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Discussion Starter #1
The manual says 91 octane is reccommended; however, the one time I used this in my R/T Charger, it really seemed to muck up performance, the car seemed to be slower for several weeks. One service engineer at the dealership I spoke with said I should use the cheapest, most low end gas available and made a joke about mixing it with water (obviously not going to do that), on the other hand, the manual says use 91, but my experiences with 91 have not been pleasant.

What do you suggest?
 

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Might be you just got some bad gas that time your talking about....at any rate...there is a VERY good reason the higher octain is called for by Dodge on your car and the "tech" you quoted is clueless!! Here is a good read by one of our esteamed members on the Z from a while back.
http://www.challengerforumz.com/showpost.php?p=503037&postcount=33
Please note the imfo from about the middle down on this.
 

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As Friendoffur said you most likely got some bad gas, or some gas that actually had water in it. (In the past unscrupulous garages have been known to do this) I'd say you should run at least 91 octane but if you insist that you don't want to run 91 then run 92 or 93, but I certainly wouldn't run below the manufacturers recommendation.
 

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I have ran premium in the car from day one, this is what is recommended by the manufacturer. I know the computer will adjust etc. to octane level in the gas but why take a chance.

I am not trying to be an A$$$OLE or offend but you spent a good chunk of money on the SRT, gas prices should not enter the equation.

Just my 2 cents
 
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You bought a SRT and you are wanting to run low octane gas in it??????

Even when I run 93 octane in mine I still get some short term knock retard.

Don't even think about running regular gas in your SRT.
 

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Lower octane wont be an issue with casual driving, but if you are spirited then I would run 93 in her
 

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Another good reason to run 91 or better octane all of the time is because your computer does learn what your gas is doing over time. If you are running 87 or 89 octane it will continually retard the spark so that you will not be getting the performance out of your machine that is available. IOW, even if you have currently filled your tank with 91 or 93 octane but have been running 87 for a long time, your computer will use a program that is based on 87 octane. You won't get performance that you might expect out of your car for another 50 starts. My suggestion is to commit to running 91 or 93 octane and pulling the #2 fuse on your first fill up of the high octane gas. Even better would be if you can find ethanol-free gas at those octane levels. Try this link....http://pure-gas.org/
 

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Discussion Starter #9
Perhaps with my R/T charger, the reason why performance suffered was that the onboard computer had over time tuned the car based on 87 octane?

When I did fuel up the Charger on that stuff, it seemed to take about three weeks for it to return to normal performance. When I fueled it I hand-pumped it myself at a retail gas station, which if memory serves was the local overpriced Chevron. Also, if memory serves, Chevron has a very high ratio of MTBE compared to other retail gasolines; could that have been a factor as well?

I will observe that even with the 87 octane gas I have in there, the SRT is the fastest car I've ever driven, and seems to be faster than anything else on the road, so my main consideration would be avoiding maintenance problems as opposed to squeezing the last drops of performance out of the vehicle. My main reason for being hesitant about using high test was the unpleasant experience I had with it in the older R/T Charger, and the comment from the apparently moronic service writer.

Thanks for your help on this guys, I really appreciate it!
 

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Perhaps with my R/T charger, the reason why performance suffered was that the onboard computer had over time tuned the car based on 87 octane?

When I did fuel up the Charger on that stuff, it seemed to take about three weeks for it to return to normal performance. When I fueled it I hand-pumped it myself at a retail gas station, which if memory serves was the local overpriced Chevron. Also, if memory serves, Chevron has a very high ratio of MTBE compared to other retail gasolines; could that have been a factor as well?

I will observe that even with the 87 octane gas I have in there, the SRT is the fastest car I've ever driven, and seems to be faster than anything else on the road, so my main consideration would be avoiding maintenance problems as opposed to squeezing the last drops of performance out of the vehicle. My main reason for being hesitant about using high test was the unpleasant experience I had with it in the older R/T Charger, and the comment from the apparently moronic service writer.

