Im wondering if it would be possible (or plausible) to run half 91 octane gasoline and half E85. This would make the octane effectively 98.5. My friend has an 05 V6 mustang, with a tune that requires 91 octane. He says he put half 91 and half E85 in, and its running fine, better than fine actually. He says he seems to have more power, and its running slighly better.