Cadillac Repair: GAS (PREMIUM UNLEADED), cadillac eldorado, ht series

Question
Dear Ben,

I just want to verify something regarding the note or sign printed to the dash board on my 1992 Cadillac ElDorado, 4.9L engine.
It say's that PREMIUM UNLEADED GAS ONLY TO BE USED ON THIS CAR.
Mr. Trigoboff, is this a very critical and important thing to be followed?,
WHAT WILL HAPPEN TO THIS CAR IF ONLY REGULAR UNLEADED GAS WAS BEING USED??? WILL THIS RUIN THE CAR PERFORMANCE OR DAMAGE ANYTHING IN THE ENGINE???

PLEASE EDUCATE ME ON THIS MATTER.

Thank you very much.
Rey M.  

Answer
DO NOT run the HT series cadillac motor on anything less than 91. But as a test, use up all your gas and put 2 or 3 gallons of 87 in, you wont permanently damage your engine but it will knock like crazy, and then just fill the rest of the tank with 93 and youll be alright. Basically it will just knock like crazy and you will get the engine extremely dirty inside.