A major factor for the travel time of the car is the angular momentum. If the car doesn't go straight, the wheels will ride up on the median strip, converting forward speed to chattering increased height. You can hear the losing cars chattering their way down the track. The car manufacturer incorrectly recommends that the extra weight be placed in the center of the car. This is like putting a mid-engine roadster in a drag race.
Drag racers are long.
They try to maximize their angular momentum. Mid-engine sports cars try to minimize the effort required to turn. I placed the fish weights evenly in two pairs of holes drilled in the front and back of the car. This created a barbell effect, maximizing the angular momentum. My car wanted to go straight.