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Discussion Starter · #1 ·
I lost my job and I am going to be selling my Predator and the AFE CAI!

I have almost a full tank of 91 since I run the 91 tune is it ok to revert back to stock and un-marry predator so I can sell and ship but still run the 91 octane in the car until its empty and then go back to the recommended 89 octane for stock?

Thanks for the help guys!
 

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absolutely not, drain the tank and send the gas to me :grin:

you'll be fine. You'll get a hair better gas mileage and your car will adapt ignition timing as it needs. It hurts nothing
 

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Discussion Starter · #3 ·
absolutely not, drain the tank and send the gas to me :grin:

you'll be fine. You'll get a hair better gas mileage and your car will adapt ignition timing as it needs. It hurts nothing

But when that tank of 91 is done go back to 89 for sure correct?
 

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But when that tank of 91 is done go back to 89 for sure correct?
Your 3.5L is designed to run on 87 or 89. If you are not into it really heavy, and even if you are, with the stock tune you will be fine as the speed density system will adjust for injector pulse width, timing, and spark curve.

Sorry to hear you lost your job. I hope you find somethng soon.:)

Regards,
Brian
BND Automotive LLC
440-821-9040
 

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I've been running 91 on my rt for like 10k miles now with no pred and it's fine.
 

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No reason to run 91 in a stock hemi. Save your $, run 89.

JK
 

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higher octane will have slightly lower gas mileage. It produces less Btu under identical conditions. Where higher octane pays off, is if you can tune to take advantage of the slower burn. Higher octane won't hurt a thing, except as stated above, slightly (and generally unmeasurable) lower gas mileage.
 

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i've always achieved better gas mileage on higher octane however its not enough improvement to warrant the extra cost of .30 cents a gallon
 

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Discussion Starter · #9 ·
Since I'm back to stock Should I just run 87 or is it better to run 89 in my 3.5L?
 

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Since I'm back to stock Should I just run 87 or is it better to run 89 in my 3.5L?
run the recommended fuel grade. Any higher will result in lower gas mileage. Higher octane fuel has lower energy per gallon then lower octane.
 

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Discussion Starter · #11 ·
Is it true that the recommended octane for the 3.5L HO V6 is 89?

If so what is the advantage to 89 and 87 and if none why d they recommend 89 then?

Thanks for the inof guys.... just wanting to see if doing 89 is really worth the extra dollar 60 or so bucks!

run the recommended fuel grade. Any higher will result in lower gas mileage. Higher octane fuel has lower energy per gallon then lower octane.
 

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Is it true that the recommended octane for the 3.5L HO V6 is 89?

If so what is the advantage to 89 and 87 and if none why d they recommend 89 then?

Thanks for the inof guys.... just wanting to see if doing 89 is really worth the extra dollar 60 or so bucks!
higher octane has a slower burn rate, which allows the spark and/or compression to be bumped to generate increased power.
 

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Here is a test someone did with a Jeep Liberty.You can see the 89 gave the best results.

Octane Rating vs. MPG, Test Results
Many people believe that higher octane gas gives them more power and mileage. Some argue the gain in mileage isn't worth the additional $0.10 - $0.20 or more per gallon compared to regular 87 octane.

I decided to put this to the test, MPG only. I had zero desire to pay and have this thing dyno tuned with different gas, not even an option.

The results are pretty much what I expected. Over a test period that was 20 fill-ups long, 87 and 89 octane were pretty much an even match, and premium (92 or 93 depending on station) the MPG went down slightly. I felt ZERO difference in power, smoothness, or any other drive-ability changes between the octane ratings.

I feel there was an even mix of all driving types for each octane rating.

The Liberty has a K&N intake on it, which was the same for all tests. Stock computer (no chip), stock exhaust.

If you removed the 2 tanks with comments next to them, the results would be even more clear: Higher octane on my application hurt mileage.

Discuss!


87 octane
Miles Gallons MPG
322 17.5 18.4
236 12.7 18.6
296 15.8 18.7
277 16.7 16.6 idled with A/C for approx 3 hours this tank
266 14.4 18.5
152 8 19.0

87 Octane totals
1549 85.1 18.2


89 octane
Miles Gallons MPG
270 14.8 18.2
294 16.4 17.9
298 16.5 18.1
307 16.4 18.7 ALL highway miles
220 12 18.3

89 octane totals
1389 76.1 18.3


92/93 octane
Miles Octane MPG
241 12.9 18.7
244 13.5 18.1
278 15.8 17.6
217 12.2 17.8
246 14.1 17.4
127 7.6 16.7
262 14.34 18.3

92/93 octane totals
1615 90.44 17.9


Grand total
Miles Gallons MPG
4553 251.64 18.1
 

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I log every fill up and track my MPG and miles driven. I have used both 87 & 89 and didn't notice any difference in mileage. I run 87 oct. now at every fill up.
 

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IS there any proper procedure to switching? Or is it just drive til your empty and switch?
 

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Discussion Starter · #17 ·
Was wondering this too!

I have 91 right now cause of the predator removal, Do i just jump to 87 and the car will adjust accordingly?

IS there any proper procedure to switching? Or is it just drive til your empty and switch?
 

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Yes, you can switch right back to 87 with zero problems. And the 91 in your tank now will also cause zero problems.
 

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