Claim: GT cars are divided into 2 or 3 subgroups (GT3, GT4, and GT Open), on the other hand, TC, which are heavily modified road-going cars used in motorsport road racing competitions, are divided by calculated engine capacity (TC1 - TC4).
Evidence: Group GT3, known technically as Cup Grand Touring Cars and commonly referred to as simply GT3, is a set of regulations maintained by the Fédération Internationale de l'Automobile (FIA) for grand tourer racing cars designed for use in various auto racing series throughout the world. The GT4 European Series is a sports car championship created and organised by the Stéphane Ratel Organisation (SRO). The International GT Open is a grand tourer-style sports car racing series founded in 2006 by the Spanish GT Sport Organización.