simple newbie question
 

what is the difference between the 7xl and 8xl cuz i run a short track and need good aceleration for coming out of the corners but for bashing i would like 45+ would u still recomend the 7xl

The 7xl has 7 turns, the 8xl has 8 turns. Less turns equals more rpm/volt and more current flow. So, yes, the 7XL will be faster, but will heat up more, and have reduced runtime.

what kind of run time will i get with ib 4200

MAYBE 15 minutes or so.