I can do one better and give you a copy of the rulebook
You can ask for one anytime at Kartzone.
But in short these are the basic descriptions, although everything is more explicitly outlined in the rule book.
Street Light / Heavy - street cars meeting the minimum displacement to weight ratio, no performance engines (B series engines, K series engines, 4AGE, 3SGE, 4G63 DOHC, RB20, etc), no supercharged or turbo engines, no coilovers, no all wheel drive cars.
Super Street Light / Heavy - street cars or modified cars meeting the minimum displacement to weight ratio, forced fed engines allowed, performance engines allowed, coilovers are allowed, forced fed all wheel drive cars not allowed.
Modified Light / Heavy - street cars or modified cars meeting the minimum displacement to weight ratio (heavier weight penalty compared with the open class cars)
Open - street cars, modified cars or race cars still with minimum displacement to weight ratio
Displacement to weight ratio computed here:
Kartzone Weight Calculator
General rules:
Full exhaust pipe until end of rear bumper.
No slick tires.
Extra weight must be bolted securely.
Helmet required.
Seat belt required.
The weight to displacement is very important here since we don't want a light Honda EG hatchback running against a heavy Honda Accord, that just wouldn't be fair.