Regular gas vs. Premium - Page 2 - Dodge Challenger Forum: Challenger & SRT8 Forums
General Maintenance Discussion This sub-forum is for the discussion of general maintenance of your Challenger such as oil changes, coolant maintenance, brake pad replacement, differential fluid changes, alignments, air filters and everything else to maintain your ride.

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post #11 of 20 (permalink) Old 05-11-2019, 07:39 PM
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Thanks for the advice I'm sticking to premium.

Forgot that while I wanted to make it clear why premium is important to use the flip side is it is only important, can only provide the intended benefit, provided the engine is designed for premium.


I didn't stress this in my previous post. Let me do so now.



There is little benefit in running 91 in an engine designed to burn 87 or 89.



With a couple of possible exceptions.


One exception could be if you track the car, a higher octane provides a bit extra margin against detonation so the engine controller won't have to retard ignition. Engines as they are used can have their octane requirement increase a point or two and this and what the engine experiences on the track could require a higher octane.



Another exception might be if you were heavily loading the car with passengers and their luggage or towing a trailer. I have no observations though to back this up but just knowing the engine is going to be working harder and could encounter operating conditions in which the engine cylinder filling exceeds what it has ever before the next higher grade of octane could be called for. In this case the higher octane gasoline provides a bit extra margin.


But except for the above exceptions if the engine is designed to run with 87 or 89 then using a premium grade of gasoline is ill advised. It wastes money mainly.


Be sure you buy gasoline from a busy station. Premium gasoline, especially, goes stale and quicker than the lower octanes of gasoline and if you fill up you want the freshest gasoline for your money.
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post #12 of 20 (permalink) Old 05-11-2019, 08:33 PM
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Best way to see if going to higher octane benefits your vehicle, get a diablo sport trinity and log knock. If you see almost no improvement in ST knock from 91 to 93 then just run 91. On a 6.4 or a (5.7 with a manual trans) stay at or above 91.


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post #13 of 20 (permalink) Old 05-11-2019, 09:07 PM
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I have a 2017 scat pack which recommends using 91 octane just wondering if there's really any difference between using regular and premium?

Your 6.4 Hemi has a 10.9 : 1 compression ratio. Stay with the highest octane you can find. 91 minimum. Maybe your ECM will compensate for 89 but I would not count on that to protect a $10,000 engine.
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post #14 of 20 (permalink) Old 05-12-2019, 05:01 AM
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Best way to see if going to higher octane benefits your vehicle, get a diablo sport trinity and log knock. If you see almost no improvement in ST knock from 91 to 93 then just run 91. On a 6.4 or a (5.7 with a manual trans) stay at or above 91.
I found a local source of 90 octane non ethanol gas. Since it was not a top tier supplier I was skeptical but wanted to experiment with it. I was hoping to use it for drag racing by adding TORCO to bring it to the octane needed by my tune. I set up a gauge in the trinity to display knock retard. While it's impossible to read the values in the gauge it does flash green when timing is retarded because of knock. Well, the thing lit up like a christmas tree around 3.5K RPM. The logs showed considerable knock retard. Even with the gas bumped with TORCO to 1 octane point above my target octane for racing it still produced much more KR than top tier 93 octane ethanol gasolines bumped similarly with TORCO.

My advice is get 91 octane (93 if its available) from a top tier supplier for your Scat Pack.

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post #15 of 20 (permalink) Old 05-12-2019, 06:08 AM
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My Canam 1000 takes 93 and the single hose gas pumps ripping me off with the 1st gallon or so of 93 being mixed with 87, it pisses me off. My tank holds 10 gallons but I seldom put more than 6 to 7 gallons in it so I'm being ripped off with a mixture of 87 when I'm paying for 93 octane.
Just something to keep in mind so don't just top off your tank with 5 gallons of fuel.
My Canam is an off road vehicle so i have to fill it before heading into the woods so i have no choice of running my tank empty.

Many stations have a nozzle for each grade of gasoline. Maybe you need to find one and buy your gas from one?
In Texas I have yet to come across a top tier gas station with seperate octane fuel hoses. Diesel is the only designated hose. What state are you in where there are still seperate octane fuel hoses? Also most stations here the super unleaded is 93 a few have 91 but most are 93 here. 87, 89, and 93.

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post #16 of 20 (permalink) Old 05-12-2019, 06:51 AM
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In Texas I have yet to come across a top tier gas station with seperate octane fuel hoses. Diesel is the only designated hose. What state are you in where there are still seperate octane fuel hoses? Also most stations here the super unleaded is 93 a few have 91 but most are 93 here. 87, 89, and 93.
Marathon is the only brand I have seen that has separate hoses for each grade.
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post #17 of 20 (permalink) Old 05-12-2019, 07:05 AM
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Many stations have a nozzle for each grade of gasoline. Maybe you need to find one and buy your gas from one?
the majority of stations in NC / SC (I'm near the state line) have one nozzle for the three grades and separate ones for diesel.

The stations that sell Non-Ethanol gasoline will have a separate nozzle, but those are ~ 90 octane for those.

I tend to buy 15 - 16 gallons at a fill up, so that 93 octane fill up only has ~ 1 - 1.5 quarts of whatever the previous buyer diluting what I'm buying.

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post #18 of 20 (permalink) Old 05-12-2019, 08:22 AM
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Here in PA, I don't think I've ever seen a pump that only has one hose. They all have separate hoses for each "level" of gas.

EDIT: The more that I think about that, I may be wrong. Maybe I have seen some with only one hose... I'll have to pay more attention going forward! :-)

EDIT2: Now that I *really* think about, I think that *most* DO only have one hose nowadays (one for gas and one for diesel)! Man, it sucks getting old...

Last edited by jtrosky; 05-12-2019 at 08:30 AM.
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post #19 of 20 (permalink) Old 05-12-2019, 08:34 AM
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Here in PA, I don't think I've ever seen a pump that only has one hose. They all have separate hoses for each "level" of gas.

EDIT: The more that I think about that, I may be wrong. Maybe I have seen some with only one hose... I'll have to pay more attention going forward! :-)

EDIT2: Now that I *really* think about, I think that *most* DO only have one hose nowadays (one for gas and one for diesel)! Man, it sucks getting old...
Around here it is common practice to have one hose for regular/mid/premium and one for diesel. Athought there is now a separate hose for elevated levels of ethanol fuel.

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post #20 of 20 (permalink) Old 05-12-2019, 08:59 AM
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the majority of stations in NC / SC (I'm near the state line) have one nozzle for the three grades and separate ones for diesel.

The stations that sell Non-Ethanol gasoline will have a separate nozzle, but those are ~ 90 octane for those.

I tend to buy 15 - 16 gallons at a fill up, so that 93 octane fill up only has ~ 1 - 1.5 quarts of whatever the previous buyer diluting what I'm buying.

Well, if there is just one nozzle for all 3 grades of gasoline not much you can do.


But I believe like you mention the amount of gasoline left in the hose that can dilute the high octane gasoline with the left over low octane gasoline from a previous pump use is small. Even if it was one gallon -- which I'm sure it is not that much -- 10 gallons of gasoline, 9 gallons of 91, and 1 gallon of 87, works out to 90.6 octane. Sure not "91" but hardly the end of the world.


Years ago when I rode a motorcycle I picked up the "trick" from others of draining the gas pump hose after the pump shut off. The amount of gas I got out of the hose was very small, not even close to a gallon -- I wished it had been a gallon for this would have represented a large fraction of the motorcycle gas tank's total capacity (less then 3 gallons IIRC).


It was such a small amount I soon stopped draining the hose of its gasoline. Just wasn't worth it.
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