[spool twice]

I would at least run enough to get near a 0 value in timing retard (JB4) or very little to no timing corrections (Procede and Cobb) for the map you plan to run; it will take some experimenting but rewarding because of the results. For me, that means mixing 5 gallons or E70 (31%) to a full tank of 93 octane on map 3 set at 17.5psi.

FWIW, our Brazil counterparts have the same fueling system as we do and they have mandatory E25 content.