[othello]

Well ... A123 batteries should be able to constantly ouput 2.2A for 1 hour (A123 -> 2300mAh). You are looking for 20 minutes runtime: 1/3 of 60 minutes (1h). Therefore your average amp draw should not exceed 2.2A x 3 = 6.6A. Otherwise you won't run for 20 minutes.

A123 batteries will hold around 3-3.1V under a lighter load. As you are using 6 cells (3V x 6s = 18V) your average voltage will be around 18V (i would expect it to be somewhat higher). When you multiply average Amp draw with your average voltage you get your average power -> 6,6A x 18V = 118,8 Watt. As i said, that is about 1/3 of what my heavier buggy needed.

But this really depends on how hard you will drive your car, track type and so many other variables. Report back when you finished your maiden run ;-)