Octane on 17' GT

[Bluemustang]

I have definitely felt a different when going from 87 to 93. I noticed immediately in the midrange power. The car seemed happier to rev and smoother overall. Since the first fill up with 93 octane I stuck with it.

Now running E85 and a much bigger difference there. The lowest octane I've run in this thing in a long time was 92 octane, only because 93 or E85 wasn't available.

I even notice the difference between gas stations and now I only use Sunoco or Shell unless I have no choice. I waste a bit of money on E85 and 93 but I choose to put the highest octane in my car for peace of mind. YMMV

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[Taneras]

The thread posted was for a S197 coyote. These engine have different heads, different cams, different tunes.

And simply changing fuel and throwing it on the dyno isn't suffient. From my understanding, you typically need to run the car through nearly a full tank of fuel for the timing to fully adjust to the new fuel types.

True, but at least its something to support the claim that there is a significant difference between 87 and 91/93 as opposed to the counter claim which so far I haven't seen any testing for. Also, Ford has made the same distinction for peak power numbers for the S197 as it has for the S550, those horsepower figures are on 93 octane. Clearly there's a difference in both cases and there's evidence in the S197 that its a significant difference. Believe what you want, but it seems more likely to me that there is a similar significant difference in the S550.

And its my understanding, from talking to Lund about my flexfuel tune, that after 3-5 minutes my S550 will be able to adjust to a new fuel type and I will be able to do WOT pulls. If that's true, it would seem someone would have to try and not allow the computer the ability to adjust to the new fuel type as the window is so small where its adjusting.