I was wondering what the difference between the EJ25 (2.5l non-sti motor) and the EJ257 (2.5l STi motor) was so i did some searching but couldnt find anything. One of my friends told me that they were almost the same accept the sti motor has a turbo the the other one is n/a. If this is true im going to get a 98 impreza in a few weeks.

The EJ25 is naturally aspirated, the STI engine is turbo charged.
The STI engine also has an entirely different block(from my understanding), valves, pistons and just about everything else.
Don't get a '98, rather get a '99, the '98's are notorious for developing head gasket problems.

Same basic shape; internally VERY different engine blocks.

Please do plenty of resreach if you're thinking of slapping a turbo on an N/A 2.5L Subaru motor. Most end up with "relaibility issues" after the owner fails to compensate for the N/A motors' much higher compression ratios.

Damn, thats too bad. Im trying to get into rally racing with my friends and so i want an awd car.
I was going to try to turn the 2.5l N/A impreza motor into a sti engine but now im thinking of the 2.2l ej22t from the 92-94 legasy turbo since its already turbo and everything. Think this would be a better idea?

The STi engine has a semi-closed deck block, the N/A engine is open deck. But still, replace the pistons/rings on the N/A and you've got a motor that will stand up to ~300 hp

Yeah, the N/A 2.5 is no slouch, so don't discount it right away.