Curious about this myself, just got my son an 03 dt125r and had to ride it for 30 miles back home today. i found it really gutless.
the exhaust sounds really choked so i would imagine a freer breathing pipe would help. i have aslo heard about doing an inlet tract mod by the reeds not sure how much difference it will make. as for the speedo mod that is only going to make any difference when the road speed is 60mph+ so will not liberate anymore revs.
i am still searching the net for the answer. if i find anything i will post a link or explanantion here
