You can run 550's down to 12 turns. It cant run brushless motors. Here's a nice upgrade motor...............try it on 14 cells(16.8) it should run nicely.

http://www3.towerhobbies.com/cgi-bin...?&I=LXWR56&P=7

Heres the one with the most power and top end, this on 14 cells is all your gonna get out of a villain.

http://www.rcplanet.com/ProductDetai...RI9243&click=3

Oh, the 12-17t motors must have traxxas connectors................NOT molex/tamiya [:'(]