It would be more likely that the additional back pressure is doing that. It seems you have based your assumption that there is less restriction in the new exhaust on a larger header diameter and a shorter silencer of the same internal design as the '07. The '08 muffler is not at all the same. http://www.motocrossactionmag.com/ME2/dirmod.asp?sid=&nm=&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=3C64793A1A204AF0AF3E7ECC2A3CD20C Besides, it doesn't work like that. The ongoing myth that back pressure created by any sort of exhaust restriction is of some benefit to a 4-stroke continues to amuse me. The 07 had great low end power and the 08 exhaust system is redesigned so I was thinking this had to be the reason for the lack of low end power on the 08. Thanks for the explanation.