BMW M90 Tuning

"All you need to know about performance parts and tuning the BMW M90 engine!"

Let us review M90 tuning and point out the greatest modifications for your car. BMW M90 offers good returns when tuned and with the optimum performance upgrades like remapping, turbo upgrades and camshafts you will dramatically improve your driving fun.

We sometimes get emailed  for some tips on improving the M90 and which tuning modifications we rate as the ultimate, so we've created this guide that covers our go-to modifications and methods of modifying and tuning on the M90 engine.

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History, Power & Specs of the M90 Engine

This was based on the M88 engine design but with an M30 head.


218 PS (160 kW; 215 hp) at 5,200 rpm 304 Nm (224 lbft) at 4,000 rpm 1978–1982 SOHC

  • 1979-1981 E12 M535i
  • 1978-1982 E24 635CSi
  • 1978-1982 E23 735i

Tuning the BMW M90 and best M90 performance parts.

Best M90 upgrades

The greatest M90 parts on an engine are sensibly the ones that give the best value for money.

We won't be swayed by popular M90 parts, they need to be cost effective.

Altering your M90 cam will make a dramatic difference to the engine torque. Choosing a higher performance cam profile raises the torque accordingly.

Fast road cams usually increase the performance over the rpm band, you may sacrifice a little bottom end power but your higher rpm power will be better.

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

A Motorsport camshaft will just annoy you whilst in heavy traffic.

You should ideally optimize your engines power to your driving style so for a car driven daily stick with a mild fast road M90 camshaft

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

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

A longer valve duration 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 mods for your M90

  1. Forced induction upgrades - forced induction is the most efficient approach to raise the intake air supply, allowing you to use more fuel and make power gains. Typically one of the most expensive mods it does provide the largest gains.
  2. Tunes - A remap ensures the biggest gains compared to cost, replacement ECUs, and Tuning boxes are all alternatives.
  3. Low mass flywheel - a lower weight flywheel will improve the engines rev changes. Not beneficial for all M90 engines.
  4. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.
  5. Intake and Sports Exhausts - Note that on their own these mods won't ADD POWER on most cars, but they can help enhance power after other upgrades by lessening the restriction.
  6. Fast road cams are are often the best upgrade for an engine, but they must be setup by someone who knows what they are doing and you might struggle to find one but there might be a local firm to regrind a stock cam .

M90 Tuning Stages

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

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

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

The M90 power plant make great tuning projects and we're happy to report there are increasing numbers of upgrades and tuning parts around.

Mapping will help unlock the full potential of all the tuning mods you've done to your M90.

(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 results usually rely on the tuning mods you've applied and the condition of your engine.

It is the whole point to any tuning task to pull more air and fuel into your M90

Intake flow the air during the suck phase from the filter and allow it to be pulled into the engine cylinders with fuel for the squish phase.

Shape and rate of flow of the Intake manifold can make a noticeable improvement to fuel mixing and power on the M90.

Most intake manifolds are ripe for a performance upgrade, although a few manufacturers provide well optimised intake manifolds.

Adding a M90 larger valve kit, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also improve bhp, and more importantly will raise potential for increasing the bhp increase on other tuning mods.

M90 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 M90

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

When your car is turbocharged, parts are going to net you a larger power gain and turbo charged engines are made with better components.

There are tuning limits for every engine, with some being very over engineered and some just sufficiently able to handle stock powerWe recommend you find these limitations and fit better quality crank and pistons to handle the power.

We've seen guys spending a lot of money on turbo charger upgrades on the M90 only to have the M90 go up in smoke when it's used on the roads.

Bigger upgraded turbochargers tend to experience a bottom end lag, and little turbochargers spool up really quickly but do not have the peak rpm torque gains.

Thankfully the choice of turbo units is always evolving and we now see variable vane turbo units, allowing the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbo units divert the exhaust flow into a couple of channels and flow these at differently profiled vanes in the turbo charger. They also improve the scavenging effect of the engine.

You'll commonly see there is a restriction in the air flow sensor (AFM/MAF/MAP) on the M90 when loads more air is being sucked into the engine.

We note 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 complex to get working. We have this article covering twinchargers if you want to read more.


When you boost the performance you will need to increase to the fuel delivery.

More performance needs more fuel. Most tuners we speak with say to be generous with your flow rate on the injectors.

The accepted safe increase is to add 20% capacity when buying an injector, this takes into account injector deterioration and affords 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.

M90 Performance Exhausts

You may need to upgrade your exhaust if your exhaust is actually creating a flow problem.

On most factory exhausts you'll see your 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 generally help improve air flow out of 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.

Typically exhaust restrictions can be traced to the catalyst and filters installed, so adding a higher 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 M90

The M90 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 M90, 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 M90 engine please join us in our car forums where you can discuss M90 tuning options in more detail with our M90 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.

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We love hearing about our website visitors projects, especially the mods done and which 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 M90 tuning guides which get regular updates and revisions.

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