Racing a toy car on a flat surface relies on too many variables: maybe racer A pushed harder than racer B; or the floor is uneven near Racer C's car; or even that racer D just built a faster car than his opponents. To make the race more fair, start with a simpler setup, such as a long ramp that leads to the finish line.
Measure the wheelbase of your cars and add about 1 1/2 inches to that number. Multiply that number by the number of lanes you intend to make---many car ramps have four---and add 1 inch. This number is the width of your multilane track.
Measure along the width of the plywood using the number you calculated above, so you're marking out an 8-foot-long section of ramp. Cut out this section of track.
Cut out 8-foot by 1-inch track dividers from the plywood. Cut out one for each of the lanes, and one extra, making sure that each of these is smooth and straight all the way down.
Glue two track dividers into place along the outer edges of the track and then screw them into place.
Measure the width of the lane from the right-hand track divider---that's the width of your car's wheelbase plus 1/2 inch---then glue the next track divider in place. Make certain that these tracks are the same width the entire distance down the track, and then screw the divider into place at 2-inch intervals. Repeat with your remaining dividers.
Cut the remaining piece of plywood into two 5-inch-wide pieces, which act as the side wall of the ramp. These pieces will prevent the cars from flying too far if they should leave the track.
Glue and screw the side walls onto the sides of the track so they are perpendicular to the edge of the ramp, sticking up above the track dividers.
Measure the length of your car and add about 3 inches to that. Mark this on the underside of your ramp, in from the top.
Cut the 1-by-2-inch plank into two 3-foot sections and two 1 1/5-foot sections. These will become the feet. Also cut two sections the same width as the track, which will become track supports.
Glue and screw the track supports to the bottom of the track. Attach one below the point marked in Step 8 and one about halfway down the track.
Glue and screw the longer legs to the top track support so they lift the ramp off the ground. Make sure the two legs support the track evenly.
Repeat with the shorter legs and the middle track support.
Allow the track to dry overnight. In the morning, sand the track until smooth.
Drill a 1-inch hole In the center of each of the tracks, just below the upper track support. Make sure the four holes line up with each other.
Measure about 4 inches below the first hole, and drill another in the exact center of the track.
Cut out smooth slots by joining the holes drilled in each track. Make sure each is a near-oval. Sand these holes smooth.
Cut the dowels into 4-inch lengths. Use one dowel for the starting pole in each of the lanes and the extra one for the handle.
Cut the 1-by-1-inch wood to the width of the tracks. This will become the starting axle.
Hold the starting axle beneath the holes you cut in Step 1 and mark the exact centers of these holes.
Drill about 1 inch into the center at the top and bottom of the starting axle. Also cut about 1/2 inch into the axle at the marks made in Step 6. Turn the axle over and make another 1/2-hole between where any two of the holes on the other side are.
Glue the starting poles and handle into place on the axle.
Place the axle between the two upper legs so the starting poles slip through the slots. Place two washers on each side of the axle and drill through the legs with the 2-inch wood screws so the screws fall into the top and bottom holes. You should be able to pull the handle and watch the starting poles drop below the track.