I'm guessing you have a SRT6, personally I wouldn't run 89 in mine, but... for the record, 89 octane recently tested, (by the state), at stations around my area proved that the 89 octane was in most cases over 90. Most "super" designations start at 91, so if perhaps if you have a SRT and don't run it in a manner likely to initiate detonation it may be perfectly fine...But I'm not a Chrysler/Mercedes tech nor pay for your car, just some guy with an opinion...and you'll probably get lots of opinions from people just like me... Bottom line if you don't run the car hard with the 89, my guess is 99.9% fine, my hold back is not running it hard without ensuring high octane. For your question about damage. The main concern is detonation, and the damage that comes along with that, (piston fractures/burns, valve damage, rod and bearing damage)