I think he was asking about a GT? If it is supercharged, it is much safer to run 93 than it is to run 87 or 89. In a GT, (Naturally Aspirated, except for the non-fleet 2006 - 2007 GT's that came supercharged), I'd just run the 87 or 89 since the higher octane won't matter as much in a N/A engine