on a stock tune, you will lose power in the top end if you change the intake out. (keeping that simple haha)
Pick one of these options:
1. You need someone to rescale your MAF (mass airflow sensor) for you (super simple w/tactrix) if you're not looking for much power, but want your car to run properly.
2. If you're looking to get a decent power upgrade with it, you need a stage1 tune, Walbro 255lph high flow fuel pump, and you need to rescale your MAF in that stage1 tune. 08+ stock fuel pumps are junk and can barely support stock boost/timing levels above 5500rpm. In fact, they will occasionally cause small amounts of knock in that rpm range due to lack of fuel on a STOCK tune haha... Must be the same pump they use in the N/A impreza. Stock tune is super crappy if you catch my drift.
3. You can take the intake off asap, because without a tune you're running lean.
hope this helps
-----Added 8/22/2009 at 07:51:54-----
also, XPT tunes are nice, but he usually tunes for "no knock" instead of A/F and "no knock" so his A/F's tend to run in the high 11's and low 12's under boost. On the corn oil we have here in maine, those are too high. You need to be down in the 10.6ish range under boost. XPT tunes are a great place to start, then have someone tune those A/Fs down for Open Loop.