The operative phrase there was "stock engined". With stock settings and 92 octane, my car gets about 3 mpg less than with the Superchips set to 91 Octane. This is on the run to my dealer (about 25 miles one way) so the conditions are as close to identical as possible. I haven't tried stock with 87 or 89 so I can't give any feedback on that. I usually fill the car around the half tank mark so with the other advantages of the higher state of tune, I figure the extra $2 per fill ($4 per tank) to be worth it.

Redbeard

 

I have an 2007 R/T. Owners manual states best performace with 89 octane. What do they mean by best performace. My wife has an 2005 Chrysler Pacifica and that says the same thing. We have been using 89 octane only....I dont want to shorten the life of our babies