:>:> Is there any advantage of buying 93 octane over 91?
:>
:>: Only if it pings on 91.
:>
: Guys, this DEPENDS ON YOUR CAR! Audis (and most other cars in
: this cross-posting) built in the last DECADE have knock sensors
: on the engine. When any 'ping' (the most correct term is
: 'premature detonation') is detected, the timing is retarded.
: Because this is almost instantaneous, YOU will never hear it.
: But you WILL feel it because retarded timing produces less power.
: It may be that there is no difference between 93 and 91 octane
: fuels, but then again, there may be. You'll have to be the judge
: and it will depend on what you're driving and how you're driving
: it.
I wonder if this retarded time is what causes E34's 6cyl engine to act
boggy when taking off at the light occasionally. I've read other
posts by other people about this before. I get 34mpg on the road if
I drive 65 in the winter so i'm not complaining about fuel economy.
Regarding the quote above... My 525i gas cap states a minimum AKI 89 fuel.
I'm not sure if that is the same scale as the octane rating that I'm
accustomed to seeing at the pump. I know there are several different
scales used for measuring octane ratings.
My concern with premium fuel has always been that not enough of it sells
at the pump, and consequently may sit in the tanks at the station for
long periods of time. I wish I had a litmus-type tester for fuel so
I could tell the true octane rating of the fuel, its quality, moisture
content, etc. I get a little jittery when I fill up and notice the
87 octane pump looks like it had pumped billions of gallons while the
premium 93 octane pump looks like it has never been used before.
I haven't done enough driving with different octane ratings of fuels
to judge if 91 beats 93 in my car but the extra price is worth it to
me if I will prolong the life of the engine.