We get many calls for upgrades on this model, 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!.

Typically this car is a “Grand Touring car” and not a high performance car. Treating it like you epxect it to be a WRX or STi will result in costly repairs an maintenance.
However there are some great features of this car, stealthy looks, 4wd, turbo 2 litre and most of all, a modest budget with some sensible upgrades and it turns a good car into a great car!

As time moves on history is showing a greater amount of turbo failures with this model.
This is typically due to:
+ Poor maintenance. BUT MOSTLY
 + Incorrect mods with boost and the twin turbo system
please take the time to read on, so you avoid these costly problems!

(All Australian models 2001 – 2003 only)
Can be converted and fully tuned using EcuteK for almost any improvement, ECU is a early design but stil allows solid results with correct settings and allows good improvement.

Mid range drop in torque when the 2nd turbo opens can be dramatically improved with ECU tune.
Poor Ignition maps, due to excessive (factory set) ignition timing can be improved. Standard car originally in Japan was designed for 100 ron fuel and in Oz with 98 ron fuel engine pings badly when standard and only gets worse if modified incorrectly.
Car MUST be run on 98 Ron Fuel unless a custom (ecuteK) map is done.
Twin turbo’s are reliable, but if over boosted with boost controllers etc will result in costly failures.

With a EcuTek retune of the factory ECU the following will be gained

  • Substantial improvement (and reduction) in the mid range (VOD) or valley of death as its known there the primary turbo changes over the secondary turbo and the chrging of boost to the 2nd turbo causes a horrible drop in power on the standard tune.
  • Huge reduction in engine knock, that cuases long term bearing failure.
  • Noticable improvement in ignition timing maps that cause engine pinging even when run on 98 Ron fuel
  • Turbo comes on boost slightly earlier in low RPM’s
  • Substantial improvement in torque and miod range power
  • Fuel economy and power will vary with state of tune, some cars have horrible long term ignition correction by the ecu in an effort to reduce pinging and this then effects the out come when the ECU is retuned.
  • A tune can be supplied on 95 Ron if needed, but this will result in less performance.


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.
The single rear exhaust O2 sensor if located incorectly related to modified exhaust can cause problems, if old can also dull the cruise performance of the car and increaswe fuel use.
Crank, cam  and Knock sensors are reliable, but with age can fail. 

Not worth considering as the intercptors simply dol not have eniugh options to tune and modify the twin turbo control inputs.

NEW (replacement) ECU
Factory ECU retune is best value.

Bigger injectors empty your wallet and add no power. Save your $$ for suspension and get some GOOD improvements.
OEM Injectors are big enough unless you do a major engine rebuild.

(Big traps for people here, unless carefully chosen.)
Twin turbo engine pipes one with split collector to fit wastegate is necessary will add throttle response and is good value, with the correct complete design. Do NOT fit 3 in twin pipes, they are too big.
Flex joint is needed as well as sensible design for future easy removal of the transmission, high flow cat is needed with correctly located O2 sensor.
Get this wrong and the car will suffer CEL lights and poor fuel economy.
On some models the rear muffler has a cable operated bypass valve, via ECU control and will be seized, a sports stainless muffler is critical for the right back pressure and power.

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

Factory fitted unit is “ok”
Can be replaced with a better MRT unit with new inlet pipes, see schedule below as to “when”

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, but this varies with the alternator design. If fitted a kit or alloy crank pulley will result in snappy throttle response.

A replacement Blow Off Valve will add to a snappier throttle response, but give no increase in peak power. Run externally venting and the occasional CEL will occur with the downside of poor fuel economy.
The upside is adjustablity like a GFB Respons, or similar.

As the car is now aging a new fuel pump is suggested, if you plan ANY performance upgrades then its needed.
A MRT 500 HP pump will fit the factory location

OK if you have big bucks a turbo upgrade will add power, but be careful the OEM turbo’s are tricky to modify and will give no value unless you plan a big engine upgrade
If you want big grunt and big torque then ok, this is an option here, then you need to plan a engine rebuild.

OK like above if you have wads of cash, then a rebuild will give some benefits, but a rebuild will cost over $7k and then you need to choose carefully a 2.5 lite block is an option, but only if you REALLY want to.

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 a B4 suby, I would invest 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. Fuel pump.
  6. New brake pads and discs if needed
  7. Front and rear sway bars.
  8. New Top Mounted Intercooler.
  9. Complete (quality) exhaust.
  10. Front and rear sway bar links
  11. New Anti lift kit


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