Subaru WRX STi Tuning

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In 95 we saw Subaru's Tecnica International tweaked WRX versions (STi) which had blueprinted engines, and many upgraded and stronger parts compared to the WRX. It was also specially tuned, and boasted a revised suspension setup and had a different transmission to the WRX.

The first generation STi versions were only available in the JDM market and we have started to see imports appearing around the world.

The STi did very well in world rally helping Subaru establish a great reputation and following.

By 2007 the STi became available around the world and a large number of special editions were released.

Subaru WRX STI Takumi (2008)

A concept vehicle based on the Impreza WRX STI hatchback with upgraded suspension lighter 12-spoke wheels, various engine tweaks and a slightly reworked bodywork.

20th Anniversary Edition WRX STI (2008)

A special 300 unit version of the Impreza WRX STI hatchback for the Japanese market featuring a commemorative plaque on the centre

WRX STI spec C (2009)

Limited to 900 units the Impreza WRX STI aimed at the Japanese market. The tubo bearings were revised giving a better reponse. Suspension and weight reduction was also provided on this model.

WRX STI A-Line (2009)

This had a five-speed semi-automatic, with steering wheel paddle shift. The vehicle went on sale initially in the JDM area and later also in Hong Kong, and later in Thailand, Indonesia, and Australia in 2011.


A special UK market version, tweaked by Prodrive. The WRX STI 330S includes increased engine power to 325 hp. The WRX STI 380S includes increased engine power to 375 hp, new wheels, an upgraded body kit.

NB: The 380S version was not be produced, due to homologation and specification difficulties. The regular 330S model did enter production as the "WRX STI Type UK".


The R205 was an awesome  complete car from STI; the "R" for "road". Specially tweaked for the road, from experience gained in motorsports.Uprated Brembo 13-inch discs and calipers were installed on the front and rear brakes. Supension tweaked made this stand out as a great handling WRX STi

WRX STI Special Edition (MY 2010)

Targetted and made for the North American market, it shared much with the Japanese STI Spec C. It included

WRX STI tS, WRX STI A-Line tS (2010)

Just 400 units were made of this special Impreza WRX STI sedan for the JDM

Cosworth WRX STI CS400

The Cosworth WRX STI CS400 is a limited (75 units) version of the Impreza WRX STI for the UK market. It includes a Cosworth-tuned version of the standard STI engine rated at 395 hp and various Cosworth badged body parts. Suspension and handling were specially tuned to allow the driver to exploit the extra power.

The "Cosworth WRX STI CS400" 


It is a limited (300 units) version of the Impreza WRX STI sedan for the JDM

WRX STI A-Line type S (2011)

It is a version of the Impreza WRX STI A-Line 4-door sedan and 5-door hatchback for JDM

Impreza G4 STI (concept; 2012)

It is a version of the Japanese model of the Subaru Impreza (4th Gen) G4 2.0i-S

Impreza WRX STI Group R4 (2012)

The Impreza WRX STI Group R4 is a full blown race car version of the Subaru Impreza WRX STI sedan built for the Intercontinental Rally Challenge.

WRX STI, WRX STI spec C, STI A-Line type S Package (2012)

Various performance upgrades and styling improvemnts made this model stand out.


A limited 300 unit version for the JDM.

The WRX STi is a good tuning project to carry out. We see many people wasting money on their WRX STi doing the wrong mods and then having to start over. Follow our tips to avoid wasting your money

Tuning tips and articles

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


Handling/Suspension upgrades

Many WRX STi owners uprate the handling of their cars with modified suspension mods as a priority, this will certainly increase your enjoyment of the car.

Good suspension tweaks that often improve handling for the WRX STi include a couple of degrees negative camber and 1-1.5 degrees of toe in or out on the front wheels. Toe in for stability, or Toe out to improve cornering. It would also pay to improve the brakes, by adding larger discs and or higher friction pads..

Drop the car by as much as 25mm - 40 mm and fit sports stiffer dampers, bigger drops will need other modifications in most instances.

Our aim in WRX STi engine tuning should be to increase peak power and Torque at the top end.

Keep the car looking standard and remove the badges for the ultimate sleeper!

Sadly with smaller engine sizes you are wasting your time spending money on modifications, so if this applies to you get yourself an engine swap then apply the following mods.

