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Maybe they run a CAI and aftermarket exhaust? My mustang gets alot better mpg since I did that.2010 6.2L using shell 91. Like many here would agree, keeping it under 70, 65ish you can see some decent numbers. Anything above that really is hard to get good figures. I have no idea how some guys are saying they are getting 15mpg doing 70, 75 mph (maybe good tailwind?)
With 87 oct I had an avg of around 12mpg, switching to 91 I get 15 city and upwards of 17.3 at times on highway.
use e-30 ethanol it's better than 91 imo cheaper too