We talked in great detail about this in mechanical engineering school, especially in my class internal combustion engines. The ultimate answer is that everyone's replies are correct. You should not run 89 octane fuel. All fuels have what we call an adiabatic flame temperature. This is a temperature at which fuels spontaneously begin to burn. Putting 89 octane fuel in your high compression engine can cause the fuel to ignite too early and essentially change the timing of your engine. This, as others have mentioned, can do big damage. I hope this helps.