Hello everyone, i have a question...i currently have about 1/3 of a tank left in my GT with 87 ocatne, i wanted to go fill her up with 91, since i will be getting my tune soon with 91 octane. Will having 1/3 of the 87 mixing with the 91 do any harm? Dumb question i no, but ive never filled up any other octane that 87...so i really dont no hahaha thanx everyone!:kooky: