I agree with what Sean is saying, which is why I said, "if there is a 17.5 class, I would run that".

If 13.5 is the slowest class they run, go with the 13.5 and adjust either your esc current limiter or adjust your radios high point. That way you can run the faster motor with less power and work your way up to more power the better you get.

Thanks guys.