Mitsubishi 4G3 Tuning

"All you need to know about performance tuning the Mitsubishi 4G3 engine!"

In this article we look at 4G3 tuning and outline the greatest modifications for your car. Mitsubishi 4G3 have loads of potential and with a few sensible motorsport upgrades like ECU maps, turbo kits and camshafts you will substantially increase your driving fun.

History, Power & Specs of the Engine

The 4G3 or Saturn engine is a straight 4 OHC engine.

4G30 1969.12-1971.09 Mitsubishi Galant A I (A51)

  • 4G31  1.5l
    1969-1971 Mitsubishi Galant A II, A III (A52)
    1986-1987 Mitsubishi Mirage
  • 4G32 G32B  4G32T 1.4l
  • 4G33 1.4l
  • 4G35 1.7l
  • 4G36 1.2l
    Mitsubishi Celeste
    Mitsubishi Colt
    Mitsubishi Lancer
  • 4G37 1.8l
    Mitsubishi Chariot/Space Wagon 1983-91
    Mitsubishi Cordia
    Mitsubishi Galant
    Mitsubishi Eclipse 1990-1994
    Mitsubishi Lancer/Lancer Fiore/Mirage


Tuning the Mitsubishi 4G3 and best 4G3 performance parts.

Best 4G3 parts

Just because particular parts are popular with 4G3 owners it doesn't mean you should fit it, we shall ultimate parts that will give your 4G3 the best power gain for you spend.

Altering your 4G3 cam will make a dramatic difference to the engine bhp. Choosing a higher performance cam profile raises the bhp accordingly.

Fast road cams normally raise the bhp over the rev band, you may lose a little bottom end bhp but the high end rpm power will be higher.

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 car used daily you need to optimize your power band to your usage of the car.

I would be surprised if you have ever thought or claimed that a 4G3 Motorsport and race cam is a pleasure to live with when in heavy traffic because low end power will be very lumpy. Competition cams are designed for maximum power at the top end of the RPM range, a place that most daily commutes will not permit!

Different 4G3 engines respond better to extreme cam durations check your engine on a rolling road.

The ECU mapping and fuel pump and injectors also will make differences on the power gains you'll get.

Extending exhaust or intake durations can alter the power 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.

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

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

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

The 4G3 power plant are fantastic to work on and we're finding that there is a lot of mods and performance parts around.

Mapping will help fully realize the full potential of all the modifications you've fitted to your 4G3.

(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 NASP engines, but the outcome will rely on the modifications you've carried out and the condition of your engine.

It is the main goal to any engine modification task to force fuel and air into your 4G3

Headers flow the air from the filter and allow it to be drawn into the engine cylinders.

Design and flow characteristics of the Intake can make a substantial difference to to fuel engine efficiency on the 4G3.

Most headers are needing a performance upgrade, although a few car makers provide reasonably well designed headers.

Adding a 4G3 larger valve kit, doing some 3 or 5 angle valve jobs and porting and head flowing will also increase bhp and torque, & more importantly will give you raising the bhp and torque increase on other upgrades.

Turbo upgrades

NASP 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 4G3

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 the engine is fitted with a turbo tuning mods are relatively easy and most turbo engines are made with stronger components.

However engines have weakspots

Research these limits and install higher quality crank and pistons to utilize the power.

It's not unheard of people spending a fortune on turbo charger upgrades on the 4G3 only to experience the 4G3 go up in smoke soon after it's been enthusiastically driven.

Large capacity turbochargers often experience no power at low rpm, and smaller turbochargers spool up much more quickly but do not have the high rpm torque gains.

Thanks to new tech the world of turbochargers is always evolving and we are seeing variable vane turbochargers, allowing the vane angle is altered according to speed to lower lag and increase top end bhp.

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

It is common that there's a limitation in the air flow sensor MAP/MAF/AFM on the 4G3 when loads 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 sapped power at a much lower level.

Adding a supercharger or additional turbo will make large power gains, although more complex to get working. We have this guide to twinchargers if you want to read more.


Don't dismiss the need raise the fuelling when you are increasing the power - it makes the car more thirsty. We would recommend you to be generous with your injector capacity.

As a rule of thumb add another 20% when fitting an injector, this accounts for injector deterioration and allows 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 turbocharged engines

  • 58 PSI 340cc/min 200hp
  • 58 PSI 511cc/min 300hp

4 Cylinder NASP engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp


You only need to to uprate your exhaust if your exhaust is creating a restriction.

On most factory exhausts you should find that 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.

Do not go with the widest exhaust you can find this will reduce the exhaust flow 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 emissions filters installed, so adding a faster flowing sports alternative is the answer. This keeps the car road legal and will flow much better due to it's higher internal surface area and design, so has the added benefit of keeping your car road legal. The alternative decat should be considered an off road only mod, as removing a catalyst is illegal in most territories and regions for road registered cars..

Weak spots Issues & problem areas on the 4G3

The 4G3 engines are generally reliable and solid 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 4G3, 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 4G3 engine please join us in our friendly forum where you can discuss tuning options in more detail with our 4G3 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 upgrades work best for them on each model of car. Comments are used to improve the accuracy of these 4G3 articles which are continually updated.

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