ir_fuel, since you keep on being so skeptical about this (despite having been referred numerous times to the US boards for a search...) why don't you buy:
a CAI
headers
hi-flow cats
full exhaust
and do a before-after dyno runs, for each of these, see how many hp you gain ?
btw what I meant was that most (not saying all) ebay unbranded "performance" tat is so badly designed you'll most probably lose hp instead of making any
Look at those headers ffs!