Modding tuning and best performance upgrades on the BMW M20 engine!

Tuners tips on "M20 Modifications"

M20 Modifications Guide

How to modify and upgrade the BMW M20

"Comprehensive guide to performance parts and tuning the BMW M20 engine!"

Forums like the one at TorqueCars are frequently getting emails about how to improve the M20 from people inquiring about getting more power from the M20 and wanting to know what are the best M20 mods that work. So let us look into BMW M20 parts and outline the best modifications on this great engine and point out some frequent tuning mistakes along the way.

The BMW M20 are popular engines and with a few sensible performance upgrades like remapping, turbo upgrades and camshafts you will certainly maximize your driving enjoyment.

In this article we review M20 tuning and point out the optimum modifications.

When talking about the top parts for your M20 engine, we are going to focus on the upgrades that give the best power gain for you spend.

M20 induction kits

Improving air intake on the M20

You need air and fuel for an engine to work. If there is not enough fuel then it will run lean, if there is too little air it runs rich losing power which risks damage to the M20. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So the aim to any car tuning job to force more fuel and air into the M20 engine but this has a knock on effect with the air flow sensor.

It is common that there is a limit in the air flow sensor MAP/MAF/AFM on the M20 when a lot more air is being fed into the engine.

We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped performance at a much lower level.

Engine intake manifolds transmit the air during the suck phase from the air filter and allow it to be drawn into the engine cylinders.

Structure and flow rate of the Headers can make a large improvement to fuel atomisation on the M20.

Commonly we find the intake headers are in dire need of aftermarket tuning parts, although a few manufacturers provide fairly well optimized intake headers.

Fitting big valve kits, doing some 3 or 5 angle valve jobs and porting and head flowing will also increase torque, & more importantly will raise potential for a greater torque increase on other parts.

M20 performance cam tips.

Each engine responds better to more aggressive cam durations than others.

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

Longer valve 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.

Altering your M20 camshaft will make a dramatic difference to the engine torque. Choosing a higher performance camshaft profile raises the torque accordingly.

NB: Fast road camshafts tend to push up the torque through the rpm range, you may lose a little low end bhp but your high end rpm power will be higher.

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

A Motorsport and race camshaft won't do well if in heavy traffic.

You should ideally optimize your torque band to your typical driving style so for a car driven daily stick with a fast road M20 camshaft

Stage 1, 2 and 3 mods for the M20

Before we break the best tuning upgrades down into stages of tune, let's list the most effective tuning upgrades for you.

  1. Suspension Upgrades - always improve your cars handling
  2. Brake Upgrades - Even before adding power improve those brakes
  3. Intake - make sure the intake is not restricted, use filters and intake upgrades to improve this
  4. Exhaust - as with 3 ensure there is not restriction in the exhaust, cats are the usual bottleneck
  5. Tunes - remapping, piggyback ECU's and aftermarket ECU's can all make decent gains
  6. Fuelling - when you've increased power you'll need to match this with more fuel
  7. Turbo upgrades - Improving the intake with a large turbo and better flowing intercooler will be the biggest power gain you'll see (but one of the most complex).

This video guide to tuning cars is a great starting point to work from in your project.

Stage 1 M20 parts:

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

Stage 2 M20 parts:

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

Tuning tips and articles Engine tuning Transmission tuning Care care Intake & exhaust mods Improve handling Forums

Stage 3 M20 parts:

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

The M20 power trains are great to work on and thanks to their popularity there is a growing number of upgrades and tuning parts about.

A remap allows a tuner to release the full potential of all the parts you've done to your M20.

You will typically expect to see gains of approximately 20-30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but power output usually vary depending on the parts you've applied and the condition of your engine.

Turbo modifications on the M20

To get a turbo working on a NASP engine there is a lot involved, from lowering compression ratio to improved fuel supply and mapping, so we have found a great guide to helpavoid the common pitfalls or end up with an unfinished project because you were not told what you were getting into by doing this on the M20.

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.

If an engine is fitted with a turbocharger parts are relatively easy and most turbo charged engines are built with stronger components.

However every engines have weakspots

Discover these limits and upgrade to better pistons and crank to survive the power.

We've seen people spending a lot of money on turbo charger upgrades on the M20 only to have the engine explode just after it's been enthusiastically driven.

Large capacity turbos tend to suffer low end lag, and little turbos spool up more quickly but don't have the top end power band gains.

Thanks to new tech the range of turbochargers is always increasing and we are seeing variable vane turbochargers, where the vane angle is altered according to speed to lower lag and increase top end power.

Twin scroll turbochargers divert the exhaust gases into 2 channels and direct these at differently angled vanes in the turbocharger. They also increase the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large torque gains, although more complex to get working. We have this feature on twinchargers if you want to read more.

Tips about fuel supply on the M20

You will need to ensure that the engine is not starved of fuel so should look at the fuelling when you start extending past 20% of a bhp hike. Experienced mechanics will tell you to be generous with your injectors flow rate.

As a rule of thumb add 15% to the flow rate when buying an injector, this accounts for injector deterioration and allows a bit of spare capacity should the engine need more fuel.

Don't forget that different fuel grades will usually require different settings, a high octane fuel will burn more efficiently than lower octane fuel for example. A car will trim fuel supply to keep within the ideal air fuel mix but at the extreme ends you may need to adjust your injector capacity, or the mapping or you'll get flat spots and potential lean or rich fuel issues..

Recommended M20 performance exhaust upgrades

We'd only recommend you look to replace your exhaust system with an upgraded one is if the current exhaust is creating a restriction.

On most factory exhausts you'll find the flow rate is good even on modest power gains, but on a serious tuning project with a big boost in power you will certainly need to get a better flowing exhaust.

Sports exhausts generally help improve air flow out of the engine but do not go too large or you could will reduce the flow rate. Stick to one and a half to two and half inches as a rule of thumb.

The usual suspects causing problems in your exhaust flow rate can be traced to the catalysts installed, so adding a faster flowing sports alternative will help avoid this restriction.

Decats (NB:catalysts reduce harmful engine emissions) is illegal in most countries and regions.

Faults issues and things to look out for on the M20

Like most engines an M20, should have few issues if it gets properly serviced and looked after.

We cannot stress enough the need for oil changes with the correct grade of oil on the M20, failure to do this will exacerbate engine wear, on a tuned M20 this is more important than ever and close attention should be paid to your maintenance schedule.

If you are interested in learning more or getting impartial tuning advice for your M20 why not pop over to the forums at TorqueCars where you can chat about M20 tuning options and read about others projects who may be planning to do similar modifications on their M20.

We need your help to complete and improve this page, so do give us your feedback in the comments box below.

We want to know your experiences with upgrades on your M20, it helps us improve our tips and keeps us current so please use the comments box to drop a tip.

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.

Check out TorqueCars new YouTube channel, and see their awesome new content...


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

You must be logged in to post a comment.