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Old 10-02-2012, 12:06 PM
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What grade of fuel do you use?

Now having just shy of 1,000 miles on my Wk2 I have noticed this car is very temperamental when it comes to the octane of fuel it is given.
When I bought the car from the dealer, they of course put the regular 87 gas in it... I could tell right away all it wanted to do was go slow and get into MDS ECO mode as fast as possible.

From then I tried mid-grade (89 octane) which felt to have spruced the cars performance a tad. Still however it wasn't all there.
Now 2 gas tanks later using only premium (91 octane) and my god this thing is a jeep on speed pills! It is very fast, has no problems climbing up the rpms (whereas before it felt to struggle.) ECO MDS hardly turns on (THANK GODDDD!)

- In addition, the drivetrain seems much more improved; gear shifts, shift points, rpm climb, and transmission shifter seem butter smooth.
So with all this said, what are your opinions? Is it a proven fact, or is the snake oil getting to my head?

Some technical data: WK2 5.7 HEMI, 4x4, bone stock.
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Old 10-02-2012, 12:10 PM
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Re: What grade of fuel do you use?

Let me also add, I live in a very hilly area.

The majority of my commute is driving up and down hills.

91 octane is also the highest grade available in the California market (unless you go to a race track or VP gas station).

90% of my driving is city driving ranging from 35-55 mph. Factor in hills, and MDS is the biggest nightmare a man could have... especially when a RAV4 passes you like your walking.
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Old 10-02-2012, 12:11 PM
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Re: What grade of fuel do you use?

I typically alternate between 87 and 89.
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Old 10-02-2012, 12:14 PM
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Re: What grade of fuel do you use?

Higher octane will allow the PCM/ECU to use more ignition advance. This results in higher efficiency and more power.

The catch is that there is a limit to how much ignition advance the PCM/ECU will use. The lower octane fuels are more volatile and actually have slightly more energy per a given amount.

So basically using a fuel with a higher octane than the manufacturer suggests is a waste because they didn't program the PCM/ECU to take advantage of it and it has slightly less energy.

The recommendation for the hemi is 89. So I generally fill up with 89. I will on occasion fill up with 93 just in case my fiancée put some 87 in it or some yahoo gas station had 87 in the wrong tank.

The fuel should have no effect on the shifting. The only effect I could see it having on MDS is if it was low octane and your knock count was so high that the PCM/ECU wouldn't allow MDS.
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Old 10-02-2012, 12:34 PM
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Re: What grade of fuel do you use?

My experience was that the V8 performance steadily improves with miles regardless till somewhere between 5000 and 10000 miles where it seems to level off. I think the V8 performance varies more with fuel ethanol content than octane rating. On my recent 2000 mile road trip I happened to get a couple tanks of fuel better than the usual, mileage went up to 21-22 mpg in speed up slow down interstates and it ran smooth as silk for those tanks. I don't think octane is going to effect performance as much, unless the ECU starts pulling timing due to a possible pre-detonation event. This is less likely when using 89 octane than 87 octane. Rare at 89 octane, even rarer at 91. But there seems to be more fuel quality variations from station to station and time to time that affects performance more than the difference between 87 and 89 octane. I use the recommended 89 octane as I find my V8 has a tendency to stumble when running 87. Your milage may vary
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Old 10-02-2012, 12:49 PM
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Re: What grade of fuel do you use?

If you have the V6 87 is all you need. Anything more is like throwing dollar bills out. The Hemi recommends 89 for Ultimate performance. I put 89 in the Hemi.
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Old 10-02-2012, 01:52 PM
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Re: What grade of fuel do you use?

I only use 87 octane. No performance complaints at all and I'm not really interested in turning my Jeep into a rocket ship. As someone mentioned, where I do see a difference is quality between certain stations as well as the Ethanol effect. The Shell, Costco and Wawa gasoline I use the most seem to work the best; off brands are hit or miss.
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Old 10-02-2012, 01:59 PM
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Re: What grade of fuel do you use?

Straight Shell 89 for my HEMI.
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Old 10-02-2012, 03:23 PM
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Shell 89 seems to work the best for me. I've been tracking every fill up since new and noticed some brands are not as smooth with the MDS. On a recent fill up from a Mobil station with 89 the MDS seemed real moody for a couple days. I believe it's from the recent switch to winter blend fuel in my area though.
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Old 10-02-2012, 04:03 PM
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Re: What grade of fuel do you use?

The owners manual for my 2012 Overland V6 says to use 87 octane, so 87 octane is what I use. Drives like it should, I guess.
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Old 10-02-2012, 05:34 PM
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Re: What grade of fuel do you use?

Shell V-Power since day 1
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Old 10-02-2012, 06:13 PM
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Re: What grade of fuel do you use?

89
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