DO NOT GET A CAI FOR A WRX. This topic has been beaten to death at
www.nasioc.com. The MAF sensor gets all screwed up and it will kill your car. The stock intake is good till roughly 400 horsepower, but at about 350 maybe a bit more the tranny and engine internals will start to let go. Get a downpipe, uppipe and engine manangement and you will be at around 285 or 290 horsepower at the crank and will have a much more fun car to drive. I am at stage two, which is downpipe and engine management and have about 280 horsepower(extremely smooth power curve with no turbo lag), when I get my uppipe and cat back exhaust it should free up a few more hp. Go to
www.nasioc.com and search around there, it is the best subaru resource in the world.