head, is a significant performance enhancement for the N40 engine.

The primary goal is to optimize the airflow into the engine while eliminating turbulence and restrictions. This modification plays a pivotal role in improving the engine's breathing, allowing it to make the most of other performance-enhancing modifications.

When combined with other upgrades, it can provide substantial power gains and greater overall efficiency.

Flywheel Lightening:

Reducing the weight of the flywheel is a valuable modification for the N40 engine. A lighter flywheel improves the engine's ability to change revs more quickly, resulting in enhanced throttle response and an overall livelier driving experience.

However, it's important to note that this modification may not be suitable for all N40 engines, as it can impact low-end torque, which should be considered based on your driving preferences.

Intake and Exhaust Upgrades:

Upgrading the intake and exhaust systems is vital for optimizing the N40 engine's performance. While these modifications may not individually add power, they significantly contribute to the engine's potential by reducing restrictions.

A free-flowing air intake and performance exhaust enhance overall engine efficiency and power output. These modifications work synergistically with other upgrades, releasing additional power when combined.

Forced Induction Upgrades:

Forced induction, such as turbocharging or supercharging, represents one of the most efficient methods to increase the intake air supply for the N40 engine.

This enables the engine to burn more fuel and generate higher power levels. While it's typically among the costlier modifications, it offers substantial power gains and can transform the N40 engine's performance.

Forced induction upgrades are particularly effective for those seeking significant power improvements.

N40 Tuning Stages

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

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

Typical stage 3 mods often include: 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.

(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.)

As a general rule, you should expect a 15% boost on NA (naturally aspirated) engines, although the actual percentage depends on the components you've installed and the state of your engine.

Any N40 engine tuning effort should have as its primary goal getting air and fuel into the engine.

Headers move the air from the filter to the engine's cylinders, where it is compressed and accelerated.

There are several ways to increase fuel atomization and engine efficiency by changing the shape and flow rate of the Intake manifolds.

Motorsport manifolds are desperately needed on popular production engines, but some manufacturers do provide rather well tuned headers.

Additionally, increasing the bhp and torque by installing an N40 bigger valve kit, doing 3 or 5 angle valve jobs, and porting and head-flowing the engine would free up room to accommodate additional gains in bhp and torque.

N40 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 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.

N40 Fuelling Mods

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 NA (naturally aspirated) engines

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

N40 Performance Exhaust Upgrades

If your current exhaust is restricting your engine's performance, you may need to upgrade it.

Even with small power improvements, the flow rate on most factory exhausts is still adequate. However, when power levels rise, you'll need a better-flowing exhaust.

There is no doubt that sports exhausts will improve airflow out of the engine, but don't go overboard or you'll choke up the whole thing. For optimal results, stick to a size of 1.5 to 2.5 inches.

Addition of a higher flowing performance catalyst reduces the usual exhaust limitation around the filters fitted. These performance cats, like decats, can keep your car legal on the road and perform similarly to decats in terms of horsepower and torque gains.

Weak spots, Issues & problem areas on the N40

As long as you follow the manufacturer's maintenance schedules and use high-quality oil, the N40 engines are sturdy and dependable. Few issues should arise if they are serviced and maintained on a regular basis.

Indirect injection engines have a greater problem with carbon buildup in the head, especially around the valves, which may reduce power or cause flat spots.

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 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 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 tuning guides which get regular updates and revisions.

Please Check out my YouTube channel, we're regularly adding new content...

PLEASE HELP: I NEED YOUR DONATIONS TO COVER THE COSTS OF RUNNING THIS SITE AND KEEP IT RUNNING. I do not charge you to access this website and it saves most TorqueCars readers $100's each year - but we are NON PROFIT and not even covering our costs. To keep us running PLEASE Donate here

If you liked this page please share it with your friends, drop a link to it in your favourite forum or use the bookmarking options to save it to your social media profile.

Feedback - What do You Think?

Please use our forums if you wish to ask a tuning question, and please note we do not sell parts or services, we are just an online magazine.

Help us improve, leave a suggestion or tip

Your Constructive comments on this article, I really want to improve this article with your help and suggestions.

Please watch this video and subscribe to my YouTube channel.

Member Benefits

Join our forum today and benefit from over 300,000 posts on tuning styling and friendly car banter.

You will also have full access to the modifed car gallery, project car updates and exclusive member only areas.

(All car owners of all ages and from all countries are welcome).

BMW 335i - 2021 COTY

We gave the BMW 335i our coveted car of the year award, read more about this awesome car and see why 335i Tuning Guide

Tips for N54 Tuning

Tips for N55 Tuning
Tips for B58 Tuning

Popular articles

Diesel tuning
ECU remapping
double clutching
Induction Kits
Customize a car
Performance Chips
Modified car insurance
Track day insurance
Diesel Remaps
MPG Calculator
Clearing a DPF
Tuning Stages

Adding A Supercharger

Adding a supercharger

Benefits Performance Injectors

The Benefits of Performance Injectors vs. Stock Parts

Lambo Doors

Lambo style doors suicide doors and gullwing door conversions.

Gullwing Doors

Gullwing Doors & gull wing door conversion kits

Car Buying Tips

Tips and a guide to buying a car

Pro Street

Need for speed pro street

MPG Calculator

MPG calculator UK miles per Gallon – calculate MPG