Octane

Nyca · Oct 5, 2021

I guess somebody already said that.
The higher octane prevents knock in the combustion chamber.
I’m running 93 octane, but I’m tuned for that as well.
I’m not saying that 87 octane would cause knock, but the higher the octane the less chance for knock.

Just my two cents.

RacerRon · Oct 5, 2021

Keep in mind that for pre-ignition to happen, fuel has to be present in the combustion chamber as the gasses are compressed. These are direct injected engines. The fire only happens when the fuel is actually injected almost like a diesel. My 2021 6.4 manual only states 87. I have run a couple of tanks of 91 and saw no measurable difference in economy or power. Only a slightly lighter wallet.

Smokey613 · Oct 6, 2021

We run 87 except when towing our TT then we run 89.

HEMIMANN · Oct 6, 2021

Hemis are not direct injection engines. They are port fuel injected.

turkeybird56 · Oct 6, 2021

HEMIMANN said:
Hemis are not direct injection engines. They are port fuel injected.

I run 89, per the manual instead of 87. But hey, even my Stihl Chain Saw says 89 Octane. So when I go and gas up, and get gas in cans, etc, just do 89 and be done with it. But everybody is different and has different thoughts and opinions.

Hd74ica · Oct 6, 2021

What year is your

turkeybird56 said:
I run 89, per the manual instead of 87. But hey, even my Stihl Chain Saw says 89 Octane. So when I go and gas up, and get gas in cans, etc, just do 89 and be done with it. But everybody is different and has different thoughts and opinions.

What year is your truck, 6.4 or 5.7?

392DevilDog · Oct 6, 2021

turkeybird56 said:
I run 89, per the manual instead of 87. But hey, even my Stihl Chain Saw says 89 Octane. So when I go and gas up, and get gas in cans, etc, just do 89 and be done with it. But everybody is different and has different thoughts and opinions.

I only use non ethanol gas in any of my small engines, etc.

I actually just buy the pre mixed stuff in the cans...makes it easy for storing and having just what i need for the job.

When it comes to the truck...i buy what is cheapest. It does not stay in the tank long anyways.

Moose2 · Oct 6, 2021

How’s this for “octane”......

turkeybird56 · Oct 6, 2021

Hd74ica said:
What year is your

What year is your truck, 6.4 or 5.7?

2019 Bighorn CC 4 X 4, 5.7L non-etorque. No mods except for better air cleaner insert. (in my signature on posts)

Hd74ica · Oct 6, 2021

Looks like you got enough octane there to get you to an AA meeting. Bawhahaa, just kidding.

Moose2 said:
How’s this for “octane”......

hemihustlin · Oct 6, 2021

Moose2 said:
How’s this for “octane”......

Up here we have a malt alcohol and caffeine beverage sold in just about every corner store called octane I was sure I was going to see one in your photo.

https://images.app.goo.gl/4tdetnBLbh7Yzo9R9

Moose2 · Oct 6, 2021

Hd74ica said:
Looks like you got enough octane there to get you to an AA meeting. Bawhahaa, just kidding.

That 14% out to be a fun one. Those are from a house I just cleaned out. Can‘t throw perfectly good beverages out, that would be a crime!

Extra fuel for when I need to do some drinking’ thinking’.

RBJRBJ · Oct 7, 2021

While my 2021 Ram 1500 Longhorn with 5.7L Hemi with eTorque runs well on 87 octane, I switched to 89 octane and truck runs smoothly with minimal decrease in fuel consumption. Truck is driven mainly on highway and at high speeds (average 70mph).

Octane · Oct 7, 2021

RBJRBJ said:
While my 2021 Ram 1500 Longhorn with 5.7L Hemi with eTorque runs well on 87 octane, I switched to 89 octane and truck runs smoothly with minimal decrease in fuel consumption. Truck is driven mainly on highway and at high speeds (average 70mph).

This 87 thats been in use since the seventies imo has never done quite as well as 89 in any vehicle we've ever owned.87 works,but 89 changes the tune just slightly enough over several tankfuls to justify me using it also.My dealer told me my Miata even,was supposed to run premium but if it didnt rattle and knock ping on lesser grades then it was alright to run.They said it would "detune" ignition timing and performance some by using lower grades tho.

Dean2 · Oct 7, 2021

Lord love a Duck! Yes the ECM will set the tune to match the octane used, and yes it takes a few tanks to know for sure what the Octane level does. That is the true beauty of computer contoled ignition and fuel injection. That said, the long and short is, sufficiently ******** timing should reduce your mileage. It did in the old distributor and carb days, still does today. In real hot weather, the ECU will retard the timing enough to be visible in the gas mileage you get. Other conditions, like towing at altitude, will often show the same effects. However, if you get almost exactly the same mileage out of lower Octane after 4 or 5 tanks as you do out of 4 or 5 test tanks of 89, 91 or 93, then the retardation of the timing is not sufficient to affect efficiency. If you cannot show enough increased mileage to cover the increased cost then there is zero benefit to running the higher Octane. The 87 Octane will not harm your motor or FCA would not be telling you it is okay to use it.

Octane · Oct 7, 2021

Lord,love aDuck! Lol.
They call me Octane...hi octane.My timing is always correct.And my motors never been a derelect.Octane,hi Octane...that's my name.But fill me up with the incorrect and I'll never be anything but a wreck.

brilliantnick · Oct 7, 2021

Im surprised noone has linked engineering explained vid about octane

Never Use This Gas In Your Car!

How 85 Octane Fuel Can Destroy Your Engine And Void Your WarrantySubscribe to Engineering Explained for more videos! - https://goo.gl/VZstk7Recommended Books...

youtu.be

This video explains octane, what it is and its relationship to altitude (like why high altitude states have generally lower octane for 'regular.' but then goes into details about difference between old carb vehicles vs modern vehicles.

My friend in utah has a carb motorbike that he says has a manual that says 87 but most stations around there sells 85 as regular so he has to go midgrade. On the occasion he has fueled up with the 85 he had issues with knock. Not to contradict jason but the only thing he was doing listing as 'more likely' was max throttle... Which i think is the biggest influence for demands on gas.

Anyway my takeaway, 87(or whatever recommend) octane no matter elevation. If under load ie towing or hilly= mid or premium

RacerRon · Oct 7, 2021

HEMIMANN said:
Hemis are not direct injection engines. They are port fuel injected.

Oops....my bad. I was thinking DI....This makes the ability to run on 87 all that more impressive.

HEMIMANN · Oct 7, 2021

RacerRon said:
Oops....my bad. I was thinking DI....This makes the ability to run on 87 all that more impressive.

np - but the ability to run on gasoline octane levels is really predicated on how hot the combustion chamber gets prior to spark ignition - and this means compression ratio and air induction type. The higher the compression pressure and temperature, the higher the octane rating.

It is pointless to jack up the compression ratio and turbocharging if you can't specify higher octane gasoline. The entire point of doing this is to get more power from the same engine size. And then you can also advance the spark ignition timing for more power, as the cylinder pressure goes higher with the ignition starting sooner.

RacerRon · Oct 8, 2021

I have an in depth knowledge of the combustion and octane requirements. I have been building and drag racing my own stuff for over 30 years. It never ceases to amaze me how people will argue over required octane. Also, one must keep in mind that all 87 is not the same. If the fuel has a high R number but a lower M number, it may detonate in an engine that a different 87 is fine in. Higher vols of winter fuels may detonate in a high load summer application etc.

I do know that so far my truck is happy on 87.

Octane

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