Before making your mini really fast, I'd make its frame stronger, its stock suspension better and its front end wider. If you turn a 2 stroke mini into a rocket without these improvements, your young rider "will get" seriously hurt. Many people upgrade performance, run out of dollars from frame / suspension improvements and they next they know, the young rider has a broken pelvic bone, broken arm, or their modified broken mini sits in the corner of their garage - because they have no remaining dollars to fix it.
To make the frame better, install gussets. This can be done by your local welder guy. For pictures of minis that have gussets, surf the pictures within:
To make its rear Swing Arm better, replace it with a square tube construction Swing Arm. For pictures, surf:
Shocks is the next area to upgrade. Many install Works Shocks. But for a few more dollars, one can install Elka "adjustable" shocks. For good prices on Elka shocks, contact Ed at http://www.lucky7racing.us/
To widen the front, some people install wheel spacers. For fast trail rides, I'd highly recommend 3+ A-Arms on the front. Wider A-Arms creates less stress on its stock bushings and and wheel bearings. If wondering, we installed 1.5" wheel spacers on our Trail Riding Pred-90. Next time, I'd install 3" wider A-Arms. Regardless, my son hasn't tipped his Pred-90 since making its front end wider.
Adding more performance on its stock system is a serious accident waiting to happen... Hope these ideas and emphasis on making the its frame & suspension better helps.