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Discussion Starter #1
So in my prior thread I wrote about sputtering, occasional stalling and rough idle. I attempted to remedy it by putting in 91 octane gas.

I know there was a lot of discussion about octane rating and its affects on performance.. and with due dilligence I read the entire 8 pages on this forum, 12 or so pages in the Magnum forum and talked to my service advisor. None gave me any deffinitive answers so here is my experiment and results:

*** warning***
My experiences, described here, are my own only. This descripion does not purport to give advice nor technical assitance, nor is this approved by Daihmler-Chrysler Inc. in any way.

I had put in 91 octane and immidiately felt sluggish performance. The knocking and rough idle did not go away, if anything they became worse. Off the start the car seemed to be struggling, the usual accelaration was not there and other then the sluggish perfomance I felt no benefit.

When the tank went empty I filled it with a good 89 gas (good being not the el-cheapo gas station or Costco gas I usually put in the car). I used Chevron premium 89.

Immidiately upon starting the car I noticed that rough idle was gone. The car became buttery smooth, no sputtering, no rough idle. Accelartion was back in full force, no hesitation, no problems. The car just felt like it came alive.

Mind you no scietific evidence of this can be provided other then my over abused butt dyno, but I know that from now on I am putting quality 89 premium. No more experiments with higher octane for me :)

Thanks.

-Paul
 

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All the same?

OCtane rating refers to the RON = Research Octane Rating
Essentially, it is that grade of gasoline's resistance to ignition.
The higher the RON, the more resistant the gasoline is to exploding.
The reason that is important, is that in high compression motors - you don't want the gasoline to explode "prematurely" - causing damage to the piston, and rods/bearings.
The hotter a motor gets (summer, etc) , the worse the "problem" can become.
Motors nowadays are very finely tuned - I say stick with 89.
Too much RON and you might not get "full" performance either.
Not sure this makes sense? See here:
http://www.petro-canada.ca/eng/prodserv/fuels/6823.htm
http://www.repairfaq.org/filipg/AUTO/F_Gasoline6.html
 

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I wouldn't call 89 "premium". I have found that the brand (formulation of additives and such) really does make a difference in performance. In my area Chevron runs well, Exxon stinks. Have not tried discount brands, not worth the 2 cents a gallon less.
 

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Discussion Starter #4
Well, i know about RON and how octne ratings work and the different grade of gas, but I am just sharing personal experiences on the subject.

While 89 may not be "premium" (its called that in California, We have Premium, Supreme and regular), Chevron certainly seems to be better then the other ones so far. In my other cars I have never noticed any difference like this between gas grades and brands.

In Northern California, there are but 2 or 3 gas stations that sell anything over the 91 grade... so I can't really compare.
 

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Chevron 89 is the gas I have been using since I got my car in August, except for the occasional emergency fill-ups at other stations such as Arco or Shell. Car runs smooth as silk. No rough idle or hesitations.
 

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Thanks for the update SLK, good info. I'm glad the problem was cleared up, with the better quality fuel.

If anyone runs their car really hard or the intake temperature goes up, the octane rating might need to go up. Sea level (more octane) ver. higher elevations, as well as other factors. Loading the engine in the MDS mode for long periods of time might benifet from higher octanes.

Higher octane fuel will let the engine run more advance, and probably more peak horsepower. Lower octane will probably retart the timing to prevent spark knock. Retarted timing will usually give more torque at lower RPM's, which will make the car feel faster. Retarted timing sometimes causes a decrease in fuel mileage. Running a free flowing exhaust (like my Borla) or using a chip, will change requirements.

Anyways, if the gas has enough octane rating to keep the engine from knocking, everything should be fine. Just remember that as the seasons change, you may have to re-eval your requirements.

I may just have to take my own advice and give 89 another chance. Chevron like Joey is using, with a tank full of extra detergent Shell preminum just to keep things clean, every now and then. :)

I may check the 20 to 60 MPH times out, to see if there is a change. I don't think the Chrysler should mind. :eek:

Dixie
 

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Just ran out a tank of 92 octane and refilled with 89. My rough idle was back, in less than 10 miles. My car is just spoiled, Wild Turkey or nothing.

Dixie
 

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jeepgrady said:
I would never use a non-name brand fuel in any of my cars.
I only run brand X petrol, C, X5 etc. Speedway, Wal-Mart Fuel Mart for many years and I have only had one problem not related to brand though. The Alfa got some water (could happen at any brand and has when I only ran brand name petrol) one bottle of dry gas and problem solved. I use to be a brand only guy and for the last 15+ yrs have used exclusively brand X for a few hundred thousand miles. I lived in CA for a year and they have some weird grades and formulations. I use 89 only in the C, the X5 called for 93 and ran perfect on 87.
 
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