The '05 also has a TPS (throttle position sensor) on the carb so that might not just hook up without some electrical mods.

They also added several gussetts and welds to the '05 frames in addition to what others have said here (37mm carb, new cams/valves, extra clutch plate)

 

why is your cylinder head bad?no difference than a 03-04 head.i say save your money get some cams and do the drz-e base gasket.

 

Listen, my friends uncle has an 05 z and mine is an 04. His MIGHT be about 1 mph faster then mine there is really no difference at all in speed or acceleration, BUT the throttle is smoother, due to the clutch changes the clutch is better and more responsive, and the suspension is much better especially for jumping

 

I don't know about that. I rode an '04 and while it may not be any faster at the top end the '05 is quicker through the gears. The '04 seemed to have a bit more "grunt" down low while the '05 has virtually all that same low end with a much bigger mid-range hit. The redesign of the cam/valves has more to do with it than the TPS does. The TPS is basically a better way to acheive optimum efficiency.