Use the search function, it really does work.
What kind of motor/esc are you using? Also, what kind of track? (fast, tech, etc) And are you very smooth with the throttle/brakes or are you more of a smash and bash driver on the throttle?
A cap just smoothes out voltage spikes from the motor to the esc, you should be fine with a normal 16v 4700uf cap.