If the manual says 89 recommended, and 87 is acceptable, then my plan is to have my wife put 87 in for driving to work and grocery-getting etc. . . I will put in 89 when loading up or towing etc.

I tend to agree with the comments that putting higher octane then designed for is only wasting money. Vehicles have no way to sense the octane of fuel other than to push timing, A/F ratios etc. to the limits, if it knocks, then back off. Manufacturers are not going to design an engine for 89 octane, then put ECU coding in to "push to the limits", to test for octane, just in case 1% of population might want to run higher octane. . . ie. it is highly doubtful that putting 93 octane in a stock Durango will make it any faster.

I am not an expert, but did some tuning on past cars. This involved monitoring and logging timing, knock, A/F ratios, temps etc. . . actually watching real-time what is going on inside the engine. The engines were most likely to knock in two conditions: 1) when lugging at low rpm, like coming to hill, while in overdrive. 2) prolonged high heat, after a fairly long period of wide-open-throttle, like at the end of 1/4 mile run. . . . Running higher octane all the time is not going to help these situations, because in 1) an increase in throttle to overcome loss of power will most likely eliminate the knock anyway, and 2) how often do we do full throttle that long.

I think towing would be a situation where the extra octane would be beneficial. Things can really heat up when pulling a hill, or into wind. Heat increases the chances for knock. If the engine is designed for 89 though, I still wonder if 93 would help, even in this situation.

To summarize my opinion. . If stock, I plan to follow the manual.

 

It really depends on what "it" is. What do you need the extra performance for? Are you drag racing? Do you get really annoyed when someone else moves away from the light and gets stuck at the next one before you? Do you have an affinity for close up views of tail lights on the freeway? Does getting to 60 on that on-ramp .01 sec faster give you a big thrill?

What I'm getting at with some dry humor, is that no matter what car you're driving, the difference in performance based on gas type is negligible (if not zero), and in street driving where they don't give out prizes, there's not much use for even a bigger bump in performance. I'd rather take my 6 bucks and buy a beer when I arrive .2 seconds after you at the tavern. ;-)

 

I will be doing the same thing

Only if the person is just running errands, if they have a legitimate use for the power, then its not a waste of money.

It does constantly push the thresholds thats when it goes into closed loop.
I have done the same thing. But you should be also looking for the command and actual timing. If you look, you timing can vary +/- 10degrees or more from your called for timing. it can add or take away depending on if it knocks. Each manufaturer can set at how many degrees it can change from. That would be how it "senses octane" there is no octane sensor, but if your car feels a slight knock, it would pull timing. If it doesn't it can add timing to give you more power.

The reason you found knocks from your 2 situations is one because you increased your load when its chugging. Any map you look at will change the timing based on loads. If you are tuning, you load the engine, then pull timing where it knocks. The other is because the temperature of you engine has gotten so high that it will preignite because when you compress the AF mix, the compression creates a temperature spike and the mix pre ignites(knocks)

But I agree, you more than likely aren't going to run your car to that temperature anyways.

In that situation, since octane is a measurement for resistance to knock, then yes I would think it would help. However, you ECM can pull timing before it gets to that point anyway.

 

I just finished scanning the entire manual because I just purchased my D and wanted to know everything Chrystler wants us to know. I thought it would be good to share what's in the manual.

Reference Section 5 of the manual, pages 545-552. http://www.dodge.com/en/owners/manuals/

89 is the recomended grade fuel, premium fuel is expressly NOT recommended.

As for brand, on page 552 there is a blurb about using Techron but it's only needed if switching between E-85 and regular fuel which is an issue for the V6 only. Also brands using MMT should be avoided - looks like this is used more in Canada then in the US...

As for me, I'll be using 89, weather it be at a top brand nearest to me or at Costco by mixing my own 87 & 93 together. I go for convenience, if it's a dumpy looking station I don't want to go in for coffee or any snacks and have to make a second stop therefore not convenient. I love the larger Shell or Texaco stations near where I live and will use them most.