▁Times ▁Grand ▁Prix ▁and ▁the ▁Road ▁America ▁ 5 0 0 ▁were ▁also ▁r ounds ▁of ▁the ▁ 1 9 8 1 ▁I MS A ▁GT ▁Championship . ▁ ▁The ▁ 6 ▁H ours ▁of ▁Day ton a ▁was ▁restricted ▁to ▁Racing ▁Stock ▁class ▁cars ▁ ▁( i . e . ▁I MS A ▁R S ). ▁ ▁The ▁ 2 4 ▁H ours ▁of ▁Sp a ▁was ▁restricted ▁to ▁Belg ian ▁Tour ing ▁C ars ▁ ▁( i . e . ▁Group ▁ 1 ). ▁ ▁World ▁End urance ▁Championship ▁of ▁D ri vers ▁The ▁World ▁End urance ▁Championship ▁of ▁D ri vers ▁was ▁open ▁to ▁FI A ▁Group ▁ 1 , ▁Group ▁ 2 , ▁Group ▁ 3 , ▁Group ▁ 4 , ▁Group ▁ 5 , ▁Group ▁ 6 , ▁Group ▁C ▁and ▁G TP ▁cars ▁and ▁to ▁I MS A ▁GT X , ▁I MS A ▁G TP , ▁I MS A ▁A AG T , ▁I MS A ▁G TO , ▁I MS A ▁GT U ▁and ▁I MS A ▁R S ▁cars . ▁ ▁D ri vers ▁Championship ▁points ▁were ▁awarded ▁on ▁a ▁ 2 0 - 1 9 - 1 8 - 1 7 - 1 6 - 1 5 - 1 4 - 1 3 - 1 2 - 1 1 - 1 0 - 9 - 8 - 7 - 6 - 5 - 4 - 3 - 2 - 1 ▁basis ▁to ▁the ▁first ▁twenty ▁overall ▁finish ers ▁at ▁each ▁round . ▁Bon