The aftermarket intake inlet can only increase your HP numbers if your present set up is a restriction. Though I'm not sure of the 99-04 inlet abilities with a K$N filter in place I am VERY aware of the abilties of the K$N filter and stock inlet/box on my 88. My 88 is a fairly heavily modded 302/306 N/A setup making in the region of 300RWHP...yet the inlet and box from ford flows MORE than enough, with an aftermarket filter to fulfill the needes of my motor. In my case going to an aftermarket "CAI" would yeild no gain..there is not a need for more air as the car is. Now the fatory systems draw air from the same location as the "CAI"'s do so with a K$N filter in place I'm willing to bet the car is able to draw enough air from the stock box to meet the abilities of the TB and the heads to flow. As for Temp drop..the CAI's will not create a temp decrease in the time the air is drawn from the fender..to the TB regardless of material it's made of. I will note the CAI's in aluminum look incredible..if they did not F-up my MAF A/F reading (found the bend in the inlet on the fox style was creating air turbulance in the maf reading at higher rpm) I would definately be running one...I love the shiney stuff. The wifes 04 is as stock as stock can be..I will likely go the route of the K$N eventually and will report should I see any "felt gain".