[Al Skierkiewicz]

Eric,
Four motors or six doesn't matter if you don't get the reduction right to put the motors in a correct spot on their respective curves. A car battery will certainly let you run longer but you will be stressing the other components if you plan to run for a greater length of time then two or three minutes. Many teams are running very close to trip temperature on the breakers in a two minute match. You might have to redesign the electrical system if you plan on a longer run time. Whereas the kit battery is capable of several hundred amps in short bursts, a car battery is capable of 1000's under the same condition. The choice of that battery will change a lot of design criteria.