Are you building the car for a specific championship? If so you can get the regs on what is and isn't allowed from there. If you haven't got a specific championship in mind and are planning to pick and choose events then the class structure may be different form event to event, normally on single venue events it's broken down by engine size - mods beyond that are free within the confines of the blue book rules. If you can give us a bit more info on what you're going to use the car for we may be able to provide some info
