i m using castle 7700kv system. on my tt-01 gear 5:1. 0-400M kick FW-05 2 speed gas car no problem. but too fast can't turn. on my ta-05. gear 7:1. still fast and more fun. i m using 7.2v nimh..check it out www.castlecreations.com.. it cost me about $400 us.