Jaguar XJ Tuning

"More Cheetah than Jaguar really!"

The 2009 XJ revision is fresh and energetic. The epic makeover is not just skin deep, the fantastic engines on offer mean that the XJ performs as well as it looks.

We shall look at the various tuning options open to you. With some carefully chosen performance modifications you can dramatically maximise your driving fun and enjoyment of your car.

We will look at remapping, intake and exhaust mods and dispel a few commonly held myths. Don't waste money, do your homework and follow our unbiased guides to each performance upgrade to avoid disappointment.

Tuning tips and articles

Engine tuning Transmission tuning Care care Intake & exhaust mods Improve handling Forums

Handling modifications are usually your first port of call for the XJ. We suggest that you fit uprated suspension and lower the car by 30-35mm. Larger drops require arch work - especially on models already equipped with sports suspension.

Turning our attention to the XJ's engine, we need to get a bit more power out of the top end.

With our tuning guide your XJ can be a track day fun car and maintain it's reputation as a reliable daily driver.

The best power gains come from larger engine sizes. The more you start with the bigger the return on investment, so engine swaps are good value mods for small engined cars.

Tuning modifications.

This list shows the stages and mods that are usually performed by our members. Decide how far you want to go before you get started.

Getting the right mods for your planned usage of the car is a time and money saver. Stage 3 competition upgrades just don't work well on the road and are hard to control in slow traffic.

Stage 1 modifications: Panel air filter, Alloy wheels, Lighter flywheel, Suspension upgrade (drop 30-40mm), Sports exhaust, Remap.

Stage 2 modifications: Ported and polished head, Fuel injector & fuel pump upgrades, Power clutch, Fast road cam,.

Stage 3 modifications: Internal engine upgrades (pistons/head/valves), Sports gearbox, Adding or upgrading forced induction (turbo/supercharger), Engine balancing, Competition cam.

Your target when modding the engine should be a nice flat torque curve. You don't want all the power to be at the top end of the rev range, unless you are creating a competition car.

In this article we shall give an overview and introduction to the best mods for your car, but we'd encourage you to spend some time on the site looking into the details for each type of performance mod.

A fast road cam usually works out as one of the best NASP power mods you can do mechanically to your engine. The intake and exhaust flow play a large part in your car's power band, but be careful here, getting this wrong can upset the idle and make the car impossible to drive in traffic.

You'd need to follow a camshaft upgrade with other mods and finish with a remap to fully realise your gains.

You will need to ensure that the engine is not starved of fuel, so will need to uprate the fuelling. If you find you experience flat spots and power surges after your mods you should check the fuelling and try a higher octane fuel as well. To get sufficient fuel you may need to uprate the injectors on your engine. Uprate the fuel pump to cope with the extra fuel requirements of your tuned XJs uprated injectors.

Intake and Exhaust Tuning.

The next area for modification is the intake and exhaust. Air induction kits are only beneficial to increase power if your car's air intake is restricted. Adding an induction kit to most standard engines will see NO POWER GAIN AT ALL. If you have heavily modified your engine and its need for air INCREASES DRAMATICALLY then an induction kit is the answer and will help remove this restriction. Induction kits can work well on turbo engines and larger engines (if supplied with a suitable cold air feed or air box). Generally though, for XJ engines, we'd recommend you settle for a performance panel air filter, preferably made from cotton.

Sports exhausts can usually help the rate of air flow out of the engine, but avoid an exhaust that is too wide or you could reduce the flow rate. Stick to 1.5 to 2.5 inches as a rule of thumb.

Getting a professionally gas flowed head with larger valves can fully maximise your power gains. When you heavily modify your XJ you will often find that the standard clutch starts to suffer so get an uprated clutch.


Turbo engines are just asking to be Remapped. You will see very impressive power gains on most modern turbo charged cars including diesels, making a remap one of the most cost effective and impressive modifications for your money.

The most impressive power gains for NASP engines usually involve the addition of forced induction. It is often cheaper to bolt on a supercharger than it is to get a turbo working. With a turbo the power curve is related exponentially to the engine speed, making it difficult to map fuelling with it. The nice proportional boost and rpm characteristics of the supercharger make them more straightforward to map. Decreasing the engine's compression ratio will allow you to add forced induction, water injection may also help prevent detonation.

We've also seen some tuners playing with twincharging applications and making some seriously high power gains.

Alloy wheel upgrades.

Alloy wheels can help the brake cooling and are generally lighter than the steel ones. Please note that although they can look cool on the XJ, large alloys will actually decrease your performance. The larger you go the lower your acceleration will be - this is due to the change in your effective final drive ratio. Although some people have gone larger than this, we would restrict ourselves to an 18 inch rim size as the maximum.

For more information on tuning your car, please join us in our friendly forum where you can discuss XJ options in more detail with our XJ owners. It would also be worth reading our unbiased Jaguar tuning articles to get a full grasp of the benefits and drawbacks of each modification.

We need your help improving this article, so please send us your feedback in the comments box below and pass on any tips, points or facts we have wrong or have not covered. We really like hearing from our readers, and hearing about which mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our guides and tips are kept up to date.

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