Hi,
I bought the cone K&N for $100CDN ($70US), and running without any ram-air setup, all I noticed was louder noise, more of a whistling/sucking sound, and a little better throttle response.
I got fed up with the excess noise, so I put a cover over the filter (from a plastic bottle my bro got that was an exact fit over the filter), and made a ram-air setup using some tubing I found near my clothes dryer. Also, I was lookin around in a Mustang junk store, and managed to pickup a scoop (similar to the one in March's RAM-AIR kit) for $10CDN ($7US).
So all in all, I spent about $10 to create a basic ram-air setup and although it's hard to feel 4-5hp gains, there is a difference then running with stock filter setup.
I don't know if it's worth spending extra for a cold-air/ram-air setup, when you can spend fraction less and create your own with a few supplies from a plumbing/housing store.
Bye!
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Gautam N. Lad
http://www.cubicdesign.com
http://www.cubicdesign.com/mustang/