It depends how fast and how powerful you want your go kart to be. For faster acceleration, you'll need a stronger motor. Seems like you will need a motor rated for few hp to be competitive enough. 1 hp = 745.7 watt. You will need motor with rating of several thousand watts. Try ask in go-kart thread (if any )

---

Added on June 10, 2009, 10:45 pmI have reach the final stage of circuit prototyping, and will be moving on the the next step, which is PCB fabrication. Currently stuck on trace sizing.    How wide should it be, for a 6v, 6A (typical) and 8A (peak) current?   I googled around, and there are several version. I like to hear from someone who has experience it, if any.

Here's few sneak peek of the electronics:


The 2nd picture maybe familiar to some RC fan.