ya, its just tough to tell cause the plastic is identical, but if you look at everything else its all new. the new frame and swingarm dropped 5lbs from the 04 and the new motor is 4lbs lighter than the 04, plus is alittle faster. all new suspension also and Renthal bars stock. the 04 was a great bike though. i’d say it was near the top of the heap but the 05 just blew away everything else out when it came out (even though the ktm has alittle more power, but overall the YZ is a better bike).
http://www.transworldmotocross.com/mx/features/article/0,13190,1048514,00.html