sorry if this is long.........ok, fuel octane numbers are the most misunderstood reason people use higher octane fuel.first off, the higher the number the SLOWER the burn of the flame front. 89 octane burns hotter than 91 octane in the same engine. thus the misconception if you use higher octane you get more power. not true. higher octane was developed for higher compression engines to control engine predetination, not to produce more power. thus using 89 will produce more power verse 91 in a lower compression engine. the reason Mercedes recommends 91 octane in some cars is because high compression and more ignition timing to produce the horse power they designed to to make. the higher the compression the more dense the fuel charge thus more power, but this also leads to predetination due to the the fuel charge squish wanting to burn sooner during the power cycle. compression ratio, timing and cam shaft all play into the factor of what fuel to burn in each engine. we found running 91 octane in the race engines made more power than 108 race fuel but created more engine temps during the long hard pulls. just a few thought before putting high test in the tank for no reason. if you want to go deeper into this pm me for more discussion. take this post as you will but i have burned up a few engines running the incorrect fuel in the application that required a cooler burn than what we built

Joe