So I just ordered my Diablo Intune and should be here in a few days. The premium fuel in my area is 92 octane, so I was wondering which would be the better tune for me to run the 91 or 93? Thanks in advance!
Due to refinery gasoline blending practices, many times the 92 Octane gasoline will actually turn out to be closer to 93. We call it give away, it is often an insurance policy against the alternative. Being below 92 - we call that breaking the law.
The E10 requirements seem to have increased the give away from many refineries since Ethanol is an octane booster that is often added later, not during the actual primary blend process, so is harder to accurately account for.
So you could conceivably run a 93 tune on so called 92 gasoline with no problems, but you could never guarantee the octane in the gasoline was 93, many times it will be though. It depends upon the refinery it came from (some are able to blend closer to the specs than others).
The other thing to consider is that even if the gasoline left the refinery closer to 93, if it sits in the tanks for a while (as premium gas can do at some gas stations) it may start to degrade it's octane number. Butane for example gives a good octane boost, but it is also one of the first products to evaporate off and bleed out through any pressure relieving system in the storage tanks.
So no clear answer from me, but just something to consider.