http://www.e90post.com/forums/showthread.php?t=716743
Start here,
Essentially you need a proper tune to run a higher ethanol blends. On some aggressive MAPs, you can mix a bit of E85 pump (3 gallons) with 91 octane to run, if 93 isn't available. But realistically you need a proper tune.
Read the tunes, they have specific mods required when blending higher ethanol percentages.