Tuning the Citroen XU

"Comprehensive guide to tuning the Citroen XU engine!"

We are regularly seeing threads requesting info on the best tips on XU upgrades. So let us look into Citroen XU parts and outline the best upgrades on this great engine and point out some common pitfalls along the way.

In this article we look into XU tuning and outline the greatest modifications for your car. Citroen XU great bases for a tuning project and with carefully picked tuning upgrades like ECU maps, turbo kits and camshafts you will dramatically increase your driving pleasure.

The optimum XU upgrades on an engine are usually the ones that give the best value for money.

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

Altering your XU cam will make a dramatic difference to the engine torque. Choosing a higher performance cam profile raises the torque accordingly.

NB: Fast road cams commonly bump the bhp and torque over the rev band, you may sacrifice a little low down power but your higher rpm power will be lifted.

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

A Competition cam is not great on the daily commute.

You should ideally optimize your bhp range to your cars usage so for a typical daily driver stick with a shorter duration XU cam

Different XU engines respond better to different cam durations check your engine on a rolling road.

The map and fuel pump and injectors also have a large bearing on the torque gains you'll achieve.

Longer 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.

XU Tuning Stages

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

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

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

Plan your options and then buy your modifications and set yourself a power target to avoid disappointment.

A remap allows a tuner to release the full potential of all the upgrades you've done to your XU.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your results usually rely on the upgrades you've done and the condition of your engine.

It is the main goal to any engine performance tuning task to push air and fuel into the XU engine

Headers take the air during the suck phase from the air cleaner and allow it to be sucked into the engine cylinders with fuel for the squish phase.

Shape and flow rate of the Headers can make a substantial improvement to fuel mixing and power on the XU.

We often see air intake manifolds are improved through aftermarket parts, although a few makers provide well optimised air intake manifolds.

Larger XU valves, doing a bit of port matching and head flowing will also increase power, the fantastic side effect is it will raise potential for a better power increase on other modifications.

Turbo upgrades for the XU

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 XU

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.

When your car has a turbo already fitted upgrades are going to net you a larger power gain and turbo charged engines are built using better components.

There are weak spots for every engine, with some being extremely strong and some only able to handle stock power

It is important to find these limits and install higher quality crank and pistons to cope with the power.

It's not unheard of tuners spending a lot of money on turbo upgrades on the XU only to suffer the indignity of watching the car explode just after it's completed.

Big turbo chargers commonly suffer a bottom end lag, and low capacity turbo chargers spool up really quickly but don't have the high rpm engines power gains.

In the last 10 years the market of turbochargers is always increasing and we now see variable vane turbochargers, where the vane angle is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbochargers divert the exhaust flow into a couple of channels and direct these at differently designed vanes in the turbocharger. They also increase the scavenging effect of the engine.

It is not unusual that there's a limit in the air flow sensor MAF/MAP on the XU 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 was restricting bhp at a much lower level.

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

Uprating XU fuel injectors

You will need to ensure that the engine is not starved of fuel so need to uprate the fuelling when you start exceeding 20% of a bhp increase.Most tuners we speak with say to be generous with your injectors flow rate.

The rule of thumb is to add 20% to the flow rate when fitting an injector, this takes into account injector deterioration and gives you some 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 XU performance exhausts

You should look to uprate your exhaust if your exhaust is actually creating a restriction.

On most factory exhausts you should find that your 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 help balance the flow of gases through the engine.

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

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

Problems and issues to look out for on the XU

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

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

For more information on Tuning your XU engine please join us in our friendly forum where you can discuss tuning options in more detail with our XU 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 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 XU guides and tips are kept up to date.

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