If there has been a thread about this before - sorry - please reply with the link

if not --

those of you that have stock 2.4 liter engines: do you use "regular", "mid grade" or "premium"?

here in Colorado the posted octane numbers are 85, 87 and 91 respectively

I have always believed that if you can't hear pinging, you are OK

I ran 85 in my 73S for years and then a mechanic I trust said i should run 91

isn't it true that higher octane fuel is more difficult to "combust"?

could 91 cause a misfire in my car?

and the subject of ethanol: the nearest place to get 87 ethanol free is 23 miles from my house - do you folks seek it out or not worry about it?