Octane

[Curmudgeon]

89,and 90+ octane compared to 87 just allows the computer to allow slightly advanced timing,that makes the engine have just a little better performance,allowing computer to up the timing.And it may result in slightly better,maybe a mile or so fuel economy.But then premium/ midgrade costs more.87 wont hurt a thing.89 is a slight improvement.Up to you if it's worth it.I run mostly 89,cause I can

^User name checks out.

 

[HEMIMANN]

I you guys read the study by the member with a live datalogger, you'd all use 89 minimum.

The default ignition timing setting is advance for 89 octane gasoline combustion resistance.

The WAY ignition timing is relaxed for 87 octane gasoline is by repetitive detonations. That sound good to you? Not to me. This was shown on the datalog. Look it up.

 

[HEMIMANN]

Mine is. Says right in my book, "Use 87 Octane with no more than 15% ethanol".

Then they've changed something, if only the verbiage. My 2017 O&M says 89 octane is preferred, and 87 octane is acceptable.

See my post above for HOW they adjust ignition timing to account for sensing the combustability of the gasoline octane.

 

[Octane]

I you guys read the study by the member with a live datalogger, you'd all use 89 minimum.

The default ignition timing setting is advance for 89 octane gasoline combustion resistance.

The WAY ignition timing is relaxed for 87 octane gasoline is by repetitive detonations. That sound good to you? Not to me. This was shown on the datalog. Look it up.

Agreed,as my username implies "high" octane is better!

 

[HEMIMANN]

Agreed,as my username implies "high" octane is better!

Well, no, what is better is correct octane for the ignition timing and compression ratio. Too low and you get detonation. Too high and you get unburned deposits.

This is the whole point of the octane discussion. For those of us with Hemi engines that have 89 octane preferred, it's a dilemma because there is no such thing as pure 89 octane.

 

[Octane]

Well, no, what is better is correct octane for the ignition timing and compression ratio. Too low and you get detonation. Too high and you get unburned deposits.

This is the whole point of the octane discussion. For those of us with Hemi engines that have 89 octane preferred, it's a dilemma because there is no such thing as pure 89 octane.

Hi octane as in 89 compared to 87,in my post.Yes...and wouldnt want to run 100 octane anyway.Not needed.

 

[Octane]

I saw a video once,that showed a 650hp vette on a dyno, running premium octane fuel.It was putting
out those 650 horses too.Then they ran lower octane gas in it.The dyno eventually showed a 550 hp output on that fuel.Computers are smart

 

[Tulecreeper]

Then they've changed something, if only the verbiage. My 2017 O&M says 89 octane is preferred, and 87 octane is acceptable.

See my post above for HOW they adjust ignition timing to account for sensing the combustability of the gasoline octane.

Copied directly from my manual. Nothing mentioned other than 87:

FUEL REQUIREMENTS—GASOLINE
ENGINE

6.4L ENGINE

Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine. This engine is designed to meet all emissions regulations and provide satisfactory
fuel economy and performance when using high quality unleaded gasoline having a posted octane number of 87 as specified by the (R+M)/2 method.

 

[Octane]

Copied directly from my manual. Nothing mentioned other than 87:

FUEL REQUIREMENTS—GASOLINE
ENGINE

6.4L ENGINE

Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine. This engine is designed to meet all emissions regulations and provide satisfactory
fuel economy and performance when using high quality unleaded gasoline having a posted octane number of 87 as specified by the (R+M)/2 method.

More affordable with 87.My old 2013 Ram 5.7 manual states 89 preferred and 87 acceptable.The factory certainly made your 6.4 more affordable by only needing 87.I still run 89 as I grew up running 89 or higher gas and can't stop with the way my ocd works.lol

 

[Gondul]

FWIW,
2019 Manual
I ran 87 and 89 for 4 months back to back and there was no difference in logged mileage/fuel useage or 'performance'...

 

[HEMIMANN]

FWIW,
2019 Manual
I ran 87 and 89 for 4 months back to back and there was no difference in logged mileage/fuel useage or 'performance'...

View attachment 535530

Interesting, as for me there was noticeable lack of sputtering at idle and acceleration. Economy was a few tenths higher, but tow torque is what I seek in summer.
All our gas in state is mandated 10% ethanol by the corn lobby bribing politicians. Fact.

 

[Octane]

Well, no, what is better is correct octane for the ignition timing and compression ratio. Too low and you get detonation. Too high and you get unburned deposits.

This is the whole point of the octane discussion. For those of us with Hemi engines that have 89 octane preferred, it's a dilemma because there is no such thing as pure 89 octane.

Or pure 87 or pure higher octane then.So use 89 and be done.A happy median.

 

[Riccochet]

Yeah, my 2020 manual states to use 89, but that 87 is acceptable with reduced performance.

I've always ran 89.

 

[Drummin4jc]

I read through my 2024 manual and couldn’t find anything about octane recommendation. Unless I somehow skipped over it…

Adam

 

[Octane]

I can buy premium at Costco cheaper than 89 is sold here for.They dont offer 89 at Costco.So I buy premium there,and mix 87 here if needed,and save money, and still end up with 89 gas overall.

 

[HEMIMANN]

I can buy premium at Costco cheaper than 89 is sold here for.They dont offer 89 at Costco.So I buy premium there,and mix 87 here if needed,and save money, and still end up with 89 gas overall.

Exactly what I would do - if they hadn't located our local Costco at the corner of a massive intersection around 3 unsequenced stoplights and jammed with people all day, every day.

 

[Octane]

The Athens Ga Costco works out pretty well.The Duluth Ga Costco is a trainwreck of customers,parking.I won't go there at all.

 

[HEMIMANN]

The Athens Ga Costco works out pretty well.The Duluth Ga Costco is a trainwreck of customers,parking.I won't go there at all.

I would have thought corporate would have some kind of common store standards, but the stores around the Twin Cities, MN region are totally different. Of course, our area got the one that sucks the most. It's damn near inaccessible.

How do I know? I got a membership just to get the excellent hearing aid deal they have. Itty bitty perpendicular parking spaces for bug-mobiles, jam-packed, a single store entrance - at an angle! It's friggin horrendous.

 

[Drummin4jc]

My local Sam’s Club has 87 or 91 octane, no 89. I might have to do this as the Sam’s Club is in WV and I live in PA. 87 octane in PA is currently $3.49/gallon. In WV, it’s $2.99/gallon but at the Sam’s Club in WV, it’s $2.55/gallon. Crazy price difference!

Adam

 

[Octane]

I would have thought corporate would have some kind of common store standards, but the stores around the Twin Cities, MN region are totally different. Of course, our area got the one that sucks the most. It's damn near inaccessible.

How do I know? I got a membership just to get the excellent hearing aid deal they have. Itty bitty perpendicular parking spaces for bug-mobiles, jam-packed, a single store entrance - at an angle! It's friggin horrendous.

In that Duluth Ga location the convenience store owners around town, shop there in droves for their stores.And also Sams Club.Jam packed lines,then wait to get checked at the exit.My gawd!