The idea behind a spec/stock Slash is to limit the amount of hop-ups or modifications to the RC to control costs. I'm sure a lot of clubs have different rules. Most spec Slash classes only allow the Titan 12T brushed motor to be used. Some clubs may allow certain aftermarket parts like RPM bumper, and hubs. Some clubs may allow the Traxxas LCG chassis. Like tntpoof mentioned, get with your local club, and find out exactly they allow.