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Discussion Starter #1
Gas prices have gotten so high I think I need to go from 93 Octane to 89..
I have the 91 setting on my Flashpaq...What would be the effect of using 89 octane with the 91 setting?
 

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I have flashpaq as well. I would think if you install a 180 degree thermostat you might be able to get away with it. if you can keep the engine cool enough so as to not get preignition as you would get with low octane gas in a car tuned for high octane gas you'd be golden. And I guess that would also depend on how hard you ride her in everyday driving. I would think if ya put in the 180 therm and didn't ride her hard all the time you could get away with the 91 tune on 89 octane.
 

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I would not risk it; the 91 setting may advance timing too far or too quickly using 89 octane gas. If you are not going to use at least 91 I would change to the 87 octane setting on the flashpaq; you can still enjoy the much improved transmission settings that way.

But how much are you really going to save by lowering gas grades? I too am feeling the pinch of gas prices, but it's all grades not just premium.
If you drive 15,000 miles per year (about average) and average 17 mpg, you are going to use 880 gallons of gas per year. If the difference is 20 cents a gallon then you are only going to save $176 per year or less than $15 a month!. I realize that 15 bucks here, another 15 bucks there, can really add up if you're not careful but I'd cut that 15 bucks someplace else.
 

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Some folks claim that they get better mileage running the 91 tune, and their net out of pocket gas expense is about the same.

Personally I wouldn't run 89 on the 91 tune. Not worth the risk of engine damage.
You have to worry about engine knock running 89, especially on hotter days. Unfortunately Flashpaq's knock retard data logging does not work. If it did work, you could run 89 and see how much knock retard was occurring. Flashpaq's Knock Sensor data logging does work. You could try comparing the Knock Sensor readings on 91 octane and 89 octane. Higher Knock Sensor readings with 89 octane, compared to 91 octane, would indicate your car is not running as well with the 89. You can also data log timing advance to see if any timing is being pulled during the high Knock Sensor spikes.

Here is an example of a data log with knock sensors and timing advance displayed together with 91 octane.
 

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Discussion Starter #5
Good point Kevin, I knew what I was getting into when I got the Hemi... And nice writeup joey... Anyone know what the performance difference is from using 87 octane or 93 octane?
 

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Good point Kevin, I knew what I was getting into when I got the Hemi... And nice writeup joey... Anyone know what the performance difference is from using 87 octane or 93 octane?
This pic shows some dyno stock runs, with Superchips, and other mods, but no runs with 93 octane. Can't get 93 octane in California. These runs were from the Great Intake Face Off(GIFO) posted on the lxforums.
GIFO4 - Perf Results, Analysis, Comments and Meet & Greet Pics - LX Forums Modern Mopar Muscle

Test 5 and Test 6 compares Superchips 87 and 91 octane.
91 octane average HP increased 6hp, from 271 to 277. I would guess the 93 octane might add another 5hp.

What is interesting, and discouraging, is Superchips performed worse than the stock run, Test #2. Stock average HP on Test 2 was 286HP, almost 10hp higher than the 91 octane in Test 6.

 

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Holy crap dude! Great job! Learned somethin new today.
 
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