changing fuel octane when using 5* Tunes
 

i just ordered my SCT tuner with 5 star tunning tunes and i cannot wait to receive them this friday. i have a question though. lets say i have 1/2 tank of 89 octane gas, running my 89 performance/Tow tune and its time to fill up because the nearest gas station is too far to make it, but the gas station doesnt have 89 octane gas. my only options are 87 or 91. what would be my best option to put into it and would i have to switch the tune? (i also got 87 performance/Tow and 91 race tunes) i just cant wrap my head around this since before this truck i had a 6.0 Powerstroke diesel and i only had 1 option... lol. thanks in advance.

Never use a lower octane than your tuned for, put in the 91, and no you don't have to change the tune.

changing fuel octane when using 5* Tunes
 

Gotcha thank you for that bit of info. Just outta curiosity, what would happen if I used a lower octane fuel with a higher octane tune?