Tuning the Fiat Multijet

"Comprehensive guide to performance tuning the Fiat Multijet engine!"

We often are getting messages about the best Multijet upgrades. So let us look into Fiat Multijet modifications and outline the best modifications on this great engine and point out some common pitfalls along the way.

The Fiat Multijet are good project engines and with carefully picked modified parts like ECU maps, turbo kits and camshafts you will really maximize your driving fun.

TorqueCars will review Multijet tuning and outline the greatest modifications.

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

Altering your Multijet camshaft will make a dramatic difference to the engine engines power. Choosing a higher performance camshaft profile raises the engines power accordingly.

NB: Fast road camshafts usually boost the performance throughout the rpm band, you could drop a little low end bhp but the higher rpm power will improve.

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

On a daily driver must carefully try to optimize your engines power to your usage of the car.

I would be surprised if you find a Multijet Competition cam is a pleasure to live with when in heavy traffic.

Different Multijet engines respond better to less aggressive cam durations so set your engine up on a rolling road.

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

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.

Multijet Tuning Stages

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

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

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

Carefully think through your options and then find your mods and set yourself a power target to save yourself from expensive mistakes.

ECU flashing helps unlock the full potential of all the tuning mods you've done to your Multijet.

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 usually differs on the tuning mods you've carried out and the condition of your engine.

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

The intake plenum transmit the air from the intake filter and allow it to be fed into the engine cylinders with fuel for the squish phase.

Design and flow characteristics of the Headers can make a large change to fuel atomisation on the Multijet.

On popular production engines headers are in dire need of a performance upgrade, although some manufacturers provide reasonably well designed headers.

Big valve conversions on the Multijet, getting Multijet port enlargement and head flowing will also lift torque, the fantastic side effect is it will allow you to get a better torque increase on other parts.

Turbo upgrades for the Multijet

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 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 excellent power gains.

If the engine has a turbo already fitted modifications are more reliable and we find turbo engines are built using strengthened components.

There are practical limits for every engine, with some being over specified and some only just able to handle stock power

Research these limits and install higher quality components to utilize the power.

It's not unheard of people spending a loads on turbo charger upgrades on the Multijet only to have the Multijet go up in smoke when it's been finished.

Large upgraded turbo chargers often experience no power at low rpm, and low capacity turbo chargers spool up much more quickly but do not have the peak rpm bhp gains.

We are pleased that the world of turbo units is always moving on and we now see variable vane turbo units, permitting the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbo units divert the exhaust flow into two channels and direct these at differently profiled vanes in the turbocharger. They also help the scavenging effect of the engine.

It is not unusual that there is a limit in the air flow sensor AFM/MAP on the Multijet when considerably more air is being sucked into the engine.

Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped bhp at a much lower level.

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

Uprating Multijet fuel injectors

You will need to ensure that the engine is not starved of fuel so need to increase the fuelling when you start exceeding 20% of a torque increase.Don't forget to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% to the flow rate when specifying an injector, which takes into account injector deterioration and provides 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 Multijet performance exhausts

Only look to boost your exhaust if the existing exhaust is creating a restriction in flow.

On most factory exhausts you'll see the flow rate is ok 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 usually air flow out of the engine but avoid an exhaust that is too big or you may end up will reduce the flow rate. Stick to 1.5 to 2.5 inches for best results.

Typically exhaust restrictions can be traced to the emissions filters installed, so adding a better flowing high performance alternative will help avoid this restriction.

Problems and issues to look out for on the Multijet

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

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

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

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