hi there are some urban myths regarding fuel etc
here is what i know and my experiences
service station brands often share their fuel and facilities, so you may find shell optimax could in fact be the same physical fuel as Mobil 8000
and likewise, you may find Caltex Vortex 98 is the same as BP 98 - not all brands have local facilities in each state, so they share in some parts
occasionally there are bad batches of fuel, whether they are stagnant in the tanks at the servo, or just crap batches
i believe this happens in all brands, ive had a full tank of shell 98 optimax detonate its ass off in my well tuned GTST
reproducible denotation over and over with that tank, put in another tank and presto no more detonation
i would suspect all brands would have this issue form time to time
using higher octane fuel in a car thats not tuned for it usually give you no benefit other than reduce the lieklyhood of detonation
people often try 100ron V Power Racing on a stock ECU or a base tuned ECU and go "nah it didnt do anything, what a rip"
of course it wont do anything, you don't gain magical powers or more "killowatts" by adding in more octane.
you need to "tune" the car once you have higher octane fuel in the car, that is, add more timing where the engine can handle it
with higher octane fuel, the car can handle more timing (usually)
so more timing, usually means the engine is more efficient, usually means more power / response.
there are myths about ethanol based fuel, melting fuel lines, blowing up pumps, melting pistons
voiding warranties etc, if you are in doubt dont touch it but ive been using it for 3 months now with no other issues
other users have also reported the same results. if it was to melt fuel lines etc it wouldn't be available at the pump at local servo
a common known good use of 100ron in the wild are track days for guys with aggressive tunes
the extra octane count adds as insurance, last thing you want is detonation on a track day, the extra octane is your insurance
if the car is tuned on 98 and you run 100ron the chance of detonation is significantly smaller, than using 98ron
another known good use of 100ron is as a detonation killer -thats how i use 100ron at the moment
my car is tuned on 98 premium with an aggressive as all hell tune, 50deg on the IGN map in some areas
with 98 ron in the car and summer intake temps of 40deg and an exposed pod if I load the car up
and say floor it there is some detonation, increased intake temps will usually cause that
so by putting in 100ron there is very little detonation. under aggressive load and intake temps most knock you would see would be maybe 15 at the most
with 98 ron in the car and the same conditions it would be typical to see maybe 50+ of detonation on the powerfc hand controller
some may argue that the car isnt tuned properly if it does this, that would be debatable and i could go back and retune it with simulated ambient temps etc and take out some timing to handle all aspects of the summer/winter range etc but its also easy to just put in 100ron and away you go
there are lots of 'maybes' and 'yeah for sure' regarding octane and brands and fuel economy
ive heard them all from workshops, today tonight's specials on fuel etc etc etc
i dont see how mathematically one fuel will give you more milage than another brand
prehaps im dumb or missing something - but i dont see getting more KM's to a tank on BP98 vs Caltex Vortex etc etc