In the 240SX the driver weighs 170 and we have about 50 or so lbs of ballast, in the RX-7 I cannot remember how much we added but it was more than 20, if I remember it was somewhere around 50lbs.
Jude has a real knack for building light cars and prides himself on it. Our AS Camaro that we built last year was siginificantly under weight.