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89 octane on 91 setting with flashpaq???

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Old 12-11-2009 | 04:46 PM
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mighty-banana's Avatar
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From: Edinburg, TX
Default 89 octane on 91 setting with flashpaq???

Ok I got my new flashpaq and I've read all the great reviews about the 91 octane setting. So I finished my tank of 87 and went to the gas station. And WTF no 91 octane. We have 87, 89 and 93. Now my question is can I run the 91 octane setting with 89 octane or I'm I stuck at 87 or 93 octane. If location makes a difference I live in south Texas. Edinburg, Texas which is about hour and half from the gulf coast.
Old 12-11-2009 | 05:15 PM
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Fill your tank up with half 89 and half 93, problem solved.

I wouldn't run shy on the octane level as it will cause pre-ignition and pinging.
Old 12-11-2009 | 06:24 PM
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I run the 91 octane setting but use 89 octane. Hard to find 91 anymore. Been running it that way for about 2K miles. So far So good!!
Old 12-11-2009 | 07:02 PM
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Always safe to run a higher rating. Lower could result in preignition/detonation, but the 3.8 isn't the highest performance engine in the world... I doubt you'd cause any damage running one step lower.
Old 12-11-2009 | 07:04 PM
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My JK pinged on 91 octane on the 91 tune when I demo'd it, I wouldn't dare try 89 alone...
Old 12-11-2009 | 07:11 PM
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Nothing to add, just that I lived in Edinburg, TX for a year in 1999-2000. Great memories and awesome fajitas at Zarapes! I would have my top off all year instead of this -20 degree and snow business!

Sorry for hijacking the thread!
Old 12-11-2009 | 11:07 PM
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Jpop, what do you mean by I wouldn't run shy on the octane level as it will cause pre-ignition and pinging. And could I go half and half.

I also had another question could I run 87 tune with 89 octane or would that be a waste of money.

Also what setting would be go for highway milage taking a road trip.
Old 12-12-2009 | 06:31 AM
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I'm on my second tank of the 93 octane tune and I can't say it's any better than my 87 octane tune. It seems more "jumpy". It wants to rev to WOT much quicker than the 87 octane tune. All that's done is make my girlfriend car sick and me try to compensate. I'll be going back to 87 octane as soon as I burn this tank.

That being said I'm not running any other engine performance mods (intake, exhaust, etc) so that may be effecting my results.
Old 12-12-2009 | 06:50 AM
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I'm on the 3rd tank of 89 octane with the 91 tune. No pinging or other problems. Performance seems to be the same and mileage might be even slightly higher, but close to the same based on the 1st 2 tanks.
Old 12-12-2009 | 08:03 AM
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Originally Posted by mighty-banana
Jpop, what do you mean by I wouldn't run shy on the octane level as it will cause pre-ignition and pinging. And could I go half and half.

I also had another question could I run 87 tune with 89 octane or would that be a waste of money.

Also what setting would be go for highway milage taking a road trip.
If you run shy on the octane fuel you are running as compared to the octane setting of the programmer, you will start to run up against the knock sensors and retard your timing. If you are retarding the timing, you are taking away the benefits of running the higher octane tune. This isn't to say that it won't work, as the PCM will correct A/F mixtures but it won't work optimally.

My preference is to always run at the Tunes octane or higher. I don't want to droop any of the advance and I don't want the problems associated with running lean.

The half and half method works fine although it is a pain in the ass. Personally I would just aim high and forget about it.

Lastly, in my opinion and with the winter months, I always fall back to the lowest octane tune. I know because of how much longer it takes to get to operating temperatures I'm going to see a 10% hit in fuel mileage. Lower temperatures also reduce octane requirements and lower octane levels create more heat. That's why engines tend to knock more in the summer.

In round numbers, a 20 degree drop in intake air temperature reduces your octane requirements by 1. Of course the PCM takes care of most of this, but why would I dump a high octane, slow burning fuel in my tank when I can get a hotter/faster burning low octane fuel to go along with the cold dense air?



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