[EJ257]

I would NOT replace it with a TD04 again.

The advice of a used STI takeoff VFXX is a good one; you should be able to get one of those relatively inexpensively. While you don't NEED injectors / pump / boost controller for an STI takeoff turbo, you're going to be getting custom calibration anyway, so now is the time to do it. Any VF turbo is going to basically max out your fuel system, so this would give you some safety margin, and the ability to run E85 in the future. You want ID1050X injectors, if you decide to upgrade. You will absolutely want to have an aftermarket turbo inlet (e.g., Perrin) available when you do the swap, as the OE inlet is notorious for tearing during turbo swaps. If you decide you don't want to use it, you can always resell it, but have it available for the install in case it becomes mandatory.

The other option which I think is worth considering, is an 18G turbo. For example, the Blouch 18G-XT (link) is a great DD turbo on the 2.5L platform (you would probably want to opt for the 8cm housing). While peak boost comes on later in the RPM range than a VFXX, the increased airflow of the Blouch unit means the powerband doesn't really shift much, and it holds power a lot better towards redline. Coming from a TD04, you'll fall in love with your car all over again with the Blouch.

I think a well-built 18G setup (EL manifold, EWG, TGV deletes) is about ideal on a 2.5L for that serves as both DD/weekend duty.

 

[EJ257]

The blouch is a bit outta my budget. Going the vf route seems to be the way to go money wise. Can you school on what an ewg and tgv delete is?

If you're shopping the used market for an STI takeoff turbo, you may be able to find an 18G too. You're going to pay a bit more of a premium on it because the supply is lower, but don't think you can only get them for $1250. You might be looking at $800 instead of $500 for a similar mileage unit. That $300 is money well spent in this regard, if you're already buying supporting modifications that can handle either.

Out of your budget (based on your reply), but put simply...

On the hot side of your turbo, you have both a turbine wheel and a wastegate. The wastegate is used to divert exhaust gases away from the turbine to regulate boost pressure (without a wastegate, you would just continue to build boost pressure as the exhaust gases continued to flow). An EWG "replaces" the turbo housing wastegate (it's either welded shut or held shut via a bracket) with a wastegate that's pre-turbo. The benefit to this is you can mount a larger wastegate (since you're not limited to the turbo hotside housing) and it helps reduce exhaust gas back pressure since there isn't a build-up of exhaust gases piling up on the turbine / wastegate in the housing; this equates to better boost control and more power due to higher volumetric efficiency.

TGVs are emission control devices between the intake manifold and the engine block. There are flappers that open and close. TGV deletes get rid of that restriction (even with the flappers fully "open" they obstruct airflow due to their existence). By removing that restriction, you make it easier to get more air into the engine. The more airflow you're able to get into / out of the engine, the more power you make; that's the whole concept behind forced induction (you're stuffing more air into the engine with either a supercharger or turbocharger).

 

[EJ257]

Now on the tgv delete would the be something I can do. Or does it require machine work or tig welding?

It doesn't require welding. A port & polish job is recommended, but not required.

You can make it as complicated as you'd like. On the cheap, companies like KSTech sell blockoff plates:
Weldless TGV Delete Kit - '02 thru '06/ '07 Subaru - KSTech

You might be able to find a set of TGVs already deleted on the used market.

Companies like IAG sell sets that are plug and play:
https://www.iagperformance.com/IAG-...GV-Deletes-02-07-WRX-FXT-p/iag-afd-3000sl.htm

Doing TGVs at this time would help with other installs (e.g., turbo, inlet, injectors), so now would be a good time to do it.

Will the stock internals hang with a turbo upgrade and some of these other mods you recommend ?

Assuming the engine is in good health (a compression and leakdown test will tell you that), this setup shouldn't push your car to the "not if, but when" failure point. The further you are from stock, the greater your chances of mechanical failure, but an 18G is a relatively moderate turbo upgrade, and if you have a good tune, I would expect the car to last for a while.