We get many calls for upgrades on this model, more so recently as this car is becomming even more affordable, as a guide to assist you we have created this list to save your time, guarantee your money is invested correctly and most of all give you maximum value!.

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Typically this car is a “Subaru’s fix for its first error as the MY02 / 03 was the ugly duckling we all grew to love”  it has good value potential and is a high performance car effectively detuned when compared to the STi model of the same year and later!
The MY03 onwas a lot like the previuous but with some obvious external changes (lights) and internal with trans and engine
There are some great features of this car, 4wd, turbo 2.0 litre and most of all, a sensible budget with some well planned upgrades and it turns a great car into a STi beater!
(Editor note, this model is a very detuned option, with sorry, to say the 2nd worst flowing heads (the My01 02 was worst) of any subaru turbo ever made, but some simple mods makes this bargain model  much better than the later model at a much lower cost)

Can be converted and fully tuned, using EcuteK Software for almost any improvement, ECU allows solid results with correct settings and allows good improvement.
The ECU in this model can also be upgraded to “EcuteK Race Rom” for added features that were never included in the Subaru ECU

Bottom end and mid range performance can be dramatically improved with ECU tune. The engine is very detuned (as subaru dont want it to beat the STi ) and also limited due to emisions requirements when delivered by the factory.
Poorly designed upgrades magnifies the risk of piston failure.
Run too much boost or too much ignition advance and the result will inevitably be piston failure
Boost and VVT cam maps, can be improved.
Has inlet tumble valve generators that restrict flow at high RPM and high boost.
Car should be run on 98 Ron Fuel unless a custom (ecuteK) map is done.
The turbo is but if over boosted with boost controllers etc will result in costly turbo failures.

On this model the aif flow meter sensor is more reliable than previous model, but can suffer contamination and in turn this will effect reliability and performance. (see MRT for this solution)
The twin rear exhaust O2 sensors if located incorrectly related to modified exhaust can cause problems, if old can also dull the cruise performance of the car and increase fuel use.
Crank, cam  and Knock sensors are reliable, but with age can fail.

Not worth considering as the intercptors simply do not have enough options to tune and modify the latest technoplogy control inputs.

Factory ECU retune is best value.
See notes above

Factory fitted unit is “OK”, dont fit a FRONT mount unless you plan a mosnter engine with resulting turbo to suit.
Use a better replacement MRT top mount, but choose carefully.

Bigger injectors empty your wallet and add no power unless part of a E85 fuel retune or MRT XC power kit that includes tune, zorst turbo etc.

Needs to be replaced with any mods over standard specification.

(Some traps for people here, unless carefully chosen.)
Single scroll turbo engine pipes with split collector to fit wastegate is necessary and will add throttle response and is good value, with the correct complete design. High flow ceramic cat in the downpipe is best.
Flex joint is needed as well, with correctly located O2 sensor.
Get this wrong and the car will suffer CEL lights, deactivate the Cruise control and cause poor fuel economy.
On hatch models the single rear muffler is not that restrictive and on the and adds no value in just replacing this and should be completed as a part of a whole turbo back exhaust kit.
Consult MRT for this.
This model deleted the privious mdoel that had a pre turbo cat converter thank goodness!

Other than a intake noise no power here.
MRT used to supply and fit Cold air intake and ram pod style intakes, but with technology and recent testing and on the later models these were made redundant. The positive intake pressure with the factory intake is best kept in place.
A replacement panel filter in the std airbox will save on future servicing but give no power improvement.

Items such as aftermarket plug leads, high capacity discharge ignition systems etc all will ad very marginal if any improvement.
A GFB alloy pully kit will fit some models, this model has a two part kit available.
If fitted a kit or alloy crank pulley will result in snappy throttle response.

If you have the budget a turbo upgrade will add power, (such as a MRT XC kit)  , but be careful the OEM turbo is best kept in place unless you have the right other parts to match a new turbo upgrade.
As the limit becomes close to the engine depending on your choice turbo and will give no value unless you plan carefully.
(meaning if you fit a bigger turbo you can use its benefits but be careful as the extra boost will need to be tuned carefully )

Like above if you have a solid budget, then a rebuild will give some great and huge benefits, but a rebuild will cost over $7k and then you need to choose carefully there are many options, but only if you REALLY want to.
Best value here first and foremost is 2500 cc STi short block and or new Pistons and Rods.

Is the car serviced correctly? Because often a service by a workshop who really knows subarus will be your best choice for first place for power and reliability.


  • Upper engine cleaner and in tank fuel additive. (when was this last done, its a subaru suggested option).
  • Good quality low friction engine oil such as Mobil 5 w 30 will give around 5 kw and better fuel economy over a non synthetic oil.
  • Fuel system service, MRT offer this and often get good results, cleans the EGR “gunk” out of the intake and combustion area.
    Also injectors as well as inlet manf and exhaust as well as fuel pump, lines and sensors.
  • Synthetic trans and diff oil, again like engine oil this adds up in benefits.
  • Timing belt, fuel filter are again areas that should be checked and renewed.

Check out the performance / suspension section for REAL gains and benefits.
If I owned this WRX suby, I would invest first in the MRT XB kit as it will then have more power than the later 2009 model, and then some of my budget in brakes and suspension as this is guaranteed BEST VALUE!
more here https://mrtperformance.com.au/performance/suspension

Refer the MRT vehicle service section here and take advantage of our free 78 point check to ensure your car is in top shape!


  1. Check service history.
  2. Check the O2 sensor
  3. Check brakes
  4. ECU upgrade and re tune.
  5. New brake pads and discs if needed
  6. Front and rear sway bars.
  7. Complete (quality) exhaust.
  8. Front and rear sway bar links
  9. Positive shift kit
  10. New Top Mounted Intercooler.


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