There are a lot of problems associated with the design of a proper "ram air" system, which is essentially what you are talking about. Number one problem is that they tend to create so much turbulence that they actually result in a decrease in performance.
A standard cold air intake (CAI) is most likely the way to go. Take a look over at
www.re-speed.com and check out their modified radiator mount. This comes with an opening designed to be used in conjunction with a CAI system. They are also working on an air cleaner housing that has many improvements, along with being CAI friendly.
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