These are the parts I recommend. I recommend them because they work and the companies actually care about the Subaru community.
- Process West or ETS Top Mount InterCooler (TMIC)
- CobbSF Intake w/ Box
- Cobb, Grimmspeed, Invidia Catted Turbo back exhaust (TBE)
- Cobb or Grimmspeed Electronic Boost Control Solenoid (EBCS)
- Perrin or Killer B Equal Length Header and Up Pipe
- Cobb 1050x Injectors (* 04-06 STi's will need a top feed conversion kit)
- Cobb Flex Fuel
- Cobb Fuel Pressure Sensor
- AEM 340 Fuel Pump
- Cobb Fuel Pressure Regulator Kit (08+ STi only)
- IAG TGV Deletes (only recommended if doing something that requires removing IM)
- Radium Catch Cans or IAG Street AOS
- NGK 1 Step Colder Iridium Plugs (0.028-0.030 gap for pump, 0.026-0.028 gap for e85 or larger turbo pump gas setups)
- AEM X-Series Wideband (part# 30-0300) w/ i-Wire plug n play harness
* Air pump deletes can cause startup fueling issues due to fueling compensations from undefined tables in the ECU. Deleting the air pump can/will cause oscillations during coldstart/warmup conditions. These can be worked around by running the car richer during startup which ultimately isn't great for cats and mufflers.
* Cobb does not make Stage2 CobbSF+TBE OTS maps because these cars are out of fuel with just an exhaust. If you want to set the car up properly and be able to take advantage of the additional parts you've added beyond a turbo back exhaust, then you absolutely need ID1050x injectors and AEM340 fuel pump. And at that point you're an ethanol sensor away from picking up another 40whp....so it makes sense to just get the flex fuel too.
* I do NOT recommend a catless exhaust unless you get an external wastegate OR Cobb/ID1050x injectors and an AEM340 fuel pump. Without these mods you chance running out of fuel, leaning out, knock knock boom.
* I will NOT tune any injectors besides Cobb or Injector Dynamics. It's an exercise in futility to try and make a car drive well with crappy injectors.
* If you are running a FMIC, cams, or plan on making 500+ whp then you should plan on going speed density. Speed density is fueling based off the Manifold Pressure (MAP) sensor vice the Mass Air Flow (MAF) sensor. The 10-15 feet of extra piping for FMIC's can cause fueling issues on MAF based fueling. Cams can cause various fueling issues that can only be corrected with speed density. High hp setups require a large MAF housing which ultimately leads to poor idle and cruise fueling due to the large size of the housing and small size of the MAF sensor.
* 02-07 WRX/STi's need an AEM 3.5 bar MAP sensor or Cobb 4 bar MAP sensor to run more than 20psi. The stock MAP sensors on these years can only read to 23psi.
* Fuel Systems
- Stock Turbo on Flex Fuel
* Cobb/ID 1050x injectors + AEM340 Fuel Pump + Cobb Fuel Pressure Regulator
- FP Blue / 20g / GT30 Size Turbos on Flex Fuel
* Cobb/ID 1300x2 injectors + Visconti Tuning Fuel Basket + Walbro525 Fuel Pump + Visconti Tuning Hardwire Kit + Aeromotive or Radium Fuel Pressure Regulator (this setup could be run with 1050x's, AEM340 and hardwire kit but will max out ~400-425 hp, maybe less depending on how cold it gets where you live.....so if you don't want to run out of fuel....mod accordingly)
- FP Green / GT35 Size Turbos on Flex Fuel
* Cobb/ID 1700x2 injectors + Radium Dual Hangar Fuel Basket + 2x Walbro450 Fuel Pumps + DW or I-Wire Fuel Pump Hardwire Kits + Aeromotive or Radium Fuel Pressure Regulator + Full Fuel Lines from fuel tank to engine bay
If you plan on tracking your car or do canyon runs all the time with sustained high g turns, then I would highly recommend adding a Surge Tank to the fuel system to keep it under constant pressure and avoid fuel starvation. Subaru has addressed this issue with the fuel basket on the 08+ cars, but the 2002-2007 WRX's/STi's do not have the basket and will lean out when cornering. This issue is worse the older the car.
TMIC's should only be used for sub 450 hp cars. If you want to make power and keep the charge air temps in check, you need a good FMIC.