If you don't have a tuned pipe get one, The next thing is a slide carburetor.
Both of these items will cost almost as much as a new engine. I can see the need for a pipe but not for a slide carb at $50+.
[HPI]RS4SS;
I dont know why, but my friend's RTR3 beat me in drag......
Try removing the restricter that goes into the muffler/pipe, then re-adjust your fuel mixture if nesessary.