No matter what tools we use, or which materials, or what color we paint our sweet mods, performance all boils down to physics. Science always wins!
Now, while Hot Wheels are quite smaller than your classic Pinewood Derby cars, it's all gravity racing and the same theories apply. I was killing some time at work and found some knowledge. Some of this gets pretty deep in the weeds but it's all fascinating and a great bit of learning. Even if you don't understand all of it (I don't), there will be some tidbits you can pull out.
This video does a good job explaining the science in terms of how you want your cars to handle energy. Some of it may be hard to apply outside of Pinewood Derby but it is very enlightening.
The PhD mentioned in the video has an exhaustive list of research about Pinewood Derby physics. It's all very math-y and so a lot of it was way above my head, but it made me feel smart and had me thinking more about what I can do to make faster cars.
For all the TL;DR crowd...put your weight near the rear of your car and focus on your whees/axles. Friction is the enemy of all racing.