From what I have been reading with the 05+ mustangs, replacing the shorties, doesn't give you much HP's that is worth the money. LT's I have read give around 30 HP's. But the problem with the LT's is that there are not street legal because of smog laws. This even goes for catback exhaust. I remember when that mod would give a decent output, but now, it may gain 1hp. Basically people just get the axleback and is more for the sound than anything.