Here's what the winners are going to do. Their dads are going to go to a site like
THIS and buy what they need to make a winning car.
I can recommend
THIS car chassis from experience. It's a simple enough cut that it doesn't scream "store bought". Have you kid slop some paint on there and it'll pass for home made.
Go with the lightest, thinnest wheels you can find. But be sure they started out as stock BSA pine derby wheels. We used
THESE. Unless someone picks up the car and inspects the inside of the wheels, they look identical to the regular, stock BSA wheels. And modifying them by thinning the walls and such is perfectly legal. Just that most people don't have the equipment to do it really right. But what you want is that 1-gram wheel. Nothing more. NOte: these wheels are fragile. Have back-ups in case someone man-handles the rig before race time. Same with the axles.
Use
these axles. Very light, hardly any friction, very fast.
You want as much of your weight on the BACK as possible. That's why the holes are drilled in the back on the chassis. And you want your car to weigh EXACTLY 5.0 ounces at weigh-in. Use
tungsten weightsto get as much weight on the back as possible.
Bullet Lubeis the dry lube you want after going to all this trouble to make a kick-### car.
Finally... to bring that car up to 5.0 ounces exactly, you will need a
scale similar to this one. Accurate to 0.1 grams. At the race, the officials will have such a scale.. maybe not this very same one, but perhaps something very similar. I found my scale agreed with the race officials' scale exactly.
If you follow all this, you will put together a highly competitive, and most probably winning, race car. If you try to do it on your own, you can explain to your son that this is most likely what the winning cars did, but you thought it would be a more fulfilling experience to do it all on your own.
At least this is what me and my kid did before he got kicked out. And, yeah, he won first place, and we both had a blast.