I believe it stands for hot film meter, but i'm not too sure. i know it goes along with the intake and that it is a costly upgrade, but from what i read it brings about many hp along with a cold air intake. i'm in the market for an ecis cold air cuz i'm not enjoying my ractive rig, which i believe is taking away hp- could anyone verify that a cheap intake will take away? (it's not cold air for one thing, but it does have a shield around the cone) well thanks for all your help guys, also could anyone tell me how to post pictures, i'd love to share some pics of my car with you guys. thanks in advance.