Intake Silencer Delete (02-07 WRX/STI - not sure about other models)
The intake silencer sits on the right hand side, in the fender area. There are 3 bolts holding the intake silencer on. One can be accessed via the engine bay, the other two sit behind the front bumper - one down low, one up high near the engine bay bolt. You can access this through the fender well if you detach the plastic guard. Taking off front bumper makes the removal easiest. Unbolt, remove.
Some people leave it as-is (gaping hole), others saw off the silencer and block off the hole to fashion their own elbow, you can also apparently buy an aftermarket elbow so you can keep the OEM piece intact.
Gains? None. Arguably a tiny gain when combined with drop-in panel filter (e.g. K&N). Most seem to do it for the increased turbo noise it provides. Plus.. weight reduction?