Just passed the 1000 mark on my PPP'ed WRX and I'm pretty impressed - wondered if I should replace the standard air filter for a replacement panel filter from K&N or Pipercross. Don't want to go to the trouble/warranty risks of an induction kit but wonder if I will notice any difference just replacing the standard unit?

Also, would a de-cat invalidate my warranty? It's just that the car seems a little sluggish under 3.5 rpm (although its still quite tight).


thx