BMW M20 Tuning

"All you need to know about tuning the BMW M20 engine!"

The BMW M20 engines are a great basis for a tuning project and with carefully picked performance upgrades like ECU maps, turbo kits, and camshafts you will dramatically enhance your driving enjoyment.

Before we begin, we are not going to cynically recommend that you fit an induction kit and full exhaust system, earning ourselves commission in the process, when these mods benefits are dubious, instead we will give an honest appraisal of what we feel are the best mods for your car.

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The popularity of the E30 it was fitted in means there are many fans and enthusiasts and no shortage of experience when it comes to mods for the M20 engine.

TorqueCars provide this guide to M20 tuning and highlight the ultimate upgrades and we welcome your suggestions and feedback, which have already helped to make this a comprehensive article.

The M20 engine production ran from 1977 to 1993 and we see the engine evolving from a Carb fed unit, to K, L and LE jetronic systems, and the more recent Bosch Motronic setup.

With different pistons and crank the engine capacity varied from 2.0 to 2.7 liters.

History, Power & Specs of the M20 Engine

M20B20

90 kW (122 PS; 120 bhp) @6,000 rpm 163 Nm (120 lbft) @4,000 rpm
92 kW (125 PS; 123 bhp) @5,800 rpm 170 Nm (125 lbft) @4,000 rpm
95 kW (129 PS; 127 bhp) @6,000 rpm 174 Nm (128 lbft) @4,000 rpm
95 kW (129 PS; 127 bhp) @6,000 rpm 164 Nm (121 lbft) @4,300 rpm

  • 1976–1981 E12 520/6 (carburettor)
  • 1977–1982 E21 320/6 (carburettor)
  • 1981–1982 E28 520i (K-Jetronic)
  • 1982–1984 E28 520i (L-Jetronic)
  • 1982–1984 E30 320i (L-Jetronic)
  • 1984–1987 E28 520i (LE-Jetronic)
  • 1984–1987 E30 320i (LE-Jetronic)
  • 1986–1987 E28 520i (Motronic)
  • 1987–1992 E30 320i (Motronic)
  • 1988–1990 E34 520i (Motronic)

M20B23

105 kW (143 PS; 141 bhp) @5,300 rpm 190 Nm (140 lbft) @4,500 rpm
102 kW (139 PS; 137 bhp) @5,300 rpm 205 Nm (151 lbft) @4,000 rpm
110 kW (150 PS; 148 bhp) @6,000 rpm 205 Nm (151 lbft)  @4,000 rpm

  • 1977–1982 E21 323i (K-Jetronic)
  • 1982–1984 E30 323i (L-Jetronic)
  • 1984–1987 E30 323i (LE-Jetronic)

M20B25

126 kW (171 PS; 169 bhp) @5,800 rpm 226 Nm (167 lbft) @4,000 rpm
125 kW (170 PS; 168 bhp) @5,800 rpm 226 Nm (167 lbft) @4,300 rpm

  • 1985–1993 E30 325i
  • 1989–1990 E34 525i
  • 1988–1991 Z1

M20B27

92 kW (125 PS; 123 bhp) @4,250 rpm 240 Nm (177 lbft) @3,250 rpm
95 kW (129 PS; 127 bhp) @4,250 rpm 240 Nm (177 lbft) @3,250 rpm

  • 1982–1987 E30 325e
  • 1982–1987 E30 325e
  • 1982–1988 E28 525e (called 528e in North America)
  • 1989–1992 E30 325iS (only available in South Africa)

Tuning the BMW M20 and best M20 performance parts.

Best M20 mods

The best M20 tuning parts on an engine are sensibly the ones that give the best power gain for you spend.

We won't be swayed by popular M20 tuning parts, they need to be cost effective.

Altering your M20 cam will make a dramatic difference to the engine power band. Choosing a higher performance cam profile raises the power band accordingly.

Fast road camshafts usually bump the performance over the rpm band, you may lose a little bottom end bhp but your higher rpm power will be higher.

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

A Race cam won't do well if in heavy traffic.

You should ideally optimize your torque band to your preferences so for a car used daily stick with a mild fast road M20 cam

Some M20 engines respond better to extreme camshaft durations so set your engine up on a rolling road.

The ecu map and fuel pump and injectors also have a large bearing on the torque gains you'll get.

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.

