Mitsubishi 4B1 Tuning

"All you need to know about performance parts and tuning the Mitsubishi 4B1 engine!"

The Mitsubishi 4B1 are awesome to work on and with carefully picked uprated modifications like remaps, turbo improvements and camshafts you will dramatically enhance your driving pleasure.

Here we review and look at 4B1 tuning and show the best mods that work.

History, Power & Specs of the 4B1 Engine


103–105 kW (140–143 PS; 138–141 bhp) at 6000 rpm


110–116 kW (150–158 PS; 148–156 bhp) at 6000 rpm (199 Nm; 147 lbft) at 4250 rpm

87 kW (118 PS; 117 bhp) at 4500 rpm  (190 Nm; 140 lbft) at 4500 rpm (PHEV)

See our separate 4B11T tuning article.

Tuning the Mitsubishi 4B1 and best 4B1 performance parts.

Best 4B1 upgrades

The greatest 4B1 upgrades on an engine are typically the ones that give the biggest return for your cash.

We won't be swayed by popular 4B1 upgrades, they need to be cost effective.

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 bhp gains are on offer for camshaft upgrades.

Fast road camshafts tend to raise the power across the rpm band, you may lose a little bottom end power but your top end will be better.

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

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

You should ideally optimize your power band to your usage of the car so for a road car stick with a shorter duration 4B1 cam

Different 4B1 engines respond better to less aggressive cam durations so view each engine as unique.

The ecu map and fuelling 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.

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Best Engine Mods for your car

  1. Engine Tunes - engine tuning/remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.
  6. Typical stage 1 mods often include:
    drilled & smoothed airbox, Remaps/piggy back ECU, Sports exhaust header/manifold, Fast road camshaft, Panel air filters, Intake manifolds.

    Typical stage 2 mods often include:
    Sports catalyst & performance exhaust, Ported and polished head, fuel pump upgrades, induction kit, high flow fuel injectors, Fast road cam.

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

    Plan your options and then buy your parts and set yourself a power target to save yourself from expensive mistakes.

    ECU mapping will help to establish the full potential of all the upgrades you've done to your 4B1.

    (In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

    It will usually give you around 30% more power on turbocharged vehicles and you can expect to see around 15% on NA (naturally aspirated) engines, but figures achieved will differs on the upgrades you've carried out and the condition of your engine.

    It is the whole point to any engine tuning project to pull more fuel and air into your 4B1

    Intake take the air during the suck phase from the intake filter and allow it to be fed into the engine cylinders.

    Structure and flow rate of the Plenum can make a substantial change to fuel delivery on the 4B1.

    Commonly we find the intake manifolds are improved through motorsport parts, although a few makers provide decently flowing intake manifolds.

    Big valve conversions on the 4B1, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also boost performance, and importantly will allow you to get a better performance increase on other upgrades.

    4B1 Turbo upgrades

    NA (naturally aspirated) 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 excellent power gains.

    If a car is fitted with a turbocharger mods are giving better power gains and we find turbo engines use more solid components.

    There are tuning limits for every engine, with some being incredibly solid and some only just able to handle stock powerIt is important to find these restrictions and fit forged components to handle the power.

    There are many car owners spending a fortune on turbocharger upgrades on the 4B1 only to have the engine explode soon after it's finished.

    Bigger upgraded turbo units tend to experience a bottom end lag, and small turbo units spool up really quickly but won't have the peak end bhp gains.

    Over the last 20 years the selection of turbos is always increasing and we now see variable vane turbos, allowing the vane angle is altered according to speed to lower lag and increase top end power.

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

    It is common that there is a limitation in the air flow sensor AFM/MAP on the 4B1 when loads 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 limited power at a much lower level.

    Adding a supercharger or additional turbo will make large performance gains, although more complex to configure. We have this article covering twinchargers if you want to read more.


    Don't overlook the need to raise the fuel delivery when you are increasing the performance - it makes the car more thirsty. It makes sense to over specify your flow rate on the injectors.

    The accepted safe increase is to add 20% to the flow rate when buying an injector, this accounts for injector deterioration and allows a bit of spare capacity should the engine need 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.

    All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58psi of fuel pressure at idle.

    4 Cylinder turbocharged engines

    • 58 PSI 340cc/min 200hp
    • 58 PSI 511cc/min 300hp

    4 Cylinder NA (naturally aspirated) engines

    • 58 PSI 285cc/min 200hp
    • 58 PSI 426cc/min 300hp

    4 Cylinder supercharged engines

    • 58 PSI 312cc/min 200hp
    • 58 PSI 468cc/min 300hp

    4B1 Performance Exhausts

    Only look to increase your exhaust if the current exhaust is actually creating a restriction in flow.

    On most factory exhausts you'll find the exhaust flow rate is 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 can help equal out the flow of gases through the engine.

    But if your exhaust is too large, ie: it's over 2.5 inches bore, you will lose a great deal of your flow rate and end up lacking power and torque.

    Usual exhaust restrictions can be traced to the filters installed, so adding a faster flowing sports alternative is the answer. This keeps the car road legal and will flow much better due to it's higher internal surface area and design, so has the added benefit of keeping your car road legal. The alternative decat should be considered an off road only mod, as removing a catalyst is illegal in most territories and regions for road registered cars..

    Weak spots, Issues & problem areas on the 4B1

    The 4B1 engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.

    Carbon build up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

    Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to this engines design, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

    Regular oil changes are vital on the 4B1, especially when tuned and will help extend the life and reliability of the engine.

    If you would like to know more, or just get some friendly advice on Tuning your 4B1 engine please join us in our car forums where you can discuss 4B1 tuning options in more detail with our 4B1 owners. It would also be worth reading our unbiased Mitsubishi tuning articles to get insights into each modification and how effective they will be for your car.

    Please help us improve these tips by sending us your feedback in the comments box below.

    We love to hear what our visitors have got up to and which upgrades work best for you on your car. Which helps us keep our guides and tips up to date helping others with their modified car projects. Your feedback and comments are used to keep this page up to date, and help improve the accuracy of these 4B1 tuning guides which get regular updates and revisions.

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