Mega Gs use neo traction magnets and the pockets for those are quite small. Lead or tungsten would be a better choice than brass for the weight material. My club mostly races pancake cars, chalk that up to failing eyesight and slowing reflexes! We have a couple of classes for inline magnet cars, but we have not run tham for several years. We did do a race for G-jets this year, they are about halfway in speed between a really good SS T-Jet car and a regular inline magnet car. G-jets have a detuned armature and are run at 12 volts, but they are nearly as fast in a straight line as inline magnet cars.