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Best mods for your M20

  1. Fast road Camshafts are significant power adders, but TorqueCars recommend they be setup by someone competent and tracking one down can be a challenge but you might find a local firm to regrind a stock camshaft .
  2. Low mass flywheel - a lower weight flywheel will enhance the engines ability to rev freely. But not always not a great upgrade for all M20 engines.
  3. Air Intake and Performance Exhausts - Please be warned on their own these mods won't ADD TORQUE , but they permit you to enhance power after other mods by lessening the restrictive flow.
  4. Upgrades to turbochargers and superchargers - forced induction is the most dramatic method to increase air supply, this means you are able to combust more fuel and make more power. Typically one of the most expensive modifications you'll see massive gains.
  5. Mapping - A replacement ECU, or inline Tuning boxes are all alternatives that work well on the M20 to support improvements in fuel injection and engine timing, but this is quite a complex mod to do.
  6. Flowing and porting the engine head - for larger gains, you will get better flow and make a more efficient engine if you do this to support your other mods.

M20 Tuning Stages

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

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

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

Plan your options and then buy your mods and set yourself a power target to avoid wasting your time and money.

Remaps will help to establish the full potential of all the modifications you've done to your M20.

Fitting fuel injection to the early carb engines is highly recommended and really transforms the engine, although the carb engines sounded great and had a very distinctive quality that is somewhat lost with the advancement of technology.

It will usually give you around 15% on NA (naturally aspirated) engines, but power output usually differs on the modifications you've fitted and the condition of your engine.

It is the main goal to any engine performance tuning task to pull more air into the M20 engine

Your intake manifold will direct the air from the air cleaner and allow it to be drawn into the engine cylinders with fuel for the squish phase.

The shape and flow characteristics of the Intake manifold can make a large effect on to fuel mixing and power on the M20. Also getting a 3 or 5 angle valve job done will raise your engines low end torque and aid fuel atomisation.

Replacing valves with larger valves and head work are quite expensive mods, but they can lift power in a heavily tuned engine by taking out some of the common bottlenecks. Realistically you'll get more bang for your buck by mapping and looking into forced induction.

On popular production engines manifolds are ripe for performance upgrades, although some car makers provide fairly well optimized headers.

Adding a M20 larger valve kit, doing a bit of port work and head flowing will also improve performance, and significantly will afford you increasing the performance increase on other tuning mods.

M20 Turbo upgrades

NA (naturally aspirated) engines  generally 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 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.

On a good solid engine like the M20 you'll be up against the compression ratio, but we've seen some projects happily running a "low boost" turbo setup and making decent power gains.

When the engine has forced induction tuning parts are going to make more power and turbo engines are made using uprated components.

There are common areas of failure for every engine, with some being over specified and some only able to handle stock power. We recommend you find these restrictions and upgrade to more solid crank and pistons to cope with the power.

Big capacity turbo units will usually experience no power at low rpm, and little turbo units spool up much more quickly but do not have the peak rpm torque gains.

Twin scroll turbo units divert the exhaust flow into 2 channels and flow these at differently angled vanes in the turbocharger. They also help the scavenging effect of the engine.

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

We see 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 torque gains, although more complex to setup. We have this feature on twinchargers if you want to read more.

M20 Fuelling Upgrades

Don't omit your cars need to ramp up the fuelling when you are increasing the bhp - it makes the car more thirsty. More power needs more air and more fuel!

A higher capacity fuel pressure regulator on the early M20 engines provides a much sharper throttle response and provides an easy way to deliver more fuel if your existing setup is running at it's limit. There is not much clearance in the engine bay so adjustable fuel pressure regulators are often mounted remotely via a fuel rail adapter.

Don't forget to over specify your injector capacity.

The rule of thumb is to add 20% when specifying an injector, helps cope with injector deterioration and allows 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.

Ethanol based fuels allow you to use a higher air to fuel ratio, so can be a route to making more power if you get the car setup to work on E85 and tune it for more power.

M20 Performance Exhausts

Only look to upgrade your exhaust if the existing exhaust is creating a flow problem. Generally the M20 exhausts flow well, later cars with a cat see some restriction in the headers, but replacing these will only gain you around 3% more power, although you'll notice this more if you have upped the power and added other mods.

On most factory exhausts you'll see the 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.

Catback systems are only going to provide a different sound, rather than a performance gain, despite what some manufacturers may claim. Interestingly larger exhausts actually flow slower, and this can have a detrimental effect on performance.

Don't go with the biggest exhaust you can find you'll slow the exhaust rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions come around the catalysts installed, so adding a freer flowing performance catalyst removes the restriction. We note that performance cats perform similarly to decats and have the added benefit of keeping your car street legal, as decats or catalyst removal is illegal in most territories for road going cars.

There are some areas and regions where you are not permitted to replace a working catalyst, even with a better flowing, more effective "sports" catalyst.

Weak spots, Issues & problem areas on the M20

The M20 engines are generally reliable and solid units, as long as you follow the manufacturer's 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 M20, 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 M20 engine please join us in our car forums where you can discuss M20 tuning options in more detail with our M20 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.

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 tuning 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 M20 tuning guides which get regular updates and revisions.

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