Subaru WRX STi Tuning

"Thanks for reading my guide to modifying and tuning the Subaru WRX."

Let's look at the best mods and upgrades for the Impreza WRX, the WRX and the WRX STi. These are very special cars and if you are looking to buy one, then it makes sense to get an overview of their history. After this overview we shall look at mods and tuning parts to help you take your WRX to the next level.

If you just want some mild tuning upgrades for your WRX, or wish to turn it into a trackday monster this is the page for you.

We often get asked about the best mods, best turbo upgrades, injector upgrades and performance exhausts for the WRX, so I will keep this page up to date, based on what our members, readers and channel viewers are doing.

Bear in mind that not all Impreza mods and upgrades will be adding power, often they just remove restrictions or bottlenecks that happen after you've hiked the power.

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.

Subaru WRX Mods & Performance Upgrades

If you own an WRX you have a very special car indeed, with a rich pedigree and history. However, as with most owners of any performance car, you could always do with more power.

So can the WRX be tuned and further improved? Yes and there are many options and upgrades for them. So we will pull out the best options you have and flag up the main areas you should focus on.

Please review our model specific guides where we can be less general and start recommending parts, based on what other owners have tried and tested out.

Impreza WRX Engine Mods & Tuning Guide.

Please watch our video which covers the 5 principles of tuning your Impreza WRX. Be sure to keep up with our latest YouTube content and subscribe.

Best Impreza WRX Mods

1. Braking Mods - Improve your ability to stop needs to be listed in your priority list.
2. Fast road Camshafts are are often the best upgrade for an engine, but they must be installed by someone qualified to set them up and tracking one down may be hard but you'll probably find a local firm to regrind a stock cam for you.
3. Forced induction upgrades - A New Turbo is the most efficient approach to increase air supply, ensuring you are able to utilize more fuel and make more power. Typically one of the most costly upgrades but provides the best gains.
4. Engine Tunes - A Remapped Impreza WRX ECU ensures the most advantage compared to your outlay, aftermarket ECUs, and Tuning boxes are all alternatives.
5. Flowing and porting the Head - Head work will get air flowing into the engine while removing turbulence or restrictions.
6. Impreza WRX Handling Mods (Suspension) - Upgrading your suspension dramatically improves Impreza WRX handling Poly Bushes and Coilovers are typically fitted to achieve this
7. Intake Mods and Sports Exhausts - NB: on their own these mods will NOT ADD HP , but they permit you to release power after other upgrades by losing a restriction.
8. Low mass flywheel - a lower mass flywheel will improve the engines free revving nature. Not always recommended for all Impreza WRX engines.

Impreza WRX Tuning Mods in Stages

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

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

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

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.

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

Let’s take a look at some of the performance modifications that can be done on the Subaru WRX models:

Air/ Oil Separator

The Subaru WRX is a great car. However, a common issue that is faced by multiple owners of this car is the excessive amount of oil inside the engine ventilation system of the vehicle.

This is an issue that is not particular to the WRX rather all vehicles with turbocharged engines suffer from this problem to some extent due to the excessive blow-by.

If the car doesn’t have an air/ oil separator, the oil level in the vehicle will reduce. This can lead to knocking.

An air/ oil separator is also known as AOS and we recommend that you get one for your Subaru WRX to resolve this common issue.

WRX Improved Air Intake System

While a turbocharger is effective for increasing power, the most common issue is that factory-fitted parts are often quite restrictive, limiting the amount of air available to the engine.

Thankfully the WRX intake copes well at stock power levels, but after you've added tuning mods there is an argument for fitting a less restrictive intake.

What happens if your engine is struggling to pull in enough air due to a restrictive intake?

The required mixture of air and fuel for combustion is not available in sufficient quantities, and the engine cannot deliver its peak performance having to trim back on the fuel.

The Subaru WRX is no exception, which is why upgrading the air intake system is one of the best ways to improve air flow to the engine.

The larger surface area of the filters in these air intake systems effectively solves the problem of restricted airflow.

Intercooler Mods

An intercooler is an effective mechanism for providing cold and dense air to the engine of your Subaru WRX.

This cold air considerably increases the performance of your vehicle and thus installing an intercooler is highly recommended for the Subaru WRX.

Improved Fuel System

When the air intake system of your Subaru WRX has been upgraded, the next major step is to install an improved fuel delivery system.

While the stock fuel system of the vehicle is sufficient for meeting the needs of an unmodified vehicle, the dynamics change altogether for modified vehicles.

