Here's a good link on Intakes from the Unabomber.Most major Subaru tuners agree that the stock intake is adequate to power levels in the 400HP range. It also has the following advantages:
- The standard air scoop is mounted high in the engine bay. This makes it resistant to ingress of water. The design of the fender snorkel helps to remove any water that is drawn in by this scoop.
- Air drawn in is cool, since the air comes from the edge of the engine bay, and at speed, all air will be drawn from outside.
- The standard system is quiet since the resonator in the fender helps filter out noise from the air flow.
- The stock ECU is calibrated to work perfectly with the stock intake system.