I am looking to do some mods. to my son's ttr125. Research tells me that the best thing I can do is open the air box and go with an aftermarket exhaust. Which one? I have looked at several web sites and charts and I still can't determine that one model stands out over the rest. Will an aftermarket exhaust "Really" make that much differance? He is racing in the youth events at the enduro and hare scrambles and I would like to hop the bike up some. I need some advice based on experiance, not from a marketing department. If the add-on want put some kick into the bike, why spend $300?