Were talking about the dart and it says 91 is ok so but thanks on the information mateNot neccessarily. The engine is built and tuned for a specific kind of gas. Using higher octane fuel that it's designed for can have an adverse affect on performance and longevity. The higher octane gas is going to run hotter which could overheat your engine and eventually burn out the engine compenents that aren't designed for it. Meanwhile you could get pre ignition with higher octane fuel than it's rated for, causing a loss of power.