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Engine upgrade guide for MY11 and onwards Turbo Subaru STi 2.5 litre engines

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!.

SUMMARY
Typically this car is a "Subaru's peak performer" and a high performance car. Treating it like a basic road car and not maintaing it correctly will result in future costly repairs an maintenance.
There are some great features of this car, stealthy "new" looks (compared to past models), Auto option, 4wd, turbo 2.5 litre and most of all, a sensible budget with some well planned upgrades and it turns a great performance car into a super car beater!

TRANSMISION Vs POWER
The below points all relate to both the Auto and the 6 speed models, however the Auto model is even MORE detuned (than the 6 speed) and as such creates a huge opportunity for improvement with a correct retune of the factory ECU with EcuTeK software and a full retune. 
See dyno data. (links at bottom of this document) 

ENGINE WEAKNESS's
Bottom end performance can be dramatically improved with ECU tune.


The engine is detuned when delivered by the factory.
Poor long term durability with the factory standard Hypereutectic pistons can be troublesome in some cases but this should not be used as an excuse for not imporving this engine with correctly chosen tuning upgrades.
Poorly designed upgrades magnifies the risk of piston ring land failure that results in high oil consumption due to cracks in the piston skirt.
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 resulting in solid low end improvements. 
Car MUST be run on 98 Ron Fuel unless a optional custom (EcuteK) ECU retuned map is done. (cna be custom tuned to ANY fuel)
The turbo is reliable, giving great opportunity for improvement, but if over boosted with boost controllers etc will result in costly failures.
Be careful with increased boost on this engine, poor tuning or lack thereof, will significantly increase risk of piston failure. 

 

ENGINE SENSORS
On this model the aif flow meter sensor is reliable, but can suffer contamination due to dirt and poor filtration and in turn this will effect reliability and performance. (see MRT for this solution)
Often overlooked by dealers and workshops a careful clean of this sensor will result in better economy and power!
The twin rear exhaust O2 sensors if located incorectly 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.

FACTORY ECU
(All Australian models 2011 - onwards)
Can be converted and fully retuned, using EcuteK Software for almost any improvement, ECU is same design as previous (MY10) models and allows solid, good value 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.
there is no need to replace the ECU on this model.
An ECU tune such as this is the first and best value upgrade to be done on this car, even before a modified exhaust is considered. 

INTERCEPTOR ECU OPTION
Not worth considering as the intercptors simply do not have enough options to tune and modify the latest technology ECU control inputs.
ZERO VALUE

NEW (replacement) ECU
Factory ECU (EcuTeK) retune is best value unless a really serious engine rebuild is chosen. (IE over $25k) 
See notes above

INTERCOOLER
Factory fitted unit is huge and hard to beat, comes with silicone connector pipes.
MRT replacement TMIC is slightly better, but ask for advice as to when to fit it when choosing other options. This is only a benefit if other mods such as exhuast and ECU tune have been done OR in hot environments where the benefit is pronounced.
Hence choose carefully. 

INJECTORS
Bigger injectors empty your wallet and add no power unless part of a E85 fuel retune or major engine rebuild. 
Save your $$ for suspension and get some GOOD improvements.
OEM Injectors are big enough unless you do a major engine rebuild.

FUEL PUMP
More than adequate up to 50 kw at the wheels after that a 500 hp pump can be retrofitted

EXHAUST
(Some traps for people here, unless carefully chosen.)
The "new" quad outlet design on this model resulted in a more sporty note, mainly due to the "inboard" location of the outlets, that look odd and unusual.
Should ONLY be done at same time as a EcuTeK ECU tune to correctly match benefits, fit an exhaust with no ECU tune and the risk of engine failure with excessive fuel consumption will result.
Single scroll turbo engine pipes with hand made split collector to fit wastegate is necessary and will add throttle response and is good value, with the correct complete design. High flow metal cat in the downpipe is best.
Flex joint is needed as well, with correctly located O2 sensors.
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 restirctive and on the (Sedan the twin mufflers) and adds no value in just replacing this and should be completed as a part of a whole turbo back exhaust kit.
In some cases depending on final tune the twin mufflers in sedans can be re used with a complete exhaust, consult MRT for this. 

AIR INTAKE
Other than a intake noise no power here. 
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.

ENGINE ANCILLIARIES
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 as this model now has stretch fit belts and no adjustment like earlier models.
If fitted a kit or alloy crank pulley will result in snappy throttle response.

TURBO
OK if you have big bucks a turbo upgrade will add power, but be careful the OEM turbo is best kept in place as the limit is in the engine NOT the turbo and will give no value unless you plan a big engine upgrade.
(meaning if you fit a bigger turbo you cant use its benefits as the engine wont be capable of the extra boost)
If you want big grunt and big torque then ok, this is an option here, then you need to plan a engine rebuild.
Modest boost increases matched with the factory ECU boost controller via a custom ECU tune and EcuteK will result in benefits here. 

ENGINE INTERNAL
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 Pistons and Rods. 

BLOW OFF VALVE
Factory unit is ok, however a replacement BOV will result in slight benefits with a more sharp and snappy throttle response and also ads the option of externally or internally venting to get that chosen whoosh noise. 

OTHER OPTIONS
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.

IE:

  • 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.

SUSPENSION
check out the performance / suspension section for REAL gains and benefits.
If I owned a Sti suby, I would invest some of my budget in brakes and suspension as this is guaranteed BEST VALUE!
more here http://mrtperformance.com.au/performance/suspension

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

PRIORITY LIST

  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 for 6 speed models
  10. New Top Mounted Intercooler.

OTHER RESOURCES


 

Select Tune Level

EcuTek

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Find out why your Mitsubishi, Subaru, Mazda car is detuned by the factory Learn More ECU

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