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Old 11-27-2014, 08:14 PM   #11
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Indy I would agree with you years ago but in a modern engine the computer can adjust many parameters to reduce the pinging before you are even aware that it is happening. This can reduce the amount of power the engine makes. In a turbo it will reduce the amount of boost.
Yep!
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Old 11-27-2014, 08:29 PM   #12
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I remember having a debate with a couple of friends a while ago about Octane vs MPG. So, I sat down one day and figured out that based on the price difference I needed to achieve something like +0.5 MPG better using the premium over using the regular to make up the difference in cost (at the current prices that day). Now, that doesn't sound like much but considering I'm only getting about 8-9 mpg towing that's a significant percentage difference.

Now on the other hand though, my very first car only got Petro-Can Super Clean Premium. It was an old 89' Aries that had been sitting for a while and had developed fuel issues. Only that particular brand of premium could be used without causing engine knock. A cheaper grade and/or a competing brand that didn't have whatever the super clean agent was would just turn into issues for me.

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In the Ram with the 5.7 it says to use 89 for the best performance. With mine I tried using 89 and 87 while towing and I did not notice a difference, but my trailer is so light I don't need to use a lot of throttle to get going. My VW says to use 91 min so I always use the high octane in it.
I'll have to double check my book. My Ram with the 5.7 just says to use regular, so it gets the 87.
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Old 11-27-2014, 10:21 PM   #13
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I remember having a debate with a couple of friends a while ago about Octane vs MPG. So, I sat down one day and figured out that based on the price difference I needed to achieve something like +0.5 MPG better using the premium over using the regular to make up the difference in cost (at the current prices that day). Now, that doesn't sound like much but considering I'm only getting about 8-9 mpg towing that's a significant percentage difference.

Now on the other hand though, my very first car only got Petro-Can Super Clean Premium. It was an old 89' Aries that had been sitting for a while and had developed fuel issues. Only that particular brand of premium could be used without causing engine knock. A cheaper grade and/or a competing brand that didn't have whatever the super clean agent was would just turn into issues for me.
That would only work if you actually did get better mileage from using higher octane fuel, which you can not.
The BTU content is the same so it is impossible to achieve better mileage.
Most likely, that whipped Dodge aries had some serious mechanical issues and was out of wack on timing, beyond what the PCM could correct and the only way to prevent pre detonation was to use high octane fuel. The higher octane chemically slowed down the combustion burn which eliminated the rattle. You probably had a knock sensor that was inop as well. I am also guessing you had a constant "service engine soon" light on?
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Old 11-27-2014, 11:19 PM   #14
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That would only work if you actually did get better mileage from using higher octane fuel, which you can not.
The BTU content is the same so it is impossible to achieve better mileage.
Oh, I agree, but they didn't believe that so I did the math assuming that you'd have to travel just as far one one gallon of premium, as you could on the 1.x gallons of regular you can buy for the same cost. It worked out (at that time) that I'd need about an extra 0.5 mpg in order for that to be true.

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Most likely, that whipped Dodge aries had some serious mechanical issues and was out of wack on timing, beyond what the PCM could correct and the only way to prevent pre detonation was to use high octane fuel. The higher octane chemically slowed down the combustion burn which eliminated the rattle. You probably had a knock sensor that was inop as well. I am also guessing you had a constant "service engine soon" light on?

Nope, the engine light was usually off, unless I used a different brand gas. When the replaced the fuel injectors they told me the tank was full of sludge from sitting so long and they wanted me to drop and flush the tank (for about the same as what was paid to buy the car). Instead, since the super clean ran, I used that for the 2 years it had it before I traded it in on my 2nd (and very first brand new) car.



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Old 11-28-2014, 07:53 AM   #15
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I have to check my book but thought it said the engine required a minimum of 87 octane. My 6.0 l gets 87 octane.


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Old 11-28-2014, 08:20 AM   #16
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All good info. I'm going to dig out my truck's owner's manual and confirm what it says about which type of gas.
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Old 11-28-2014, 08:32 AM   #17
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From the manual : 5.7L Engine
This engine is designed to meet all emissions
regulations and provide satisfactory
fuel economy and performance when using
high quality unleaded gasoline having
an octane range of 87 to 89. The manufacturer recommends
the use of 89 octane for optimum performance.
The use of premium gasoline is not recommended, as it
will not provide any benefit over regular gasoline in
these engines.

Interesting that they even state that premium fuel will not help performance.
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Old 11-28-2014, 09:22 AM   #18
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Yep, I pulled out the book and sure enough, it says 89. Looks like I've been under octaning it for the last 4 years.

Oh well, no problems have arisen that I can see and since it does say 87 or 89 I don't think I've done any harm, but I'll have switch to the 89 for a little while to see if it makes any difference.




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Old 11-28-2014, 09:26 AM   #19
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My book says 87 acceptable 89 preferred for the 5.7. I guess I will start saving some money by not getting the premium.
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Old 11-28-2014, 09:27 AM   #20
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Having worked for the country's largest independent oil refiner for 41 years, I would like to share some of the knowledge I gained during that time. For the last 25 to 30 years of that time, one of my duties was setting up, maintaining and auditing the systems that inject the additives into all the various fuels; gasoline, diesel, kerosene and home heating oil, as they are being loaded for transport. Back in the days of leaded gas, many of the additives were primarily dyes. These days all gasoline, which of course is unleaded, is required by the EPA to contain a certain amount of IVD (Intake Valve Deposit) or detergent additive. Four automakers, BMW, General Motors, Honda and Toyota, feel that the current EPA minimum detergent requirements do not go far enough to ensure optimal engine performance, but there is a minimum required. Side note, there was one customer, which is a large and well known convenience chain in PA, did pay for an extra percentage of IVD, but after several years cut back to the standard minimum required amount, which is referred to as the LAC or lowest additive concentration.
Gasoline of different brands can and does come from varying sources. It is called the exchange. Over the years I worked on injectors for Mobil, Exxon (prior to those two merging) Sunoco, Shell, Gulf, Atlantic and BP. The refinery I worked for has its own brands,primarily KwikFill. Occasionally technicians from the various companies would come in to check their systems and at those times I would work with those techs. During one of those visits, the Exxon tech. told me that other than the required IVD content, their additive contained a proprietary chemical element the purpose of which was a fingerprint for their gasoline. Exxon had a lot of independently owned service stations and occasionally owners would buy gasoline off the black market to sell under the Exxon brand. The "fingerprint" allowed them to catch these owners.
Anyway, excuse the rambling, the previous comments on octane are correct. If it is not recommended for your engine, you are wasting money. As far as the 89 octane goes, it can be hard to find in some areas and it was never refined at the refinery I where I worked. I will not swear to it, but I would bet that most 89 is "made" the by the same method. It is splash blended. Meaning a certain amount of 87 octane is loaded into the compartment and then the amount of higher octane, 93.5 in the case of the refinery I worked at, is added to raise the 87 to 89 which here is called mid-grade.

Hopefully a few of you find this interesting at the very least!
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