Thanks for your help on this guys, I really appreciate it!
You sound like an open minded young man so I'll take some time to further explain why I believe....other than the manufacture telling you... why you should ONLY run priemium in your 392. The object here is to not end up with your car tore down at the dealership for who knows how long with pieces of a piston visable through the open throttle body. Yeah....they probably won't test the gas in your tank...and cover this under the warrenty...but will your car ever be the same if this does happen? Ask ANY engine builder....or read it ANYWHERE on line.....predetonation is the engine KILLER!!! What I think maybe is being overlooked here is the different conditions that you may encounter in your day to day life driving your 392. Yes...the PCM WILL retard your timing if and when it hears knock with the lower octain fuel....resulting in less horsepower. BUT...it DOES have its limitations on how much it can do this!!! There are a few things that can alter how much knock your engine might see. Having your car loaded with friends and your trunk full of stuff is one. Living and driving in an area with inclines..(mountains and steep hills) is another. Stuck in bumper to bumper traffic on a 90 plus degree day....or just plain driving in 100 plus temps like we get here in Texas. Remember....even though your cooling system is keeping your engine from overheating.....the incoming air fuel charge is whatever it is tempature wise....and DOES have a bearing on predetonation.
The vehical I had before my Challenger was a 04 Dodge 1500 regular cab with the 5.7 Hemi. On a trip to Iowa from Texas with my wife and a LOAD of boxes in the back that my son couldn't take when he moved to Iowa.....in Arkansas I encountered some steep up and down driving posted at 45 mph. The predetonation was BAD!!!!! If I had a loud exhaust or had had the radio turned up....I might not have heard it right away. I had to manually downshift to a lower gear till the first station I came to that I could fill the tank with premium gas. The point here is that the PCM DOES have its limitations on how much it can do to save your @$$ in certain situations.
 

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Discussion Starter #11
Just out of curiosity, what does predetonation sound like? If it occurs to any extent will it trigger any diagnostic alarms?
 

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Just out of curiosity, what does predetonation sound like? If it occurs to any extent will it trigger any diagnostic alarms?
The best way I can describe it would be if you took an empty tin can and put 10 or so BBs in it and shook the can. To the best I know...this will set NO codes!!!
 

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Discussion Starter #13
I don't believe I've ever heard a sound that alarming, just the normal soft purr on the R/Ts and the violent thunderous roar on the Yellowjacket.

I take the cars into the dealership when there's even the slightest irregularity. On the grey 07 R/T charger, shortly after I bought it I noticed an unusual feeling in the ride; I took it into the dealership, the cause of that feeling was apparently unresolved but they discovered the car had an unaddressed recall issue involving a defective transmission fluid cap, and replaced it (but the transmission fluid had not yet reached a critical level).

One weird incident occurred once when I was driving the same charger uphill at high speed, and an earthquake occurred. The check engine warning light came on; I took it into the dealership but they found nothing wrong and subsequently reset it.
 

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I don't believe I've ever heard a sound that alarming, just the normal soft purr on the R/Ts and the violent thunderous roar on the Yellowjacket.

I take the cars into the dealership when there's even the slightest irregularity. On the grey 07 R/T charger, shortly after I bought it I noticed an unusual feeling in the ride; I took it into the dealership, the cause of that feeling was apparently unresolved but they discovered the car had an unaddressed recall issue involving a defective transmission fluid cap, and replaced it (but the transmission fluid had not yet reached a critical level).

One weird incident occurred once when I was driving the same charger uphill at high speed, and an earthquake occurred. The check engine warning light came on; I took it into the dealership but they found nothing wrong and subsequently reset it.
LOL....NEVER underestimate the power of Mopar!!........I should have added that the sound is not real loud....as if you had pillows around the can of BBs as you shook it.:smileup:
 

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There is yet another reason to run the highest octane in your engine...The compression ratio of your pistons is in the area of 10.5/1. Lower octane gas is simply not an option in any of the new Hemis as it will cause detonation in low load situations.
 
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