The pipe thats on your MBX will be fine for just bashing around, if you get more into racing the polished one piece pipe is a lot better, it wont come apart and gives higher performance then stock. CVEC pipes (dual outlet pipes) arent race legal and dont give any better performance and have heard they suck (at least on .21's) from people that waisted the money on them. Your .25 engine is basically the same as the .21 so any .21 accesories should work.