Effect of fuel octane number on FE

[aerohead]

Originally Posted by hummingbird

Phew! Guys, that was some colorful analysis!

I am somewhat OK using premium fuel for the sake of FE as the difference in prices is actually closer to ~40c. The questions are, will full premium boost FE or simply increase chances of engine foul up? Will a blend be better? What ratio?

My ambient temp is on the rise gradually and would be anything between 90 to 120 deg. now for about 4 months. Having to haul kids and stuff in the heat of the summer for leisure activities is not helping either, and probably is going to pull me below 50 mpg for this tank. But one does not lose faith or enthusiasm so soon, after getting such spirited support! Keep it up guys!

hummingbird,my thought now,is that there are so many variables in your driving environment,that even if the fuel could alter your cars performance,it would be lost in the scatter of all these other variables.Seems like it would almost require a laboratory environment to sort it all out.I don't think premium can foul anything but your purse,if the car will operate satisfactorily on a less expensive grade of fuel.

[hummingbird]

Aero, thanks for the assessment. my earlier two tanks had completely identical driving environment and the only two factors differing were the temperature and the fuel grade. That prompted me to ask.

However, I will build some data up by switching between 87 and 93 using 3 identical driving environment tanks each, so I get an idea.

Thanks guys for all the help!

[mwebb]

unmentioned so far in this thread is the fact that if premium fuel is used , where regular fuel is specified by the engineers who designed the system .
the fuel will not burn completely and there will be carbon deposits deposited inside of the combustion chamber .

which will result in additional as of yet UNmentioned problems .

and
the knock sensors and the feedback systems they are a part of operate in real time real fast . and they operate per cylinder .
so you can have knock retard values at the same time in different cylinders that have different values based on the conditions in those cylinders at the time .

the systems are designed to maintain Ignition timing at the optimum value at the time for each individual cylinder .
imho , there will be zero benefit to tampering with them.

i have graphed it and logged it on many different systems chasing problems
.....................................
bottom line ;
premium fuel does not improve FE in systems that are designed for regular fuel .