Scenario 4: Time to go built shortblock?
Airflow range: 320 ~ 360g/s (44 ~ 49lb/min) (627 ~ 700cfm)
Typical power outputs: 340 ~ 400whp
This is the typical range for EJ255s with the following turbos, listed roughly in order of potential:
Blouch Dom 1.0XT
Shortblock: This is really well beyond what the stock pistons are going to deal with. A health stock bottom-end should be okay at this point but the pistons are really out of their depth.
Heads: Stock ports and cams are not yet the choke point but you would gain with a TGV-delete.
Clutch: All models require a clutch upgrade at this point, but disk-type clutches with streetable spring pressures are fine.
Transmission: Subaru 5MT is a question here. Many fail, some don't. If you're careful how you drive you may get away with this. If you're the launch-control kind of driver you may break things.
Intake: Stock MAF tube critical at this point as it can read up to about 380g/s with typical scaling. While there are turbos in this size range that can fit the stock intake it's probably the time to go aftermarket intake and big MAF.
Intercooler: Most people running in this power bracket have a FMIC fitted. While it's possible to run a very good TMIC like the Process West item you will probably do better with a FMIC. Note there are very few flange outlet turbos in this size range.
Injectors: Recommend 850cc or larger.
Pump: Aftermarket pump mandatory.
EGBP turbine: MHI-based turbos need an 8cm2 housing minimum, and consider 10cm2. With the Garretts stick with the .70 A/R housings and all will be well.
EGBP exhaust: High-flow catted or catless downpipe mandatory. Headers will add solid gains on these larger turbos, and the stock manifolds would probably be a serious choke point. Catback exhaust also really needed at this point unless you want to leave significant power on the table.
Other: 3-port EBCS will add control authority and help smooth boost response. You may even consider a hybrid system with both an EBCS and MBC. Stage III tune required at this point, pro-tune, dyno-tune or e-tune, with injector and / or MAF scaling to do they all cost $ unless you have the chops. This is also the point where many people will choose to go to a rotated setup to avoid stuffing a big intake under the intake manifold, fouling the TGVs etc. There are still good choices in the stock-location sector however.
A lot of people are fitting catch cans or air-oil separators along with mods like these as blow-by can and does become an issue.
Scenario 5: I just got divorced and I want to go crazy
Suggestions please, in the range of MD321V, Dom 1.5R, 2.0XT etc. 400 ~ 450whp range.
Shortblock: Upgrade pistons are mandatory, forged rods probably are too. Head studs a good idea. Other suggestions welcome.
Heads: Stock ports are not yet the choke point but you would gain with a TGV-delete. It might be time to consider cams.
Clutch: Shop 6MT clutches to match your new...
Transmission: This is really 6MT territory now unless you like the sound of straight-cut gears and insist the 5MT has better ratios for drag racing.
Injectors: Just get the ID1000s, you will need them.
Pump: Available drop-in pump? Think booster pump, surge tank, parallel pump set-up etc.
Other: 3-port EBCS mandatory. You may even consider a hybrid system with both an EBCS and MBC. Stage III tune required at this point, pro-tune, dyno-tune or e-tune, with injector and / or MAF scaling to do they all cost $ unless you have the chops. This is also the point where many people will choose to go to a rotated setup to avoid stuffing a big intake under the intake manifold, fouling the TGVs etc. There are still good choices in the stock-location sector but you're being stubborn now.
Catch cans or air-oil separators are probably a must-have as blow-by can and does become an issue.
* STi fitment turbo, doesn’t fit the stock TMIC, the typical AVO / Perrin aftermarket TMICs or straight bolt-on FMIC kits. Check fitment.
** Non-standard uppipe and discharge fittings. You will need exhaust components to match the turbo, might be available as a kit, might not. Quite likely that the turbo does not fit into the stock location and/or the intake pipe cannot be fitted under the intake manifold.