Modding uprating the Fiat Multijet engine!

Tuning guide "Multijet Modifications"

Multijet Modifications Guide

How to modify and upgrade the Fiat Multijet

"Comprehensive guide to tuning the Fiat Multijet engine!"

Sites like TorqueCars are always getting posts asking about how to improve the Multijet from people inquiring about getting more power from the Multijet and wanting to know what are the greatest Multijet upgrades. So let us look into Fiat Multijet upgrades and outline the best upgrades on this great engine and point out some frequent tuning mistakes along the way.

The Fiat Multijet have loads of potential and with carefully chosen mods like a remap, turbo improvements and camshafts you will certainly enhance your driving fun.

Car Tuning Tips will review and look at Multijet tuning and show the premier upgrades.

When talking about the best parts for your Multijet engine, we are going to concentrate on the mods that give the best power gain for you spend.

Multijet induction kits

Improving air intake on the Multijet

You need air matched to fuel for an engine to work. If there is not enough fuel then it will run lean, if there is insufficient air it runs rich sapping power which risks damage to the Multijet. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So the fundamental goal to any tuning task to pull air into your Multijet but this has a knock on effect with the air flow sensor.

It is common that there is a limitation in the air flow sensor MAP/MAF/AFM on the Multijet when loads more air is being drawn into the engine.

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

Headers flow the on the suck phase from the air filter and allow it to be pulled into the engine cylinders.

The shape and flow characteristics of the Intake headers can make a big effect on to fuel delivery on the Multijet.

It's not uncommon that headers are in desperate need of a performance upgrade, although a few OEM provide well optimised headers.

Fitting big valve kits, carrying out 3 or 5 angle valve jobs and porting and head flowing will also boost bhp and torque, this will make space for an improved bhp and torque increase on other tuning mods.

Multijet performance cam tips.

Different Multijet engines respond better to 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 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.

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

NB: Fast road camshafts commonly push up the bhp through the rev range, you may sacrifice a little bottom end bhp but the higher rpm power will be better.

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

In a car driven daily you need to match your engines power to your preferences.

I'd be amazed if you have found a Multijet Race camshaft is a pleasure to live with when in heavy traffic.

Stage 1, 2 and 3 mods for the Multijet

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 Multijet parts:

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

Stage 2 Multijet parts:

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

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

Stage 3 Multijet parts:

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

Carefully think through your options and then buy your upgrades and set yourself a power target to avoid disappointment.

ECU flashing will help fully realize the full potential of all the parts you've done to your Multijet.

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 may vary depending on the parts you've done and the condition of your engine.

Turbo modifications on the Multijet

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 Multijet.

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 turbo already fitted upgrades are more reliable and turbocharged engines will have better components.

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

Discover these limitations and upgrade to forged components to cope with the power.

We've seen drivers spending a lot of money on turbo upgrades on the Multijet only to suffer the humiliation of seeing the whole thing go up in smoke just after it's used on the roads.

Larger capacity turbochargers often suffer no power at low rpm, and small turbochargers spool up quickly but won't have the peak rpm bhp gains.

Thanks to new tech the range of turbochargers is always developing and we are seeing variable vane turbochargers, allowing the vane angle is altered according to speed to lower lag and increase top end torque.

Twin scroll turbochargers divert the exhaust flow into two channels and flow 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 challenging to configure. We have this article on twincharging if you want to read more.

Tips about fuel supply on the Multijet

You will need to ensure that the engine is not starved of fuel so will have to increase the fuelling when you start extending past 20% of a torque hike. We strongly recommend you to over specify your injector capacity.

The accepted safe increase is to add 15% to the flow rate when buying an injector, this takes into account injector deterioration and allows a bit of spare capacity should the engine require 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 Multijet performance exhaust upgrades

Only look to uprate your exhaust system with an upgraded one is if your current exhaust is actually causing a restriction in flow.

On most factory exhausts you'll find the exhaust flow rate is 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.

Note that with the largest exhaust you can buy you'll reduce the exhaust flow 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 are in the catalysts installed, so adding a faster flowing race 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 Multijet

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

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