The Southeast Division recommended groupings are five groups. One is ITB and ITC with Production cars, GTL, SPU and SRF, with SM and SSB/C in another group. This is the way I usually see it done, with SRF sometimes split into their own group. If time is available, or the the field is large, there may be as many as 7 or 8 groups. The race organizers can split it however they want in order to balance the group sizes, although they usually try to avoid combining groups to avoid permanent number conflicts.