Dealer said it didn't matter either way. You are going to get all 303 hp. However, this is the old Vette motor, so I would guess it would be wisest to use atleast a 90+ octane. I have always used 91 in it, with the exception of one tank that the wife filled up w/ 87. Honestly, I couldn't tell the difference.
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2007 Shadow Gray Metalic GXP
K&N Air Filter & More goodies to come.