You are probably looking at the RON (91), not the (RON+MON)/2 which is 87. Check your owner's manual. What you see at your local gas pump is the (RON+MON)/2. It is very unusual for ute quad to require 91 gas pump octane rating, especially considering 360's relatively low comp ratio of 8.3:1. As a rule of thumb, you want to use the lowest octane rating possible without any detonation going on inside the combustion chamber. Here is why:
>Lower the octane, more flammable meaning more potential (chemical) energy stored in it. >Higher the octane, more additives are added to resist the combustion.