Gasoline grades also vary among brands and with elevation.

In my '91 Westy, standard trans, I averaged 20-22 mpg on 87 octane. While
out west this summer in dry, higher elevation areas, I found that 'regular
unleaded' was only 85 octane. Being VERY CAREFUL not to purchase any gas
that was "blended", as many of the midrange octanes were, I found that I 
actually got 22-25 mpg on the 85 octane! And the engine purred. On the way
back east, you could see the octane of the "regular unleaded" go up as you 
lost elevation.

I ran "regular unleaded" no matter what the octane on the entire 8500 mi trip
with absolutely no problem. I plan to do the same in my "new" '91 Westy when
I get her.

Kenyon
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  Kenyon Fairey, Re.D.                            Adjunct Assistant Professor
  Head, Help Desk Services &          Human Dimensions of Resource Management
        Software Support                             Department of Forestry &
  Office of Information Technologies                      Wildlife Management
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  A 117, Lederle Graduate Research Center   Internet -- KFairey@OIT.UMass.EDU 
  University of Massachusetts                  Phone -- (413)-545-4366    
  Amherst, MA 01003                            FAX   -- (413)-545-3203