I just stumbled across this thread....I run 93 octane, I paid $2.68 the other day. Like what has been mentioned a few times, with 11:1 compression, detonation is an engine killer, so you need a slower burning fuel (higher octane). The goal to reach maximum efficiency in an internal combustion is to have a "flame front" that burns at around 100fps...Think of it as a controlled burn, rather than an explosion.