Modding uprating the Mitsubishi 6B31 engine!

All you need to know about "6B31 Modifications"

6B31 Modifications Guide

How to modify and upgrade the Mitsubishi 6B31

"Comprehensive guide to tuning the Mitsubishi 6B31 engine!"

Popular tuning sites like TorqueCars are always getting messages requesting info on how to improve the 6B31 from people inquiring about getting more power from the 6B31 and wanting to know what are the best tips on 6B31 mods that work. So let us look into Mitsubishi 6B31 upgrades and outline the best upgrades on this great engine and point out some frequent tuning mistakes along the way.

The Mitsubishi 6B31 really good project engines and with the best sports enhancements like a remap, turbo kits and camshafts you will certainly improve your driving enjoyment.

This pages aim is look into 6B31 tuning and show the best upgrades.

When talking about the ultimate parts for your 6B31 engine, we are going to concentrate on the upgrades that give the best power gain for you spend.

6B31 induction kits

Improving air intake on the 6B31

You need fuel and air for an engine to work. If there is little supply of fuel then it will run lean, if there is insufficient air it runs rich sapping power which risks damage to the 6B31. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Pushing fuel and air into each cylinder is vital to any engine upgrade job.

You'll commonly see there's a restriction in the air flow sensor AFM/MAP on the 6B31 when considerably more air is being sucked into the engine.

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

Air Intake manifolds transmit the during the engines suck phase from the filter and allow it to be fed into the engine cylinders with fuel for the squish phase.

Structure and rate of flow of the Intake can make a large change to fuel mixing and power on the 6B31.

Commonly we find the plenum chambers are improved through performance upgrades, although a few OEM provide reasonably good plenum chambers.

Increasing the 6B31 valve size, doing some 6B31 port enlargement and head flowing will also raise bhp, and importantly will raise potential for a better bhp increase on other parts.

6B31 performance cam tips.

Each engine responds better to different cam durations than others.

The ECU mapping and fuelling also will say much on the power gains you'll hit.

A longer valve duration can alter the power 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.

Altering your 6B31 camshaft will make a dramatic difference to the engine power band. Choosing a higher performance camshaft profile raises the power band accordingly.

NB: Fast road cams commonly raise the bhp and torque through the rev band, you may sacrifice a little bottom end torque but your high end rpm power will improve.

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.

In a daily driver you should ideally to optimize your engines power to your typical driving style.

I'd be surprised if you find a 6B31 Motorsport and race cam is a pleasure to live with when driving in heavy traffic.

Stage 1, 2 and 3 mods for the 6B31

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 6B31 parts:

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

Stage 2 6B31 parts:

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

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

Stage 3 6B31 parts:

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

Review your options and then source your modifications and set yourself a power target to avoid expensive mistakes.

A remap allows a tuner to fully realize the full potential of all the parts you've done to your 6B31.

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 done and the condition of your engine.

Turbo modifications on the 6B31

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 6B31.

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 the engine has a turbocharger parts are relatively easy and most turbocharged engines already contain more solid components.

However you will find an engines will have power limits

It is important to find these limits and upgrade to stronger pistons, crank and engine components to cope with the power.

There are many mechanics spending a fortune on turbo upgrades on the 6B31 only to have the 6B31 catastrophically fail on it's first outing after it's first rolling road session.

Big turbochargers will usually suffer no power at low rpm, and low capacity turbochargers spool up more quickly but don't have the high rpm engines power gains.

Thanks to new tech the world of turbo chargers is always increasing and we commonly find variable vane turbo chargers, permitting the vane angle is altered according to speed to lower lag and increase top end torque.

Twin scroll turbo chargers divert the exhaust gases into 2 channels and push these at differently designed vanes in the turbo. They also help the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large torque gains, although harder to install. We have this feature on twinchargers if you want to read more.

Tips about fuel supply on the 6B31

Don't forget to boost the fuel delivery when you are increasing the performance - it makes the car more thirsty. Most tuners we speak with say to over specify your injectors flow rate.

The rule of thumb is to add 20% to the flow rate when fitting an injector, this allows for injector deterioration and gives you some 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 6B31 performance exhaust upgrades

Only look to boost your exhaust system with an upgraded one is if your current exhaust is actually creating a restriction.

On most factory exhausts you should find that your flow rate is still fine 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.

Don't go with the biggest exhaust you can buy this will slow the exhaust rate - the best for power gains are usually between one and a half to two and half inches. Your exhaust design, the bend angles and construction are what have more effect on flow rates than your pipe width to a certain extent. So the exhaust design is a big factor.

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

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

Faults issues and things to look out for on the 6B31

Like most engines an 6B31, 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 6B31, failure to do this will exacerbate engine wear, on a tuned 6B31 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 6B31 why not pop over to the forums at TorqueCars where you can chat about 6B31 tuning options and read about others projects who may be planning to do similar modifications on their 6B31.

We need your help to complete and improve this page, so do give us your feedback in the comments box below.

We want to know your experiences with modifications on your 6B31, it helps us improve our tips and keeps us current so please use the comments box to drop a tip.

If you liked this page please share it with your friends, drop a link to it in your favourite forum or use the bookmarking options to save it to your social media profile.

Check out TorqueCars new YouTube channel, and see their awesome new content...


Please use our forums if you wish to ask a tuning question, and please note we do not sell parts or services, we are just an online magazine.

Help us improve, leave a suggestion or tip

Your Constructive comments on this article