The tune it is on 87 octane. I will try 91 this Friday.I set my tire size to 36.5" and wow this thing gets up!! I am getting 17.5 mpg on hwy and before i was lucky to get 15 mpg. The take off from a stop is crazy. Punching it from 70 mph to 100mph it puts you back in the seat lol. This is so worth the money.