Just replaced my standard paper filter with a new Green cotton job from scoobysport and feel the car is now "less eager" at lower revs.
Once the revs are up in the 4500-6500 range it feels better than before, but this lacking feel low down has just got me wondering if the ecu is adjusting the fuel mix properly.
I also seem to be getting more miles to the tank than before also.
Has anyone else noticed this?
(I drive an STI8)

 

Can't comment but didn't notice any real change when fitting mine to my MY99...

I would be a bit more concerned at the fact your fuel consumption is improving as this may point the more serious fact that your car is potentially running lean

 

I bought a dump valve of a chap in Nottingham, and he said the same thing.. Improved fuel consumption with the cotton filter, he recon'd 30mpg from a 02 WRX.

 

Have you reset the ECU after fitting?

 

The fuelling is determined by the air that flows past the Mass Air Flow sensor and this sits in the air stream after the filter. A better air filter can allow more air through and can allow better acceleration of the air, towards the turbo, but it cannot change the ratio of fuel added to the engine for a given air flow. This is preset in the maps.

It won't give you 30mpg.