Our Cubmaster made a car with a wireless spy camera on it. We would send it down the track just after the racing cars started and show the in car camera on a projector. One car was so slow, it got rear ended by the camera car.
We had one of our Indian Guides show up with a car that was wayyyyy overweight. The kid and his Dad got out a cordless drill and started drilling holes in the car. When it got legal it looked like swiss cheese as it was painted white. It actually did quite well.
We had one Dad show up with his son’s car in a padded case. That car won hands down, and we knew there was no way the son had anything to do with the construction. The next year we instituted a rule that the kid had to carry the car back to the start of the track for the second heat (we ran 2 heats because we could only handle 2 cars at a time like a drag strip). That year the same car in the padded box showed up. When the son was carrying it back to the start, he dropped it and it broke into many pieces. The Dad spilled his drink.