[dreksnot]

Depends on how it was tuned... ask you tuner.

By the fact that it's more alcohol, then you'd be using more fuel. "They" say you usually use 30% more volume of fuel E85 over 93/91.

Possibility: the tune was correctly setup in all the alcohol tables to will add slightly more timing in the higher RPM/load areas. You will also need slightly more fueling but it looks like your fuel system should be able to handle that. I've been told by several tuners that anything over 40% alcohol starts to run about the same, and I interpreted that as hitting diminishing returns. I haven't experimented enough to know any different yet.

If the tune was set up correctly, then you'd notice a difference driving the car with straight 93/91 octane compared to having a tank with +50% alcohol in it, by the additional timing on a WOT pull; but likely not noticeable between 50% and 75% alcohol difference.

I've attached a couple the alcohol tables that adjust timing for alcohol. The smaller table is the percent of timing on the larger table that is added/subtracted to the main timing table. These are my chosen numbers as my local station runs 70% max. Sometimes I fill up in a town on the way to the strip and it has been 85% at time. I run with whatever I have in the tank as I am tuned for the whole spectrum of alcohol in the fuel.

Also, you have an octane and a alcohol power enrichment tables. The more alcohol, the more swayed the PE will toward that ratio (if the tuner used different PE ratios).