http://forums.evolutionm.net/showthread.php?t=171218
^story about a cheapo filter that blows, it is marketed on ebay as an hks-type filter.

The basic story:
"This intake is the worst thing we have ever seen on a car. I cannot stress enough how badly this thing works. The problem lies within the filter and maf adaptor, not so much the intake pipe. We had a 2005 come in with some nasty turbo kit on it and this intake (just the filter and adaptor part, it had an intake pipe for the turbo kit). It was a brand new car with less than 2k miles and it was dynoing something like 255 whp on 20 lbs of boost with a GT35R. The karman readings were pushing close to 2900 hz (which is around the 500+ whp range). We removed the filter and adaptor and the karman counts dropped under 1600, had to be totally retuned and the horsepower went up to around 320+. We then put our standard intake adaptor and K&N filter on it and it worked perfectly.

Just wanted to throw that story in there just to overstress what Al said about this piece. IF YOU HAVE IT ON YOUR CAR, TAKE IT OFF IMMEDIATLY and get your car retuned!!!!!!"