Let me start off by saying I have been using 93 octain gas for almost 2 years up until about 3 weeks ago I tried 87 to see how it ran. I am now getting about 1 degree more knock retard at WOT. I have a tune for premium fuel from Ion so I know I need to lower the timing a little. But the odd thing is for the last 2 years of running 93 I got 13 to 14 MPG on a mixed highway and city driving. When I switched to 87 the first tank I got 17.4 MPG. I thought it was just a fluke but I have now been through 3 tanks of 87 and it's 17 MPG every time. I am not sure how or why this happened, could it be somthing with the tune? Let me know what you guy's think.