I finally got through the last tank of 87 and put 91 in and loaded the 91 perf tune. Wow, what a difference. The Xcal rocks! The Expy seems so much faster now. I really haven't pushed it to hard yet, but I can for sure say this is definately worth the $$$. Do yourself a favor and get one of these if you can. Any other perf mods will fall short of this for the money.