Alphius wrote:I know this isn't relevant to your question, but...
Don't do this! Your car will run poorly! It might be faster than it is now, but it will be nowhere near its capability and it will be poor to drive anywhere but full throttle and it will be at much more risk of catastrophic failure.
Best setup for cheap, reliable power on one of these cars (I post this whenever someone asks about power upgrades):
RobTuned EJ20G ECU
550cc STI injectors
JECS (green label plastic) MAF
VF39 or TD05-16g turbo
06-07 WRX intercooler w/recirc BPV
Boost Controller at 17psi
Free-flowing exhaust
Stock intake with de-snorkel and coffee cup mod
Done. This will make about 220-230 AWHP on a bone stock EJ22T safely. Any more than that and you are looking at standalone ECU and tossing the MAF.
As far as the transmission goes, if you get the TransGo shiftkit it should last a little longer, and if it is already in good shape it should last pretty well with that power level. Just don't abuse it. Same advice I would give for someone with a 5MT.
220 - 230 AWHP - I'm not sure if you are quoting this power level at the wheels or at the crank. If it's at the wheels, that's plenty of power. What sort of MPG could you expect out of this setup? Must the exhaust system be 3" all the way back for everything to work nicely together? What, if anything, would change if you use an electronic boost controller? What, if anything, would change if you used an AWIC setup, instead of the 06-07 TMIC? Could a piggy back be used simply to provide an alternate map while using the Rob Tune Settings as a base map? BTW, don't feel you need to water down the answer so that I understand. I will understand just fine. I know the popular sentiment about piggy backs, but want to know if they have any value in the right setup. In this case, I'm thinking that the above setup is the best all around tune for every day. Meanwhile, I would like to see if it would be possible to run a higher boost map with the piggy back dialing in methanol injection and/or an extra fuel injector, and also an economy map, dialing down boost and possibly allowing using regular fuel for inexpensive around town driving. Rob tune base map would be for autocross, high boost for the occasional dragstrip run, and economy mode for around town.