does a induction kit improve performance by much or at all and which one is best for 04 sti and what actually does it do help please

 

Forget the induction kit, get yourself a good panel filter and exhaust. The two should complement each other.

K&N, STi, etc there are loads out there. I have a K&N on my 03 STi and a TSL system with Group N back box, sounds awesome