Originally Posted by Henry H
Is that so? I'll have to look into that. Any links on this?
It is very "so". You can improve gas mileage and power output with a good tune, BUT only if you have the supporting hardware to allow for increased efficiency. Good EL headers (TWE is really the only option aside from some one-off fabrication), an intake and a tune could potentially get you +20 ft/lbs peak and maybe +10 hp at redline, but the biggest gains would be in area under the tq/curve especially under 4k rpm. My highway went up a very solid and repeatable 2mpg per tank.
without any bolt-ons a tune won't net you any milage increase, it's already pushed past the limit from the factory. A tune on a compltetly stock engine can improve driveability (most noticeable with manual transmission) and reduce/eliminate the knock that is present on even 93oct gas.
The hardware to get the described gains will cost ~$1000 plus labor and a good, thorough dyno tune is usually $200+
like everyone has said, extracting more power is possible but cost amounts of $ that most who buy a 2.5i are not willing to spend.
You could make 300+ hp n/a but it will cost something like $10,000 or you could make 200hp n/a and it could cost something like $1500
Also, ImprezaJohn, try not to get too caught up in the internet dick measuring contests that often erupt on here. lots of no so good info, but its easy to weed out with a little follow-up research.