The intervals for filter cleaning mainly depends on the conditions the car is driven on, For me the real question here cost, power gains and installation and cleaning procedure. These are numbers from other posts on the forum:
K&N drop ins + HPS tubes= aronund 13 whp costs around 200, easy installation and cleaning.
Stillen G3's= 18 whp costs around 500, mods to install, bumper removal to install and clean.
For me is a 5 whp difference, not worth the money or the hastle, this is my personal opinion.