That’s because the amount of fuel required by these vehicles is much higher than that required by an unmodified vehicle.

The installation of upgraded fuel pumps, fuel pressure regulators, and fuel injectors allows the vehicle to ingest more fuel, and when this fuel is mixed with augmented quantities of air supplied by the upgraded air intake system, the resulting combustion rate is much higher than normal.

This means that the power generated by the car is considerably increased.

Performance Radiator Upgrades

One of the most common issues faced by modified vehicle owners is overheating.

The major reason behind this issue is that the stock system installed in the vehicle is just not capable of handling the increased heat produced by higher combustion rates.

This is where the need for an aftermarket radiator comes into play. These performance radiators are designed to dissipate heat quickly thereby enabling the vehicle to stay cool.

WRX Improved Exhaust System

This mod is very common, and really enhances the distinctive burble from the flat 4 boxer engines. How an improved exhaust system can affect the performance of your car might surprise you. 

This is true for the Subaru WRX as well and thus by installing an aftermarket exhaust system, the performance of your vehicle can be considerably improved.

Bear in mind the stock exhaust flows really well, and does not present a restriction until you've been adding power mods.

You have various options available in this regard. Thus you can choose a cat-back exhaust that meets your preferences.

Some of the common manufacturers offering aftermarket performance exhausts for the Subaru WRX include but are not limited to:

• Injen;
• GReddy;
• HKS
• Buddy Club;
• Corsa.

These exhausts increase the power and torque of the vehicle and besides this, the rumble of the vehicle also gives it an aggressive stance.

The improved flow of exhaust gases aids in keeping the engine temperature relatively low.

Tuning The WRX - One of the Best Mods

Installing an air intake, intercooler, improved fuel delivery system, and performance exhaust will significantly improve the performance of your vehicle. However, one factor that you simply cannot ignore is tuning.

This involves changing the WRX Ecu mapping and can be achieved in a number of ways. Early models require piggyback ECU, Aftermarket ECU's and Quality Tuning boxes, and later models can be flashed or bench flashed and updated by specialist tuning companies. There are even a few companies selling premade map files for DIY installation.

By properly tuning your car’s engine, you get to make the most out of your Subaru WRX.

It is also worth noting that if your WRX is not properly tuned, it will run poorly and deliver significantly less power than its potential.

Another way that tuning your Subaru WRX can be extremely beneficial is that you can use alternative fuels such as ethanol. This reduces the likelihood of knocking significantly.

Tuning will also improve the fuel efficiency of your Subaru WRX. So have your vehicle tuned by an expert is a recommended step that you should not skip.

This should always be the last tuning mod you apply as it will unlock all the other mods, and can be customized and optimized for your individual WRX.

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.

WRX STI 330S / WRX STI Type UK & WRX STI 380S

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".

WRX STI R205

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 was tweaked  and this made this stand out as a great handling WRX STi

WRX STI Special Edition (MY 2010)

Targeted 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.

WRX STI S206, WRX STI S206 NBR CHALLENGE PACKAGE (2011–2012)

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 improvements made this model stand out.

WRX STI tS Type RA, WRX STI tS Type RA NBR CHALLENGE PACKAGE (2013)

A limited 300 unit version for the JDM.

Tuning Mod Summary

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

The best mods in our experience for your WRX STi are remaps, sports camshafts and induction improvements.

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.

One of the most cost effective mechanical uprated parts you can do to your NA (naturally aspirated) 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. 

Remaps offer massive power gains on all turbo charged cars. On NA (naturally aspirated) engines the benefits are doubtful. However a tune/remap on a NA (naturally aspirated) 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 .

WRX 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 optimally somewhere in the region of 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.

To be completely frank and honest, on the more modest 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

Alloy wheel upgrades on the WRX.

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.

Problems to look out for on the WRX

According to the owners, Subaru Impreza is subjected to internal engine failure. Some of its known weak points are rods, pistons, rod bearings, piston bearings, and other moving parts, which tend to cost heavy to replace or repair.

Oil and gasket leaks tend to damage the engines in the long run. Some turbo failures with the newer WRX models were also reported due to wear and tear.

Tuning put a lot of stress on the turbocharged vehicles, so strengthening components will help prevent many problems.

Throttle shafts are unsteady and STI suspensions are rough. The ride became uncomfortable due to sudden hard blows when on a bumpy road. Despite above issues with some models, Impreza won many awards from the day of its inception till now.

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.

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