Modding and performance tuning parts for the Mitsubishi 4J1 engine!

Tuning guide "4J1 Modifications"

How to modify and upgrade the Mitsubishi 4J1

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

Our friends at TorqueCars are always getting messages about how to improve the 4J1 from people inquiring about getting more power from the 4J1 and wanting to know what are the best tips for 4J1 modifications. So let us look into Mitsubishi 4J1 mods and outline the best mods that work on this great engine and point out some common pitfalls along the way.

We shall review and look at 4J1 tuning and point out the greatest upgrades. Mitsubishi 4J1 are popular tuning projects and with a few sensible modified upgrades like remapping, turbo upgrades and camshafts you will improve your driving fun.

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

Without us subscribing to the popular myth of 'if it's shiny and makes more noise it must be good' you seem to get in many tuning magazines and on car forums'.

4J1 induction kits

Improving air intake on the 4J1

You need fuel and air for an engine to work. If there is insufficient fuel then it will run lean, if there is insufficient air it runs rich losing power and potentially damaging the engine. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Pulling more air and fuel into each cylinder is the aim to any engine performance tuning task.

You'll commonly see there's a restriction in the air flow sensor (AFM/MAF/MAP) on the 4J1 when considerably 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 was restricting performance at a much lower level.

The intake plenum carry the air during the suck phase from the filter and allow it to be pulled into the engine and mixed with fuel.

Shape and rate of flow of the Intake can make a large change to fuel mixing and power on the 4J1.

Many mass produced engine intake manifold are improved through an upgrade, although some car makers provide decently flowing intake manifold.

Larger 4J1 valves, doing a bit of port work and head flowing will also raise power, and significantly will raise potential for a greater power increase on other parts.

4J1 performance cam tips.

Each engine responds better to different camshaft durations so view each engine as unique.

The ECU mapping and fuelling also have a large bearing on the torque gains you'll get.

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.

Significant air intake, and exhaust improvements on the 4J1 can be made from camshaft upgrades. Changing the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the power band and power output.

NB: Fast road cams usually raise the bhp throughout the rev band, you could drop a little bottom end torque but high end rpm power will be lifted.

Motorsport and 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.

For a typical daily driver you should ideally to optimize your engines power to your cars usage.

I'd be amazed if you find a 4J1 Motorsport cam is a pleasure to live with when on the daily commute.

Stage 1, 2 and 3 mods for the 4J1

Before we break the best tuning upgrades down into stages of tune, let's list the most effective tuning upgrades for you.

  1. Suspension Upgrades - always improve your cars handling
  2. Brake Upgrades - Even before adding power improve those brakes
  3. Intake - make sure the intake is not restricted, use filters and intake upgrades to improve this
  4. Exhaust - as with 3 ensure there is not restriction in the exhaust, cats are the usual bottleneck
  5. Tunes - remapping, piggyback ECU's and aftermarket ECU's can all make decent gains
  6. Fuelling - when you've increased power you'll need to match this with more fuel
  7. Turbo upgrades - Improving the intake with a large turbo and better flowing intercooler will be the biggest power gain you'll see (but one of the most complex).

This video guide to tuning cars is a great starting point to work from in your project.

Stage 1 4J1 parts:

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

Tuning tips and articles Engine tuning Transmission tuning Care care Intake & exhaust mods Improve handling Forums

Stage 2 4J1 parts:

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

Stage 3 4J1 parts:

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

The 4J1 units respond well to upgrades and we're happy to report there is a growing number of parts and performance parts about.

Remapping allows a tuner to to establish the full potential of all the parts you've done to your 4J1.

You will typically expect to see gains of approximately 20-30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your mileage will vary depending on the parts you've applied and the condition of your engine.

Turbo modifications on the 4J1

To get a turbo working on a NASP engine there is a lot involved, from lowering compression ratio to improved fuel supply and mapping, so we have found a great guide to helpavoid the common pitfalls or end up with an unfinished project because you were not told what you were getting into by doing this on the 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 significant power gains.

If your car is turbocharged, parts are going to make more power and you'll see that turbocharged engines are made using stronger components.

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

Research these restrictions and fit more solid crank and pistons to utilize the power.

There are many tuners spending a a stack of money on turbocharger upgrades on the 4J1 only to suffer the indignity of watching the car throw a rod just after it's been enthusiastically driven.

Larger upgraded turbo units often experience a bottom end lag, and smaller turbo units spool up really quickly but won't have the peak rpm power band gains.

In recent times the choice of turbochargers is always improving and we now see variable vane turbochargers, where the vane angle is altered according to speed to lower lag and increase top end performance.

Twin scroll turbochargers divert the exhaust flow into two channels and direct these at differently designed vanes in the turbocharger. They also improve the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large bhp and torque gains, although more complex to get working. We have this in depth look at twinchargers if you want to read more.

Tips about fuel supply on the 4J1

You will need to ensure that the engine is not starved of fuel so must increase the fuelling when you start extending past 20% of a performance hike. At this point we flag up the need to be generous with your flow rate on the injectors.

As a rule of thumb add 20% when fitting an injector, this takes into account injector deterioration and affords a bit of spare capacity should the engine need more fuel.

Don't forget that different fuel grades will usually require different settings, a high octane fuel will burn more efficiently than lower octane fuel for example. A car will trim fuel supply to keep within the ideal air fuel mix but at the extreme ends you may need to adjust your injector capacity, or the mapping or you'll get flat spots and potential lean or rich fuel issues..

Recommended 4J1 performance exhaust upgrades

You should look to replace your exhaust system with an upgraded one is if your current exhaust is actually creating a flow problem.

On most factory exhausts you'll see your flow rate is still good even on modest power gains, but on a serious tuning project with a big boost in power you will certainly need to get a better flowing exhaust.

Sports exhausts will certainly help air flow out of the engine but do not go too wide or you could will reduce the flow rate. Stick to one and a half to two and half inches for best results.

Typically exhaust restrictions are in the catalyst installed, so adding a better flowing sports alternative will help avoid this restriction.

Catalyst removal (NB:catalysts reduce harmful engine emissions) is illegal in most countries and regions.

Faults issues and things to look out for on the 4J1

Like most engines an 4J1, should have few issues if it gets properly serviced and looked after.

We cannot stress enough the need for oil changes with the correct grade of oil on the 4J1, failure to do this will exacerbate engine wear, on a tuned 4J1 this is more important than ever and close attention should be paid to your maintenance schedule.

If you are interested in learning more or getting impartial tuning advice for your 4J1 why not pop over to the forums at TorqueCars where you can chat about 4J1 tuning options and read about others projects who may be planning to do similar modifications on their 4J1.

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