I regularly monitor how much fuel I use by entering the details on a spreadsheet. My sportster was doing around 38 miles per gallon, but since I had the new exhaust pipes fitted, I'm now getting over 50mpg. I'm not really up on fuel quality details, but I accidentally filled up with 97 Octane instead of the usual 95 Octane. Does this make any difference with Harleys? Or could it be that the new pipes are closer to the air intake and the engine warms up faster?