I am having trouble deciding what to get, what diameter I need, whats best for Hp and nice sound as well. Ive been looking at skunk2 but the one that fits my car is 3" and a buddy who builds Subaru says thats too big but the 50 and 60mm say they don't fit the Si only DX. The engine is stock other than an SRI i just put on from AEM. I ordered a CAI as well but i'm nervous to put it on for hydro lock. This is my first MOD car ever and I'm losing my mind trying to figure out what to do.