Sounds like your motor is gone. You said you put 91 in it, was it a engine knock, or detonation? You way you described its not detonation, but you motor knocking. Did you check your oil?
I've read in here that the 86 SVO intake and Turbo coupe intakes are better than the 84 SVO intake. Is this the same intake as the NA cars have from 87 up, or is it just the turbo cars?
TIA