Friedrich Ostertag wrote:

It IS neccessary. Just to name an example, evaporation proporties need
to be adjusted to climatic conditions. Try and fill your car in AZ,
preferably at a high altitude location, then drive it to one of the
northern states without refueling (probably won't work with the mileage
you get on current US cars..:-)) and try to start it in the morning at
below freezing temperatures. You will be surprised.

By that logic then, we'd need to have a different blend of AVGAS for
each density altitude that we fly at, which is, of course preposterous.
Now I am not arguing *for* the archaic engine designs now currently in
use by we average GA airplane owner. Perhaps if FAA certification was
not so costly, ponderous then engines of more modern design could be
be made affordable enough for the average guy to install in his plane.
(yes I know some of these engines already exist but will they ever
be STC'd for the current fleet????)

Motor vehicle engines are not weight limited and are generally far more
advanced in design than the average piston aircraft engine. This technology
gives them the capability to adjust their fuel air mixtures and ignition
timing based upon real time conditions so they can always operate at maximum
efficiency at any altitude or temperature (after being warmed up of course).
Different fuel blends are not necessary unless you carry emission standards to
exaggerated extremes, which is exactly what is going on in this
country today.