when i was in cub scouts i pulled first place every year in my pack... it was awesome...
we special ordered some 1/4 inch tungsten rods and used them as weights so we could make the cars a lot thinner
also put the weight as far back as you can so it has more time falling down the slope therefor more momentum to maintain speed on the flat
and drill your own axle holes, sometimes the stock ones are crooked and if you make the wheelbase longer there is less wobble in the car....
if you have a drill press you can polish the ridges on the outside of the nail...
do some of that and y'all can pull first every time!