[azasadny]

Mike,

My son and I built one of these a few years ago, we drilled out the middle of the car then took apart some shotgun shells and loaded the hole with lead shot. We weighed the car carefully and left it an ounce or two below the allowed weight. We also polished the "axles" (nails) with steel wool, then put powdered graphite on them. The car ran really fast but was just barely beaten by two other cars. Have fun!!!