Tuning the Mitsubishi 4J1

"Comprehensive guide to tuning the Mitsubishi 4J1 engine!"

We are regularly seeing threads asking about the best 4J1 upgrades. So let us look into Mitsubishi 4J1 modifications and outline the best modifications on this great engine and point out some potential pitfalls along the way.

TorqueCars will review and look at 4J1 tuning and report on the greatest upgrades. Mitsubishi 4J1 make a good tuning project and with the ultimate modified modifications like ECU maps, turbo improvements and camshafts you will improve your driving experience.

Just because particular tuning mods are appear in lots of 4J1 projects it doesn't mean its worth having, so we'll best tuning mods that will give your 4J1 the best power gain for you money.

Significant gains on the 4J1 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the engines power and power output.

NB: Fast road cams tend to push up the performance over the rev band, you may sacrifice a little low down torque but your higher rpm power will be higher.

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

A Motorsport camshaft won't do well if driving in heavy traffic.

You should ideally optimize your bhp range to your preferences so for a road car stick with a shorter duration 4J1 camshaft

Some 4J1 engines respond better to more or less aggressive cam durations so set your engine up on a rolling road.

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

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.

4J1 Tuning Stages

Stage 1 4J1 modifications: Panel air filters, Sports exhaust manifold, Intake headers, Remaps/piggy back ECU, Fast road camshaft, Drilled & smoothed airbox.

Stage 2 4J1 modifications: Ported and polished head, Sports catalyst & performance exhaust, Fast road cam, fuel pump upgrades, induction kit, high flow fuel injectors.

Stage 3 4J1 modifications: Internal engine upgrades (head flowing porting/bigger valves), Twin charging conversions, Competition cam, Crank and Piston upgrades to alter compression, Engine balancing & blueprinting, Adding or Upgrading forced induction (turbo/supercharger).

The 4J1 engine blocks make great tuning projects and we're happy to report there are plenty of modifications and performance parts out there.

ECU flashing should help to fully realize the full potential of all the upgrades you've done to your 4J1.

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

It is vital to any engine performance tuning project to feed fuel and air into your 4J1

Air Intake manifolds take the air during the suck phase from the filter and allow it to be drawn into the engine cylinders.

The shape and flow characteristics of the Air Intake manifolds can make a big effect on to fuel atomisation and engine efficiency on the 4J1.

Most headers are in desperate need of a performance upgrade, although some OEM provide well optimised headers.

Fitting big valve kits, doing some 3 or 5 angle valve jobs and porting and head flowing will also increase torque, & importantly will raise potential for an improved torque increase on other upgrades.

Turbo upgrades for the 4J1

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 4J1

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes superb power gains.

If your motor has forced induction parts are simpler to install and you'll see that turbo engines are made with more solid components.

There are practical limits for every engine, with some being extremely strong and some only able to handle stock power

Research these limitations and install higher quality components to survive the power.

We see many tuners spending a a stack of money on turbo charger upgrades on the 4J1 only to suffer the humiliation of seeing the engine block explode when it's completed.

Big upgraded turbos commonly experience a bottom end lag, and low capacity turbos spool up much more quickly but do not have the high rpm engines power gains.

In the last 10 years the range of turbo units is always moving on and we now see variable vane turbo units, where the vane angle is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbo units divert the exhaust gases into two channels and flow these at differently profiled vanes in the turbo. They also increase the scavenging effect of the engine.

It is not unusual that there is a limitation in the air flow sensor AFM/MAF on the 4J1 when loads more air is being sucked into the engine.

Going up you'll find 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 bhp and torque gains, although more challenging to install. We have this article on twincharging if you want to read more.

Uprating 4J1 fuel injectors

When you lift the power you will need to uprate to the fuel delivery.

More power needs more fuel. Most tuners we speak with say to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% capacity when buying an injector, helps cope with injector deterioration and gives you some 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 4J1 performance exhausts

You only need to to replace your exhaust if your exhaust is actually causing a flow problem.

On most factory exhausts you'll see the flow rate is still 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 can help increase the flow of gases through the engine.

But if your exhaust pipe is too big, ie: over 2.5 inches bore, you will lose much of the exhaust flow rate and end up losing power and torque.

Usual exhaust restrictions are in the emissions filters installed, so adding a faster flowing high performance alternative will help avoid this restriction.

Problems and issues to look out for on the 4J1

The 4J1 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the 4J1, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your 4J1 engine please join us in our friendly forum where you can discuss tuning options in more detail with our 4J1 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 tuning 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 4J1 guides and tips are kept up to date.

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