I have a 2002 SS. It says in the manual to use 90 octane but that you can use anything 87 or better. When the gas went up I tried the 87 and found that I got about 2/3 of the mileage with it. The engine de-tunes itself and becomes less efficient. I do not know what part of the country you are from, but in the Boston area the differences in price between 87/89/93 is abou $.10 per gallon with each upgrade so if you are buying a high performance V-8 put in the high test.