Mileage Per Gallon

I know for sure we got some crappy lower octane than advertised (87) gas in the NC mountains, and when we had a really long hard pull on the interstate coming back, we got some wicked bad pinging for the two seconds it took me to shut the cruise control down when big Ex shifted to 3rd at 65mph. Next fill up we put in a higher octane (91), then got into the mountains again.. no pinging at what appeared to be the exact same conditions. (RPM incline, and road speed)

I don't think I have ever heard of damage from a higher octane being used, it just isn't always helpful or needed. Most modern vehicles will adjust ignition timing and spark to compensate anyways. Our GTi does that. It wants 93, but you can run it on 87.. and you can tell when you do. My guess is it cuts boost and timing advance pretty harshly, because merging and passing are noticeably different.