▁One ▁rules . ▁The ▁ 1 9 5 0 ▁event ▁was ▁again ▁held ▁in ▁August , ▁but ▁from ▁ 1 9 5 1 ▁on wards ▁– ▁apart ▁from ▁ 1 9 5 7 ▁– ▁the ▁International ▁Tro phy ▁was ▁cont ested ▁in ▁April ▁or ▁May , ▁near ▁the ▁beginning ▁of ▁the ▁World ▁Championship ▁season . ▁The ▁timing ▁of ▁the ▁event ▁often ▁attract ed ▁many ▁top ▁teams ▁and ▁drivers , ▁allowing ▁them ▁to ▁pract ise ▁in ▁racing ▁conditions ▁before ▁the ▁season ▁became ▁too ▁serious . ▁From ▁ 1 9 5 2 ▁the ▁tro phy ▁was ▁also ▁sp or ad ically ▁opened ▁to ▁drivers ▁in ▁the ▁Formula ▁Two ▁category , ▁as ▁well ▁as ▁being ▁run ▁to ▁F 2 ▁reg ulations ▁in ▁those ▁years ▁that ▁the ▁World ▁Championship ▁was ▁also . ▁ 1 9 7 8 ▁saw ▁the ▁ 3 0 th ▁running ▁of ▁the ▁International ▁Tro phy , ▁and ▁the ▁last ▁under ▁these ▁rules ; ▁with ▁the ▁increasing ▁complexity ▁of ▁F 1 ▁cars ▁it ▁simply ▁became ▁too ▁expensive ▁for ▁teams ▁to ▁contest ▁non - ch ampion ship ▁events . ▁ ▁From ▁ 1 9 7 9 , ▁the ▁tro phy ▁continued ▁as ▁a ▁Formula ▁Two - only ▁event . ▁When ▁F 2 ▁was ▁replaced ▁at ▁the ▁end ▁of ▁ 1 9 8 4 , ▁the ▁tro phy ▁switched ▁to ▁the ▁new ▁Formula ▁ 3 0 0 0 ▁rules ▁from ▁ 1 9 8 5 . ▁In ▁turn , ▁it ▁was ▁replacement ▁of ▁F 3 0 0 0 ▁by ▁GP 2 ▁in ▁ 2 0 0