There is a line of thought that says the lower octane fuel is more volatile
and would cause more violent explosions.  Higher octane fuel is more
resistant to ignition, causing less violent explosions, but more
importantly, fewer uncontrolled explosions that would result in
pinking/pinging.  All that useless trivia aside, just about any Saab I can
think of that has been made in the past 10 years has a knock sensor that
adjusts for octane variations.  The only difference you should notice with
lower octane is reduced performance (because of retarded ignition timing to
accommodate the lower octane) and reduced fuel economy (for the same
reason).  The octane recommendation in the manual provides the spirited
performance Saab owners expect and, because the recommendation comes from
the factory, is the fuel used to calculate fuel economy during EPA tests in
the US.

The only other consideration is that high octane fuels tend to have a better
additive package to help ensure that the fuel system and fuel injectors (in
particular) remain clean.  Not all brands of fuel hold to the same standard,
but all must meet a basic minimum in all grades of gasoline/petrol that they
sell (in the US.  I can't speak to other regions).  There are many factors
that weigh in on prolonging or reducing lifetime.  Given that a knock sensor
controls the spark, in my opinion the grade of fuel used comes in rather low
in importance on the list.

Walt Kienzle
1991 9000T

Is it a turbo? In my 1997 900SE, I get the most fun with premium (92) also
the best mileage at highway speeds. If I'm just going to be driving around
town, I'll use midgrade (89). Not as much ooomph when the turbo kicks in but
acceptable. Mileage drops though.
The first time I ran 87, I thought the turbo had died. It came to life again
when I put 92 in it.

Well..... I discovered that UK and US octane are different.

Long story.

Anyway - any Saab will *like*  higher octane. The engine management computer is
designed to recognise it. Try it and see.

If I want optimum performance I fill the tank with Shell Optimax.

Graham

Here is some data that could be useful. WE bought a 2000 9-3 Viggen and
brought it from Ohio to Oregon. The previous owner apparently used regular
gas. We started filling up with premium. Data:
1st fill up - approx 27mpg
2nd fill up - approx 29mpg
3d fill up - approx 31mpg
4th fill up - approx 33mpg and stayed there (if we stayed under 80mph, of
course).

The ECU adjusts to the better gas, but it takes a couple of fill ups.

-Dima

If you have a normally aspirated engine or a low pressure turbo, use the
lowest octane gas available. Most NA cars adjust and are designed to use the
lowest octane gasoline. Turbos are different since you have a much higher
compression, you need detonation resistance. I have a Viggen with a high
pressure turbo. I use 92 octane all of the time because without it, the
computer will most likely retard boost. On every other car I've had that was
non turbo, there was never any benefit to using high octane. Every once in a
while I get knocking in a Pontiac and at that point I will put Super in and
the problem is gone.