The best CDI box?

Honestly a CDI box isn't going to do much for you, the stock one works just fine. If you are still stuck on getting one I have several high rev boxes available.

An exhaust isn't going to do much for you either except make more noise. Again I have stainless pipe / aluminum can exhausts available which might improve the top end a bit as they are sized for 125cc engines but might hurt the low end a little.

Basically keep in mind you are dealing with a toy. You are trying to make it do things it wasn't designed to do so look at it with a big picture scope and then break it down in to manageable chunks. Part of breaking it down will include determining what level of performance and the dollars you want to allocate to it. If you want an immediate improvement in how fast the bike is I would suggest swapping the engine out for a good quality knockoff suck as a Jialing (GPX) or Lifan (once again I can help you out there as well). Of course once you have a faster bike you will make it do stuff that the OEM frame, suspension & wheels can't handle (there I am again)... So you have a chicken or the egg situation.

Or you can buy a really nice pre-built pit bike and not have to worry about which piece comes first.

pat "at" pitvipermx "dot" com will work