Engine tuning mods.

Typically these performance upgrades are usually carried out by our members, decide how far you wish to go in your tuning project before you get going.

Getting the right uprated parts for your planned usage of the car is essential. Stage 3 motor sport parts just don't work well on the road difficult in stop start traffic.

Typical stage 1 mods often include: Lighter flywheel, Suspension upgrade (drop 30-40mm), Panel air filter, Alloy wheels, Sports exhaust, Remap.

Typical stage 2 mods often include: high flow fuel injector, Power/Sport clutch, Fast road cam, Ported and polished head, fuel pump upgrades.

Typical stage 3 mods often include: Engine balancing, Competition cam, Adding or upgrading forced induction (turbo/supercharger), Sports gearbox, Internal engine upgrades (pistons/head/valves).

Your targets when tuning the engine should be a wide torque curve. You don't want all the torque to be at the top end unless you are creating a competition car.

The whole aim of our hints is to give a limited introduction of tuning modifications and point you in the right direction, our forum is where you can ask for more detailed advice and tips on your car tuning project, the best performance kits and all aspects of modding cars.One of the most cost effective mechanical uprated parts you can do to your NASP engine is to fit a fast road camshaft .

The intake & exhaust durations play a large part in your cars power band, but be careful here, getting this wrong can upset the idle and make the car hard to drive in traffic. You'd need to follow a camshaft upgrade with other mods and finish with a reflashed ECU for the best performance gains.

Don't forget to ramp up the fuelling when you are increasing the power - it makes the car more thirsty.

Most power losses, flat spots and erratic idling after upgrades are done can usually be traced to timing or fuelling issues.Upgrading the injectors is another beneficial modification and will deliver sufficient fuel.

If you are increasing your fuelling with bigger injectors you will also need to get a bigger fuel pump to supply it.

Intake and Exhaust Tuning.

Breathing mods are usually next up. Air induction kits only help to boost performance if your air intake is restricted! Adding an induction kit to most standard engines will see NO LOW END POWER GAIN AT ALL. If you have heavily modified your engine and it's need for air INCREASES DRAMATICALLY then an induction kit is the answer and will help remove this restriction.

Derestricting the flow of air into the engine is a primary goal of car tuners so get a better flowing air filter if you find that the car is running lean only if you find the car is running lean. Induction kits can sound sporty but due to the warm air in the engine bay they will not do much to increase power and often rob you of power.

Do not go with the biggest exhaust you can get this will slow the exhaust rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Polishing and porting the head will allow you to maximise your air/fuel charge. Leave this to a professional though with a proper flow bench and machine tools Your clutch can lose you loads of power as the power goes up if it starts to slip and the standard clutches are only ever good for power gains of up to 48%. Fit a competition clutch to avoid power loss through the transmission. The best mods in our experience for your WRX STi are remaps, sports camshafts and induction improvements.

Remaps offer massive power gains on all turbo charged cars. On NASP engines the benefits are doubtful. However a remap on a NASP engine will help unleash the potential if you have done a lot of mods.

We've also seen some tuners toying with twincharged conversions and making some seriously high power figures.

Adding forced induction will see large power gains but this is usually too expensive to be cost effective. It is often cheaper to bolt on a supercharger than it is to fit a working turbo. Turbos give boost in exponential proportion to rising engine speed and this can make mapping difficult.

The nice correlating boost and rpm characteristics of the supercharger make them simpler to map. To cope with forced induction you will usually need to decrease the compression ratio of the engine .

Alloy wheel upgrades.

The benefits of alloy wheels include lowering your unsprung weight and better brake cooling via the extra air flow they allow. Get a good directional tread pattern tire to improve your handling and help improve traction on your WRX STi. Please note that although they can look cool on the WRX STi big alloy wheels will actually decrease your performance. The larger you go the lower your acceleration will be - this to the change in your effective final drive ratio.

For this reason aim to keep the overall rolling diameter of the wheel the same as supplied from the factory. In all cases not going over 18 inches.

If you would like to know more, or just get some friendly advice on Tuning your car please join us in our friendly forum where you can discuss WRX STi options in more detail with our WRX STi owners. It would also be worth reading our unbiased Subaru tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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 mods work best for them on each model of car. Comments are used to improve the accuracy of these articles which are continually updated.

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