Intake Systems for 2002-2007 WRX/STi
Tech Note: "Short ram" intakes dispense with the factory intake ducting completely, in the interest of the shortest possible air path. They generally give good power numbers, and since they're positioned high up in the engine bay, water ingestion is not a problem.
On the other hand, your factory intake ducting is excellent at scooping cool, fresh air into the intake. The short rams suck warmer underhood air. This probably isn't a big deal once the car is up to speed, but after idling at a light on a hot day, you may see elevated intake temps.
All the intakes we sell have properly sized MAF housings that should NOT change your air/fuel readings. They all flow about the same; we observed five hp at the wheels using a short ram system on an otherwise stock 2.0 WRX.