Tuning the Mitsubishi 4G3

"Comprehensive guide to tuning the Mitsubishi 4G3 engine!"

The Mitsubishi 4G3 great bases for a tuning project and with carefully chosen sports tuning mods like ECU maps, turbo improvements and camshafts you will enhance your driving fun.

TorqueCars will review 4G3 tuning and summarise the greatest modifications for your car.

Just because particular modifications are popular with 4G3 owners it doesn't mean its worth having, instead we will highlight what we would class as the best modifications that will give your 4G3 the best value for money to power increase.

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

NB: Fast road cams tend to boost the bhp and torque over the rpm band, you may sacrifice a little low down bhp but the top end will improve.

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

A Motorsport and race cam is not great driving around busy urban areas.

You should ideally optimize your power band to your typical driving style so for a daily driver stick with a shorter duration 4G3 cam

Different 4G3 engines respond better to less aggressive cam durations so set your engine up on a rolling road.

The map and fuel pump and injectors also have an effect on the bhp gains you'll make.

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.

Stage 1 mods: Fast road camshaft, Intake headers, Sports exhaust manifold, Remaps/piggy back ECU, Panel air filters, Drilled & smoothed airbox.

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

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

The 4G3 units respond well to upgrades and we're finding that there is a growing number of upgrades and performance parts about.

Remaps should help to fully realize the full potential of all the tuning mods you've fitted to your 4G3.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your results usually vary depending on the tuning mods you've applied and the condition of your engine.

Pulling more air into the 4G3 engine is the aim to any engine performance tuning project.

Headers take the air during the suck phase from the intake filter and allow it to be fed into the engine and mixed with fuel.

The size of bore and shape and rate of flow of the Headers can make a substantial difference to to fuel delivery on the 4G3.

Commonly we find the intake manifold are ripe for aftermarket parts, although some makers provide decently flowing intake manifold.

Adding a 4G3 larger valve kit, getting 4G3 port enlargement and head flowing will also boost bhp and torque, and significantly will give you an improved 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 major power gains.

When a car is fitted with a turbocharger upgrades are going to net you a larger power gain and most turbo engines already contain many forged and stronger components.

However you will find an engines will need better parts at higher power limits

Research these limits and upgrade to stronger pistons, crank and engine components to utilize the power.

We've seen guys spending a lot of money on turbo upgrades on the 4G3 only to experience the car literally blow up when it's been enthusiastically driven.

Large upgraded turbo chargers commonly experience a bottom end lag, and smaller turbo chargers spool up much more quickly but won't have the top end power band gains.

In recent times the world 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 bhp.

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

It is common that there's a limitation in the air flow sensor AFM/MAP on the 4G3 when a lot 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 limited torque at a much lower level.

Adding a supercharger or additional turbo will make large torque gains, although more complex to install. We have this article on twincharging if you want to read more.

Fuelling upgrades and mods

You will need to ensure that the engine is not starved of fuel so will have to uprate the fuelling when you start extending past 20% of a bhp and torque increase.Most tuners we speak with say to be generous with your injector capacity.

As a rule of thumb add 20% capacity when fitting an injector, this takes into account injector deterioration and affords 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.

Exhaust upgrades and mods

You only need to to improve your exhaust if the existing exhaust is creating a restriction.

On most factory exhausts you'll find the 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 through the engine but avoid an exhaust that is too big or you could will reduce the flow rate. Stick to 1.5 to 2.5 inches as a rule of thumb.

Common exhaust restrictions can be located the emissions filters installed, so adding a freer flowing sports alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the 4G3

The 4G3 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the 4G3, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

History 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


For more information 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.

We need your help improving this article, so please send us your feedback in the comments box below and pass on any tips, points or facts we have wrong or have not covered.

We really like hearing from our readers, and hearing about which upgrades were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our 4G3 guides and tips are kept up to date.

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