first of all as someone who's been "around the WRX block" let me say that there's a tab called "search" on the upper right of your screen that can probably get you answers to all your questions...next time try it first.

Intake mods are not necessary until you start getting over 350+hp at the crank. The stock intake flows plenty of air for the stock turbo as well as any of the VF series. They won't give you any more power and will usually throw off your ECU. SOME intakes can be tuned. For example Cobb has maps for the Injen intake. It doesn't give you any benefits, but if you want a noisemaker then you can have it without screwing up your air:fuel.

The silencer is a piece of plastic in your fender that air flows through. Its a pipe with a big bulb on it that helps tune out certain frequencies of "motor whistle". It also serves as a water trap. Some people cut off the bulb and seal the hole or replace the piece with a bypass that doesn' have the bulb on it. Yet others simply remove the piece and the snorkel that ducts air from the front of the car into the intake alltogether. All this does is make more noise. It offers no performance benefits whatsoever, and although the difference it relatively small, it also slightly increases the temperature of the air coming into your motor and removes the "ram-air" effect that the snorkel provides. These effects are VERY small, and unless you're measuring in .01's of a second...or even .001's, you won't be able to see the loss.

Intake mods are 99% useless noisemakers. Unless you're putting in a Garrett turbo, or a PE20...or some other monster snail, you don't need one.

 

Links to threads concerning cold air intakes.

--
0==WW==0
"…axles of evil…" - george w. bush