Advanz made a post that I had wasted my money by going with Renntech, that the SI kit was a fraction of the cost. So I replied to ask just exactly what the fraction was, but I did not get a reply, so I really don't know how much money I wasted, HA. As for the 91 or 93 question, in my opinion a company that is claiming the higher H. P. gains are probably going with 93 so they can crank up the timing a little more. From the info I've received about the remapping process it's not all about timing curves and octane, it also has a lot to do with air/fuel mixture verses RPM's and a whole lot of other crap that I know very little about, so I better just stop with the info stuff before I stick my foot in my mouth.