0 0 ▁automatic - equ ipped ▁L 7 5 ▁cars , ▁which ▁produced ▁ 2 5 0 ▁net ▁horse power . ▁ ▁The ▁ 1 9 7 2 ▁Hur st / Old s ▁was ▁based ▁on ▁the ▁Supreme ▁two - door ▁hard top ▁and ▁convert ible , ▁power ed ▁by ▁both ▁versions ▁of ▁the ▁ 4 5 5 ▁Ro cket ▁offered ▁on ▁the ▁ 4 - 4 - 2 , ▁along ▁with ▁a ▁Tur bo ▁ 4 0 0 ▁transmission ▁with ▁Hur st ▁D ual / G ate ▁sh if ter . ▁The ▁H / O ▁convert ible ▁also ▁served ▁as ▁the ▁Indian apolis ▁ 5 0 0 ▁P ace ▁Car ▁in ▁ 1 9 7 2 . ▁▁ 1 9 7 2 ▁was ▁also ▁the ▁final ▁year ▁for ▁Old s ▁to ▁offer ▁the ▁C ut lass ▁Supreme ▁convert ible , ▁until ▁ 1 9 9 0 . ▁ ▁In ▁its ▁final ▁year , ▁it ▁was ▁the ▁best - s elling ▁convert ible ▁in ▁the ▁U . S ., ▁with ▁ 1 1 , 5 7 1 ▁sold , ▁or ▁ 1 6 % ▁of ▁the ▁market , ▁be ating ▁the ▁E ld or ado ▁and ▁Cor v ette . ▁From ▁ 1 9 7 3 ▁to ▁ 1 9 7 5 , ▁the ▁only ▁Old sm obile ▁convert ible ▁offered ▁was ▁the ▁full - s ized ▁D elta ▁ 8 8 ▁Roy ale . ▁ ▁Third ▁generation ▁( 1 9 7 3 – 1 9 7 7 ) ▁ ▁In ▁ 1