LuckyGuy

Would you run 91 octane that is ethanol-free or 94 octane that contains 10% ethanol in a Z06 that has not been modified or tuned?

Which fuel is better for the engine?

badhabit_wb

I run 93 octane ethanol free. If I couldn't get higher than 91 ethanol free I would use the 94 with ethanol. I just did the 100 octane calibration on mine so that I could use 100 octane at the track and see an improvement.

davepl

I'd take the 94 myself. If I could get 92-93 without ethanol, that'd be even better. But if it's below 92, I'd go to the Ethanol blend to get the extra octane.

Bill Dearborn

I was at a track event where the outside gas station only had two fuels. 90 Octane ethanol free and Diesel. I went through 3 tanks of that gas with no issues. Car ran fine at wide open throttle for extended periods. The nearest station with 93 with Ethanol was over 5 miles away and we didn't have time between sessions to get there. Car didn't have any changes to the tune either aftermarket or GM provided.

Bill