Tuning the Mitsubishi 4B4

"Comprehensive guide to tuning and performance parts on the Mitsubishi 4B4 engine!"

We are regularly seeing threads about the best 4B4 modifications. So let us look into Mitsubishi 4B4 upgrades and outline the best upgrades on this great engine and point out some frequent tuning mistakes along the way.

The Mitsubishi 4B4 are awesome to work on and with the optimum modified parts like a remap, turbo upgrades and camshafts you will really improve your driving experience.

We shall look at 4B4 tuning and summarise the greatest modifications.

Just because particular modifications are are common on 4B4 it doesn't mean it is good, instead we'll best modifications that will give your 4B4 the biggest power gain return for your cash.

Significant gains on the 4B4 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

NB: Fast road camshafts normally bump the bhp and torque across the rpm range, you may sacrifice a little low end power but the higher rpm power will improve.

Motorsport camshafts, bump the higher 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 one should, ideally, try to match your bhp range to your driving style.

I would be surprised if you have found a 4B4 Race cam is a pleasure to live with when in heavy traffic.

Some 4B4 engines respond better to more or less aggressive camshaft durations check your engine on a rolling road.

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

Extending exhaust or intake durations 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.

4B4 Tuning Stages

Stage 1 4B4 modifications: Intake headers, Fast road camshaft, Panel air filters, Drilled & smoothed airbox, Remaps/piggy back ECU, Sports exhaust manifold.

Stage 2 4B4 modifications: high flow fuel injectors, fuel pump upgrades, Fast road cam, Sports catalyst & performance exhaust, induction kit, Ported and polished head.

Stage 3 4B4 modifications: Twin charging conversions, Internal engine upgrades (head flowing porting/bigger valves), Crank and Piston upgrades to alter compression, Competition cam, Engine balancing & blueprinting, Adding or Upgrading forced induction (turbo/supercharger).

Review your options and then acquire your mods and set yourself a power target to save yourself from expensive mistakes.

Mapping helps fully realize the full potential of all the tuning parts you've done to your 4B4.

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

Forcing air into the 4B4 engine is vital to any performance tuning task.

Intake headers carry the air from the intake filter and allow it to be pulled into the engine and mixed with fuel.

Shape and flow rate of the Plenum can make a large change to fuel atomisation and engine efficiency on the 4B4.

We often see intake manifold are begging for motorsport parts, although some makers provide decently flowing intake manifold.

Adding a 4B4 larger valve kit, doing a bit of port matching and head flowing will also improve torque, and significantly will permit a greater torque increase on other upgrades.

Turbo upgrades for the 4B4

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 4B4

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 has a turbo already fitted modifications are more reliable and most turbo charged engines are built using many forged and stronger components.

However engines will need better parts at higher power limits

See where you'll find these limitations and install better pistons and crank to handle the power.

There are many people spending a lots of money on turbo charger upgrades on the 4B4 only to see the engine block literally blow up just after it's been completed.

Big upgraded turbo units tend to experience low end lag, and smaller turbo units spool up quickly but won't have the top end power band gains.

In recent times the selection of turbos is always moving on and we commonly find variable vane turbos, where the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbos divert the exhaust gases into two channels and feed these at differently profiled vanes in the turbocharger. They also help the scavenging effect of the engine.

It is common that there's a limitation in the air flow sensor (AFM/MAF/MAP) on the 4B4 when loads more air is being pulled into the engine.

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

Adding a supercharger or additional turbo will make large power gains, although harder to configure. We have this article covering twinchargers if you want to read more.

Uprating 4B4 fuel injectors

Don't overlook the need to boost the fuel delivery when you are increasing the bhp - it makes the car more thirsty. Most tuners we speak with say to be generous with your injectors flow rate.

The accepted safe increase is to add 20% when fitting an injector, helps cope with 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.

Best 4B4 performance exhausts

Only look to replace your exhaust if the existing exhaust is creating a flow problem.

On most factory exhausts you'll find the exhaust 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 balance the flow of air through the engine.

But if your exhaust pipe is too large, ie: it's over 2.5 inches bore, you will lose a lot of the flow rate and end up losing power and torque.

Usual exhaust restrictions can be located the catalyst installed, so adding a faster flowing high performance alternative will help avoid this restriction.

Problems and issues to look out for on the 4B4

The 4B4 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the 4B4, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your 4B4 engine please join us in our friendly forum where you can discuss tuning options in more detail with our 4B4 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 to complete and improve this page, so do give us your feedback in the comments box below.

We really like hearing from our readers, and hearing about which mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our 4B4 guides and tips are kept up to date.

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