I have a stock Impreza 2.5RS..

Any suggestions?

not much..probably 5hp, not enough to notice. Also the sound of the engine when accelerating will change, in a good way IMO.;)

stevo

Does an air filter really give 5hp of power? I mean if you calculate hp/$. 5hp/$50 = 1hp/$10 is pretty good. I thought the main advantage was if you had other mods or if you kept the filter clean.

I'm a little skeptical about the 5HP increase. That seems like a lot for just changing out the filter.
I agree it will do more for the sound of the engine than the actual power you can feel with your butt dyno.

Changing the air filter will have little noticable change on a normaly asperated car. There can be a signifigant change with carborated engines. Mostly it is a starting point, help the car breath better and other mods will make a bigger difference, or at least that is what they tell me. I had a K&N on my old Jeep, gave it more kick, and am planing on replacing the air filter in my rex with a K&N, they seem to work well for me, plus you never have to replace them.

i have the ITG filter and it fits perfectly. Sounds great too along with my silencer removal.

I haven't noticed a huge difference in car response, but i did put it in just after my break-in period.

Also had a K&N in my GTP before I sold it. It had slightly better response, but not a huge one. :)

~V

Carburated cars you will see a difference.

On a N/A subaru, not on your life. At best, 1Hp.

WRX, shiv has dyno numbers to show it deos not add hp, again, at most, 1-2HP.

--kC

not much..probably 5hp, No way. More like 1hp.

IIRC the dyno charts for ITG showed that the stock filters are quite high-flowing. In fact, when new, they were better than the K&N and ITG. However, over time, the factory filter degraded fairly quickly, and ITG soon was the top filter for any extended period.
So from that you could put in an ITG and get good results for a long, long time, or you can get great performance from the stock filter for a short period of time and then not-so-great, or you could just buy a bunch of stock filters and replace them at shorter than typical intervals.

It is a start to future mods, or a washable filter removes the need to buy replacement filters at the specified intervals.

Installing the K&N into my then-stock RS removed the 4K flatspot, and that in itself was worth the money. It'll flow somewhat better, but it's not magical. It's a start.