[AWDFTW]

It would be easier and more cost effective to trade it on an XT or H6 model.

You have to upgrade....well, everything to do it right and not go kaboom. It'd cost more than the difference between vehicles.

 

[rasterman]

Cheapest is trading it in.

Next cheapest is to swap out the entire engine from a crashed WRX- that is actually not bad; nearly everything is a direct bolt up. You can sell off the original engine to recoup costs. You will be able to find specialists who have done this.

You can add a supercharger, cardoc has a thread on this board detailing his project on this path. Not remotely for the faint of heart.

 

[mike552]

+1 for Supercharging. You can run it on low boost and still have a reliable vehicle. Keep in mind, though, that (IMO & others') the real weakness in the 2.5i is the head gaskets. So, yes you can supercharge, but unless you keep it under 3psi, know that you will soon probably develop a leak at the head gaskets, at which point you will need to re-surface the heads and re-install them with "turbo" gaskets. This sounds like a costly and time consuming job, but it really isn't that bad (or expensive) if you can get someone to do it right. Who knows, your head gaskets may be sweating already so it may be better to get them done first before you attempt a forced air induction retrofit.

FWIW, I am planning to Supercharge right after the winter. I would've done it already but I haven't been able to get my hands on a good, relatively inexpensive short-snout M45 or M67.