Is this for a school or some kind of competition? Either way, if you want to go fast and above all, WIN, the most important thing for the car is to get it as light as possible. This means getting the total weight down to the bare limit of weight, so if the minimum is like 45 grams, try to have it be 45 grams on the nose. With these types of cars, and the drags they do on the fishing line drag tracks, the race is going to be done too soon for aerodynamics to be a major factor, but consider them anyways, both for looks, plus it does help a little bit. You don't want to go to thin in the car, or you will start to have to worry about it snapping. My advice to you is to put the wood you are going to be using in the oven on a low heat and keep an eye on it, checking it every half hour or so. The heat will draw the moisture out of the wood, keeping the solidness of the wood there, but taking the water weight with it, thus making it lighter. By doing this, you will not have to take as much wood off of the car. I would also suggest getting some steel wool, polishing compound, an old rag, and a drill and polishing up the axles of your car. You want the wheels to spin as freely as possible, almost like there's a set of ball bearings in those suckers. After you get the axles polished up real nice, use some dry powder lubricant and puff some in the hole of the wheels. This will create even less friction and resistance and allow the wheels to spin that much faster. When you put your wheels/axles on the car, make sure that they are all square to the car and aligned with each other. You want the car to run as straight as possible. Test it out by giving it a light push and watching its path. Adjust the axles until the car rolls straight. The last thing I have to say is that if you are running them on the string track, which I assume you will be for safety and control, take car to align the eye hooks or whatever fastener they give you to attach the car to the line. Have the eyehooks be straight inline to keep the resistance on the string down and the car from going crooked.