l am think about buying a subaru impreza wrx sti anywhere from the year 2002-2005, and im think about buying a turbo kit. l am wondering when l do buy a turbo kit what system l should buy and what other parts do l need?

We only got the ST l from 04 so that is all l am familiar with but any turbo bigger than a big 16G or about 39lb/min turbo will also need higher flowing injectors & a upgraded fuel pump. As far as what u need that is it. You would benefit from a bigger top mount or a front mount intercooler & a better turbo inlet. If u plan on running more than 350 WHIP then l would look into a better intake as well. You should also think about a less restrictive exhaust system to get the most out of the turbo. l would check out Blouch Turbos or Deadbolt Turbos for many Subaru options. As far as other mods the best person to ask is ur tuner. Each tuner has different styles & will recommend different injectors & what not so u should talk to him about ur goals with the car.

you do realize the sti is already turbo dont you? haha.

there r two routes.
1. upgrad to a better set up but still keep it looking stock.
2. upgrade to a bigger turbo upgrade all parts under the hood.
you can get an upgraded turbo from many suppliers such as Power interprise, Zero Sports, Greddy, HKS. they all offer turbos that r bolt up kits, & still use most of the OEM parts from the original turbo, & give a good amount of power & spool up quicker then the stock turbo.With these set ups u can use a OEM STi top mount, but it would be a good idea to upgrade to bigger injectors 500cc injectors would be good, & a fuel pump, an STi fuel pump could do good but u can always upgrade.
You can upgrade to a bigger turbo for powers over 400 but u will need to use bigger injectors, more fuel, front mount intercooler, upgraded intake, & exhaust.
This all depends on what u really want to do & how much u really want to spend.