I did this to my turbo last September and if you want really cold (ourside) air and to hear the turbo swoosh and the blow off valve pop then take a look!
I cut a 2-1/2" hole through the firewall, cut and added a screen to the black plastic cover, added a cone K&N filter under the cover and ran it straight to the turbo inlet with 2-1/2" tubing and 90-degree elbows. All the sounds that you could want and nothing but fresh outside air! BTW, with this setup you DO NOT want to remove the rubber seal at the back of the hood! Too much heat from the engine makes its way to the intake!
However, I can't report any great gains in HP. The track times before and after only netted about .1 seconds in the 1/8 mile. This is with the exhaust system changed to a 3" hi-flo cat, 3" straight pipe into a 3" in to twin 2-1/4" out glass-pack muffler. Again, it sounds great. Deep throaty roar, not high-pitched like a ricer!