I think you're a fool for betting $400 on a race with $30 cars.

Anyway, here's what you need to do.

Triple battery mod
R-Spec motor
Shave body to make it lighter
Range mods to keep it under control
Wheelie bar
Super grippy tires (more grip than anything I know of)

My recommendation for the front wheels is that you take off the tires. This way your front rims will slide and won't turn the car.

Also, I HIGHLY doubt these guys are running dual battery 3.0s and thats it, and are willing to throw $400 onto the table.