I have a APS CAI that came with the car when I bought it. Can hardly hear it. Not sure about performance since I haven't done dyno yet will let you know next week when I get it tuned.

using the Perth-WRX mobile app

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02STi - Vipec, Oval Varex, APS CAI with K&N Filter, Walbro 255L, 53MM Koyorad & STD Coilover

19.5psi tune 271.6HP@6000 351.3NM@4700