Originally Posted by RallySport Direct
For any 08+ WRX and STi any intake changes require a tune. We did testing on this a few years ago when trying out different stuff on 08+ cars and ran into it the sensitivity issue of these cars and air flow.
This dyno plot shows the AFR curve, however we ended up having to richen the car out to correct for the change in flow when we did a drop in. I dont remember exactly the #'s but it was along the line of .5-.75:1 lean out when going from OEM to drop in high flow filter.
So in a nut shell, stick with OEM air filter and airbox unless you plan on tuning for it.
Curios why, if you know this, you don't always correct the vendors on your site when they tell people that they don't need to tune specific intakes. Might want to look into that so people don't make their engines go pop!