Just gonna throw this out there, but the octane rating has to do with the pre-combustion resistance of the gasoline (also know as "knock" or detonation)... the higher the octane the more resistant it is to pre combustion (has to do with the speed at which the gas burns). Pre combustion tends to happen at high RPMS or when pushing the engine hard in high compression conditions or engines. So if you're turboed or have a car with a specific "high performance" engine (protege engine is not high performnace) you need to use higher octane gas or you computer will reduce the timing in order to keep pre-combustion from happening thereby reducing your horsepower. But in our engines which are timed to burn 87 at a certain rate, if you put in a higher octane it shouldn't effect gas milegae at all, either way and there are no real benefits, other than the gasoline manufacturers making more money off of you. When you use a fuel with a higher octane rating than your vehicle requires, you can send this unburned fuel into the emissions system. It can also collect in the catalytic converter. When you over stress any system, it can malfunction or not do what it was designed to do properly. Sometimes an early warning symptom is a rotten egg smell from the tailpipe. Easy fix, go back to using regular 87 octane gasoline. The rude odor usually disappears after several tanks of gasoline.
FYI - For those with turbos or who really want to use higher octante gas there are a bunch of Mohawk and Husky stations in the Vancouver area that sell mid-grade for the price of regular... they don't actually even have regular. There is one just down the street from my place in North Van on third street.
