I stopped using premium in the Northstar about two years ago after reading a piece on how the new cars with computerized ignition adjust to the gasoline that is used. Yes the Northstar is 11:1 compression and should use high octane to achieve maximum potential but driving around town to work it's just a waste of money. If I go out on the highway to the cottage or a long run sure I pump in the top octane. Even our 3.5 V6 Murrano has a high compression ratio and requires premium , that's how they squeeze the power out of these smaller displacement engines. Since my daughter drives it I just tell her the same thing.

The 454 is 8.5:1 compression and that hardly justifies 91 Octane in my opinion yet that's the minimum suggestion per GM so I do use it in the beast which is pretty consistent at 9 mpg around town. Shell 91 was $1.58 at my local Shell tonight, I just pumped some regular at $1.38 into the Caddy and always note the price differential. It s usually 20 cents.