I have hemifever 89,91,and 93 93 is awesome but I only have two gas stations over here that has 94 octane, and both contain ethanol in their gas.. Shell has no Ethanol but I can only have 91 octane. I prefer Shell since it has the best additive to the gas and contains no ethanol.. Thing is I see no difference between 89 and 91 Hemifever tune. I puch it to the floor and it doesn't open up like the 93 Tune. Either way it's still way way much better then stock and it's worth the money just to drive it with the hemifever tune. It's a new jeep. Diablo better get their shit together with the ABS this is going on for way to long. Safety should be taken in priority.