Tuning the Mitsubishi 4B1

"Comprehensive guide to performance parts and tuning the Mitsubishi 4B1 engine!"

We are frequently getting posts about the best tips for 4B1 upgrades. So let us look into Mitsubishi 4B1 upgrades and outline the best modifications on this great engine and point out some potential pitfalls along the way.

Now we will examine 4B1 tuning and point out the greatest modifications. Mitsubishi 4B1 have loads of potential and with the optimum sports parts like ECU maps, turbo upgrades and camshafts you will positively improve your driving experience.

Just because particular tuning parts are popular with 4B1 owners it doesn't mean you should fit it, so we'll ultimate tuning parts that will give your 4B1 the best power gain for you money.

The camshaft profile plays a big part in the engines power output so camshaft upgrades make quite a large difference. The intake & exhaust durations will alter depending on the chosen camshaft profile, so large power band gains are on offer for camshaft upgrades.

NB: Fast road camshafts usually raise the bhp and torque throughout the rpm band, you may sacrifice a little bottom end bhp but top end will be lifted.

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

On a daily driver you need to optimize your engines power to your usage of the car.

I'd be surprised if you have found a 4B1 Race cam is a pleasure to live with when driving around busy urban areas.

Some 4B1 engines respond better to more or less aggressive camshaft durations so set your engine up on a rolling road.

The ECU mapping and injectors and fuel pump also have a large bearing on the power gains you'll achieve.

Longer valve durations 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.

4B1 Tuning Stages

Stage 1 4B1 modifications: Sports exhaust manifold, Intake headers, Drilled & smoothed airbox, Remaps/piggy back ECU, Fast road camshaft, Panel air filters.

Stage 2 4B1 modifications: fuel pump upgrades, induction kit, high flow fuel injectors, Sports catalyst & performance exhaust, Ported and polished head, Fast road cam.

Stage 3 4B1 modifications: Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Twin charging conversions, Crank and Piston upgrades to alter compression, Engine balancing & blueprinting, Internal engine upgrades (head flowing porting/bigger valves).

Carefully think through your options and then buy your parts and set yourself a power target to void expensive mistakes.

Remaps will help unlock the full potential of all the upgrades you've done to your 4B1.

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

It is vital to any engine tuning project to pull more fuel and air into each cylinder

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

Design and rate of flow of the Intake can make a large change to fuel atomisation on the 4B1.

We often see air intake manifolds are crying out for performance upgrades, although a few manufacturers provide well optimised air intake manifolds.

Fitting big valve kits, getting port work and head flowing will also raise power, and more importantly will give you raising the power increase on other upgrades.

Turbo upgrades for the 4B1

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 4B1

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

If a car has a turbo already fitted upgrades are more reliable and you'll see that turbo charged engines use many forged and stronger components.

However engines have weakspots

Discover these limits and install better pistons and crank to survive the power.

We see many tuners spending a loads of money on turbo charger upgrades on the 4B1 only to have the engine catastrophically fail just after it's been enthusiastically driven.

Large capacity turbochargers commonly experience a bottom end lag, and low capacity turbochargers spool up much more quickly but won't have the high rpm engines power gains.

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

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

It is not unusual that there is a limit in the air flow sensor MAF/MAP on the 4B1 when considerably more air is being fed into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped performance at a much lower level.

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

Uprating 4B1 fuel injectors

Don't omit to look at the fuel system when you are increasing the torque - it makes the car more thirsty. It is important to be generous with your injectors flow rate.

As a rule of thumb add 20% capacity when specifying an injector, helps cope with 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 4B1 performance exhausts

Only look to upgrade your exhaust if your exhaust is actually creating a restriction in flow.

On most factory exhausts you'll see your 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 equal out the flow of gases through the engine.

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

Typically exhaust restrictions can be located the catalyst installed, so adding a better flowing race alternative will help avoid this restriction.

Problems and issues to look out for on the 4B1

The 4B1 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the 4B1, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your 4B1 engine please join us in our friendly forum where you can discuss tuning options in more detail with our 4B1 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 parts were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our 4B1 guides and tips are kept up to date.

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