Hemi 6.4, gasoline. 87 or 89.

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JS4024

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87 has always worked fine with my 6.4, and my Jeeps 5.7. It’s like the folks who say using a cold air intake gives a huge power boost... Not so... The higher octane prevents pre ignition and yes that can rob some power, but the engine controller will change the timing just a bit to compensate when it detects detonation. Just let the computer do what it needs to do Save the money. Quality 87 octane is fine.
 
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Iron Outlaw

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Honestly, and it could be in my head, mine feels different now that I leveled and have 35s. Before I really couldnt tell a difference. Now the truck struggles some in the midrange when accelerating normally and it seems more dramatic when I run 87 vs 89. At wide open throttle, which I hardly do, I cant tell a difference.
 
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Rwgarrison23

Rwgarrison23

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Well, it took me 2 weeks to test 87 and 89 from empty to full. I used the lie o meter for rough guess. I get better gas mileage using 89 with same mileage I did back and forth to work and home only. I gained about 1.5 mpg by using 89.
 

RoadRamblerNJ

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87 has always worked fine with my 6.4, and my Jeeps 5.7. It’s like the folks who say using a cold air intake gives a huge power boost... Not so... The higher octane prevents pre ignition and yes that can rob some power, but the engine controller will change the timing just a bit to compensate when it detects detonation. Just let the computer do what it needs to do Save the money. Quality 87 octane is fine.
Correct. I wasted an awful lot of beer money buying the highest octane I could find for many years. It was much more important in the 1970s. I ran some high compression sbc motors back then. Now, let the brain in the car figure what it needs.
 

SouthTexan

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I will share this again for those who want to know if running 89 is worth it to them. The top is the cost per gallon and the left is the miles per gallon.

As you can see, in most cases if you achieve at least a 1 mpg increase with 89 octane, then it would make up for a $.20 to $.25 cost per gallon difference of 89 octane because the cost per mile will be the same. So you are getting added performance and knock prevention for little no additional cost. Basic rule of thumb, for every $.10 increase in cost, you need to achieve an additional .5 mpg for the cost per mile to be the same.

Of course it is a different story if your mpg does not increase.

Cost-per-mile-2.png
 
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Marc Taylor

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My 5.9 struggles hard with this, as I drive short mileage (6 per day) and don’t run it hot enough. My mechanic, who is usually very in tune with this truck, recommends Premium always, but it runs like **** and fouls the plugs quickly at higher octane.

Love this truck. Want to keep it. But want it to run as good as it looks.
 

slacadjuster

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I filled up using both gasoline from Shell fuel. I ran 87 and 89. I dont know if it's me but truck seem to like 89 better. What is recommended gasoline for these 6.4? Mines a 2018, by the way.


Although I have the 5.7 in my Ram, in the owners manual, it states 89 recommended, though 87 is acceptable.....I've run 87 in it since I bought it new in 2015.....Never even a hiccup.
 

GsRAM

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Well, it took me 2 weeks to test 87 and 89 from empty to full. I used the lie o meter for rough guess. I get better gas mileage using 89 with same mileage I did back and forth to work and home only. I gained about 1.5 mpg by using 89.

At the higher cost of the 89 even with the higher mpg using it, are you loosing money or is it a wash?
 

Gr8bawana

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I filled up using both gasoline from Shell fuel. I ran 87 and 89. I dont know if it's me but truck seem to like 89 better. What is recommended gasoline for these 6.4? Mines a 2018, by the way.
The truck likes it better? It's all in your head. Just like people who say their truck runs better with clean oil or has just been washed. :manos:
 

crash68

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The truck likes it better? It's all in your head.

No it's not in his head. The 6.4 and 5.7 Hemi both recommend 89 octane fuel. Couple that with the fact they both use a feedback fuel system and detect spark knock. The engine ECM will not pull as much timing from the engine running the higher octane fuel especially when under higher loads.
 

GsRAM

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The truck likes it better? It's all in your head. Just like people who say their truck runs better with clean oil or has just been washed. :manos:


Agreed. As I said I feel no seat of the pants difference after multiple tanks of both 87 and 89 octane towing heavy and running empty. To each their own though....if you feel better about it run the 89. It's nice we can choose!
 

Chris1911

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Well, it took me 2 weeks to test 87 and 89 from empty to full. I used the lie o meter for rough guess. I get better gas mileage using 89 with same mileage I did back and forth to work and home only. I gained about 1.5 mpg by using 89.

Gaining mpg and being able to go a little farther on a tank of gas while towing would make me happy. Been using 87, but i'm going to give 89 a try for a while.
 
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