The cone shaped thingy is an air intake silincer. primarily used to quiet the incoming air for noise purposes. Removing it should make more power. Not sure how much, on a mustang it makes a pretty noticable diff. Hope this helps!
if you truck has a ressonator take it off plug up the hole and you get nice sound to. did that to my 2.3 tempo and ended up tearing the muffler out the next day (accidently bottomed out) and it sounded like a beefed up honda after that. and yes i do blieve youll see quite a difference. may not feel it in high geer but will deffinetly get lots more torque that way.