Tuning the Mitsubishi 4A9

"Comprehensive guide to tuning and performance parts on the Mitsubishi 4A9 engine!"

We are regularly getting posts about the best 4A9 mods that work. So let us look into Mitsubishi 4A9 tuning mods and outline the best mods that work on this great engine and point out some common pitfalls along the way.

This pages aim is review and look at 4A9 tuning and provide tips on the optimum upgrades. Mitsubishi 4A9 offer good returns when tuned and with carefully picked tuning enhancements like remaps, turbo improvements and camshafts you will definitely enhance your driving enjoyment.

Just because particular upgrades are popular with 4A9 owners it doesn't mean you should fit it, so we'll greatest upgrades that will give your 4A9 the biggest power gain return for your cash.

Altering your 4A9 cam will make a dramatic difference to the engine power band. Choosing a higher performance cam profile raises the power band accordingly.

NB: Fast road cams commonly push up the bhp and torque through the rpm range, you may lose a little bottom end torque but top end will improve.

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

On a car used daily must carefully try to optimize your power band to your driving style.

I'd be amazed if you have found a 4A9 Race camshaft is a pleasure to live with when driving in heavy traffic.

Some 4A9 engines respond better to different cam durations check your engine on a rolling road.

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

Altering valve 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.

4A9 Tuning Stages

Stage 1 4A9 modifications: Sports exhaust manifold, Panel air filters, Remaps/piggy back ECU, Intake headers, Fast road camshaft, Drilled & smoothed airbox.

Stage 2 4A9 modifications: Fast road cam, fuel pump upgrades, Ported and polished head, high flow fuel injectors, Sports catalyst & performance exhaust, induction kit.

Stage 3 4A9 modifications: Twin charging conversions, Competition cam, Engine balancing & blueprinting, Crank and Piston upgrades to alter compression, Adding or Upgrading forced induction (turbo/supercharger), Internal engine upgrades (head flowing porting/bigger valves).

The 4A9 power plant are great to work on and we see that there are increasing numbers of parts and performance parts out there.

Remaps should help to fully realize the full potential of all the tuning mods you've done to your 4A9.

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 fitted and the condition of your engine.

Pushing air into each cylinder is the whole point to any engine modification job.

The intake plenum flow the air during the suck phase from the filter and allow it to be drawn into the engine cylinders with fuel for the squish phase.

Structure and flow rate of the Intake headers can make a noticeable change to fuel atomisation on the 4A9.

Commonly we find the intake headers are crying out for performance upgrades, although some manufacturers provide well optimised intake headers.

Increasing the 4A9 valve size, doing a bit of 4A9 port enlargement and head flowing will also increase torque, and importantly will make space for an improved torque increase on other mods.

Turbo upgrades for the 4A9

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 4A9

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.

If your car is turbocharged, tuning mods are giving better power gains and you will discover turbo charged engines already contain harder and stronger components.

There are reliable limits for every engine, with some being very over engineered and some just sufficiently able to handle stock power

Research these limitations and upgrade to better pistons and crank to utilize the power.

There are many mechanics spending a fortune on turbocharger upgrades on the 4A9 only to suffer the indignity of watching the motor literally blow up soon after it's first rolling road session.

Bigger turbo chargers will usually experience low end lag, and little turbo chargers spool up really quickly but won't have the top end power band gains.

Thanks to progress the selection of turbo units is always developing and we commonly find variable vane turbo units, allowing the vane angle is altered according to speed to lower lag and increase top end torque.

Twin scroll turbo units divert the exhaust gases into a couple of channels and push these at differently designed vanes in the turbo charger. They also help the scavenging effect of the engine.

It is not unusual that there is a limitation in the air flow sensor MAP/MAF/AFM on the 4A9 when loads more air is being sucked into the engine.

We see 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped bhp and torque at a much lower level.

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

Uprating 4A9 fuel injectors

You will need to ensure that the engine is not starved of fuel so will have to uprate the fuelling when you start exceeding 20% of a performance increase.We strongly recommend you to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% to the flow rate when specifying an injector, this takes into account injector deterioration and affords a bit of spare capacity should the engine require 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 4A9 performance exhausts

You should look to boost your exhaust if the existing exhaust is actually creating a restriction in flow.

On most factory exhausts you'll find the flow rate is still fine 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 gases through the engine.

But if the exhaust is too big, ie: it's over 2.5 inches bore, you will lose much of the exhaust flow rate and end up sapping power and torque.

Usual exhaust restrictions can be traced to the catalyst and filters installed, so adding a higher flowing performance alternative will help avoid this restriction.

Problems and issues to look out for on the 4A9

The 4A9 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the 4A9, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your 4A9 engine please join us in our friendly forum where you can discuss tuning options in more detail with our 4A9 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 4A9 guides and tips are kept up to date.

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