When I converted my revo I was running a 9xl with a 4 cell lipo and it ran like a champ. Right now Im running a 7xl but i think im bout to go back to my 9xl cuz the 7xl seems to run to hot. Be sure if you get a 9xl you get some new tires cuz it will tear em right off. I would suggest bad lands cuz i aint had no problems with mine yet. :P