Octane is the rating in which fuel ignites under pressure. The only reason to use high octane fuel is if you have a high-compression (racing) engine that when low octane fuel is used you have pre-ignition or pinging. When an engines pings not only is it not performing well but it can damage the valves.

If you don't have a high compression engine you are throwing your money away paying for high-octane fuel. The best bet is to go with what your owners manual calls for. I have a 135 hp Optimax and it calls for 87 octane just like my Chevy Silverado.

kc