BMW N42 Tuning

"All you need to know about tuning the BMW N42 engine!"

Let us detail the best approach to N42 tuning and report on the optimum modifications.

BMW N42 make a good tuning project and with carefully chosen sports upgrades like ECU maps, turbo upgrades and camshafts you will noticeably maximize your driving enjoyment.

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History, Power & Specs of the Engine

Produced between 2001-2004 the N42 engine  DOHC valvetrain, VANOS (variable valve timing) Valvetronic (variable valve lift)

The non VANOS N40 engine was based on the N42


  • 114 bhp @5,500 rpm 175 Nm (129 lbft) @3,750 rpm


  • 141 bhp @6,000 rpm 200 Nm (148 lbft) @ 3,750 rpm

Tuning the BMW N42 and best N42 performance parts.

Best N42 tuning mods

When talking about the best greatest for your N42 engine, we are going to focus on the parts that give the best power gain for you money.

Altering your N42 cam will make a dramatic difference to the engine power band. Choosing a higher performance cam profile raises the power band accordingly.

Fast road cams usually raise the power over the rev band, you may lose a little low down torque but your high end rpm power will be lifted.

Motorsport and race cams, raise the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

On a road car you need to match your torque band to your cars usage.

You'll never find a N42 Competition 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.

Different N42 engines respond better to extreme camshaft durations check your engine on a rolling road.

The ecu map and fuel pump and injectors also will say much on the bhp gains you'll hit.

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.

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Best Engine Mods for your car

  1. Mapping - remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.

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

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

The N42 engine blocks respond well to upgrades and we're happy to report there is an increase of mods and tuning parts around.

ECU flashing helps fully realize the full potential of all the upgrades you've fitted to your N42.

(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 NA (naturally aspirated) engines, but your mileage often rely on the upgrades you've fitted and the condition of your engine.

Getting air into the N42 engine is the aim to any tuning project.

Intake manifold carry the air from the air filter and allow it to be drawn into the engine and mixed with fuel.

Structure and rate of flow of the Intake manifold can make a large improvement to fuel atomisation and engine efficiency on the N42.

On popular production engines plenum chambers are crying out for motorsport parts, although a few OEM provide reasonably well designed plenum chambers.

Larger N42 valves, carrying out port work and head flowing will also raise power, and importantly will afford you a greater power increase on other parts.

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 N42

We don't think adding a turbo to the N42 is worthwhile, as it will cost much time and money to setup correctly and there are better ways to spend this money on your BMW.

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.

You'll commonly see there's a limit in the air flow sensor AFM/MAP on the N42 when loads more air is being drawn into the engine.

We see 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 gains, although more challenging to install. We have this feature on twinchargers if you want to read more.


Don't forget to look at the fuel delivery when you are increasing the torque - it makes the car more thirsty. It is important to over specify your flow rate on the injectors.

The rule of thumb is to add 20% when fitting an injector, helps cope with injector deterioration and provides you some 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


You may need to increase your exhaust if the current exhaust is actually creating a flow problem.

On most factory exhausts you'll see your flow rate is 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 can usually air flow from the engine but avoid an exhaust that is too large or you could very well end up with a reduced flow rate. So generally speaking, keep to 1.5 to 2.5 inches as a rule of thumb.

Common exhaust restrictions are traced to the catalyst and filters installed, so adding a freer 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 N42

The N42 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. There are plenty of horror stories around about the N42 but in reality, if looked after it is a very reliable engine.

Overheating has been noted, which is usually down to thermostat issues or silt clogging up the cooling system.

The timing chain will stretch over time, and when you hear a rattle it's time to get it seen to but we'd recommend doing this every 5 years or so anyway.

Regular oil changes are vital on the N42, 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 N42 engine please join us in our friendly forum where you can discuss tuning options in more detail with our N42 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 modifications 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 N42 tuning guides which get regular updates and revisions.

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2 Responses to “N42 Tuning”

  1. sacunha says:

    i have an e46 with the n42b20 engine. I want to have a little more power(changing engine or car isnt an option) what are the best upgrades i can do?

  2. Cristian says:

    Hi there,

    I appreciate a lot the article, wriiten in “easy to understand form”, just in between Profi and normal user level.

    What I would recommend is to add some remarks/advices in respect to oil. Is the factory recommended oil stil valid?

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