1. Have your son draw a design on paper then cut it out and use it as a template. I use the paper with the little squares on it to make it easier for him. Draw a side and top view on the paper by tracing around the block of wood.
2. Keep the car a full seven inches. It has to do with the physics of velocity and length of travel of the weights.
3. Use the full 2 3/4 inches (outside wheel to outside wheel) that the rules give you. This will allow the wheels to travel farther before hitting the center strip.
4. Leave a lot of wood in the back to put in the weights. You want the car to weigh as much as possible, not exceeding 5.0 ounces.
5. Use the groove closest to the end of the block of wood as the rear axle.
Note: The Race Starter will place the car on the track according to axle location. The back axel is nearest to the end of the car. The front axel is furthest away from the end of the car. This determines the direction the car will race unless the contestant clearly marks "Front" on the car.
6. Do not make the front of the car pointed. It is hard to set up against the starting dowels.
Inspect your axles, right where the wheels rest on them. There are typically manufacturing stamp marks or even burrs right where they touch. They should be as smooth as possible using a small file or fine grit paper.
When you insert your axles, be sure there's sufficient room and play between the head and the wheel when the wheel is resting against the block. There should be plenty of room to apply dry lubricant to the well under the nail head and into the hole in the wheel. Spin the wheel to bed as much lubricant into the surfaces as possible, so all wheels spin freely and true.
More than anything else, you want your car running straight down the track. Bouncing back and forth against the track guide will slow you down. Carefully insert your axles into the pre-cut channels in your body block. TEST your car running it down a sheet of plywood or other flat smooth surface. It should run straight and smooth. If not, it needs an alignment, just like a real car. There are methods and tools available
9. Use your imagination. Be creative. Shape has the least to do with winning. A beaver driving a log or even a pickup truck is more interesting than a wedge and will be just as fast. The aerodynamics of a small block of wood doesn't mean much in thirty feet.