For the guys who think they get more power with 91 octane fuel

ThunderMug95 · Nov 7, 2022

I run 93 in mine 90% of the time. In VA we have 87, 89, 93 at prob 75% of pumps. Some 89/91, but not a lot. When gas shot up in $ I ran a few tanks of 87. My Hemi was upset with me. Kinda like the cats when I switch them from canned food to dry. The Ram didnt **** outside the litter box like the cat, but it absolutely vocalized it’s displeasure.

HEMIMANN · Nov 7, 2022

Detonation is never good in a spark ignited engine.

It's just a matter of accumulation of knocking that determines when the piston crown will crack. I don't intend to be a field test subject for the coder bro's.

But I do know a fair amount about fracture mechanics.

Ratman6161 · Nov 7, 2022

And the correct answer is...drum roll...use the octane level specified in your owners manual. In the case of my 2022 2500 6.4, that's 87. Just for grins I've tried all the variations available le in my area including 87 E10, 88 E15, 91 E15, and 91 ethanol free (but not E85, obviously). I've done this both while unloaded and while towing my travel trailer and have not noticed any difference in power or MPG.

About the only exceptions for me were with previous vehicals or living at higher altitudes. Some examples:
1. From 2010 to 2013 I had a flex fuel Ford Escape V6. There definitely was a decrease of about 5 MPG on E85 vs 87 E10. I did the math and figured out that if E85 was at least $.70 per gallon cheaper it was worth while. It was usually more like $.30. No noticible difference in power but the engine did seem less responsive on E85.

2. When I lived in CO I used 85 which is fine at altitude. But if I was headed east towards lower altitude, I'd fill up with a higher grade just in case. Also, I had a 2001 Corvette that just didn't like the 90 octane "premium" common in there (lived in Colorado Springs, about 6000 feet) regardless of altitude.

But hey, it's your money so if you figure you know more than the engineers that designed the thing, then go for it.

Shawn Burns · Nov 7, 2022

Since our price hike of fuel, one benefit that I noticed was that the price difference loyally between 89 and 93 was $.05. I decided to try a tank full before a three hour drive Towing a 12 ft race trailer. To my delight, I achieved at least 1 mpg average better than I've ever done towing on that trip. I made the easy decision to o opt for the fuel to help protect the engine from detonation during the trip. I am used to seeing 245 degree engine oil Temps, so the added safety margin was worthwhile for my decision making process.

I come from a high performance motorcycle and turbo car background, so I am aware that running any excess octane past what is required by the design of the engine is wasteful and typically results in less power.

On a side note, I tried another test of octane free fuel while Towing. I did not notice a difference between 91 non ethanol and 93 e10 .

This is my own anecdotal experience and shouldn't be critiqued as a scientific study.

With that being said, the truck runs about the same unloaded with 91 compared to 93. I am running an edge tuner and I am able to run the hp map with 93. I attribute the mpg gain to the ability of the truck to hold 8th gear longer while Towing.

I hope this helps someone.

2020PW · Nov 7, 2022

This is just like the oil and oil filter trends. It’s all a placebo that make people feel better.

FYI, we have a fleet of vehicles and run the cheapest oil, filter and fuel we can get. No problems to date besides normal maintenance…. LMAO

Mopar440 · Nov 7, 2022

The HEMI has a 10:1 Compression Ratio. The owners manual recommends a minimum of 89 octane. The same as with my old 94 Intrepid ES with the 3.5L (10:1 & min. 89 Octane). I ran the Intrepid on 91 Octane (sometimes 93 or 94 for a treat) and got great performance and amazing fuel mileage (37mpg Hwy vs 33mpg Hwy EPA). Since day one (I bought my Ram brand new in 2017) I have run it on 91 octane and on occasion 94 octane). The engine runs clean, smooth, great performance, very responsive (the 3.92:1 gears help) and I get pretty good gas mileage both hwy and city (when driving efficiently, as has been the case lately with the fuel prices).

Can you run the engine on 87? Yes. Will you damage he engine on 87? Not likely
The engine has knock sensors. With these, the computer adjusts the ignition timing to compensate for the octane and eliminate engine knock (ping/detonation/pre-ignition) by retarding the ignition timing. When running 91 octane, the computer advances the timing to maximum efficiency/performance.

Also, most 91 fuels don't have Ethanol. 87 has up to 10%, 89 up to 5% and none in 91 and higher. However, some oil companies are starting to add up to 10% ethanol to all grades of gas (with the exception of E85 which has up to 85% ethanol).

The bottom line: My engine runs better on 91 octane, gives me better and more responsive performance and better fuel economy. While driving efficiently, it is actually cheaper for me to run 91 octane than 89 or 87 octane as the tank lasts me much longer than with the lower octane fuels. Yes, it costs more to fill up but in the long run, it's cheaper. Of course that goes right out the window when you drop the pedal to the floor and use all 395 Hp, then it is going to drink like a thirsty pig in the desert.

Wild one · Nov 7, 2022

Mopar440 said:
The HEMI has a 10:1 Compression Ratio. The owners manual recommends a minimum of 89 octane. The same as with my old 94 Intrepid ES with the 3.5L (10:1 & min. 89 Octane). I ran the Intrepid on 91 Octane (sometimes 93 or 94 for a treat) and got great performance and amazing fuel mileage (37mpg Hwy vs 33mpg Hwy EPA). Since day one (I bought my Ram brand new in 2017) I have run it on 91 octane and on occasion 94 octane). The engine runs clean, smooth, great performance, very responsive (the 3.92:1 gears help) and I get pretty good gas mileage both hwy and city (when driving efficiently, as has been the case lately with the fuel prices).

Can you run the engine on 87? Yes. Will you damage he engine on 87? Not likely
The engine has knock sensors. With these, the computer adjusts the ignition timing to compensate for the octane and eliminate engine knock (ping/detonation/pre-ignition) by retarding the ignition timing. When running 91 octane, the computer advances the timing to maximum efficiency/performance.

Also, most 91 fuels don't have Ethanol. 87 has up to 10%, 89 up to 5% and none in 91 and higher. However, some oil companies are starting to add up to 10% ethanol to all grades of gas (with the exception of E85 which has up to 85% ethanol).

The bottom line: My engine runs better on 91 octane, gives me better and more responsive performance and better fuel economy. While driving efficiently, it is actually cheaper for me to run 91 octane than 89 or 87 octane as the tank lasts me much longer than with the lower octane fuels. Yes, it costs more to fill up but in the long run, it's cheaper. Of course that goes right out the window when you drop the pedal to the floor and use all 395 Hp, then it is going to drink like a thirsty pig in the desert.

Things must be differant in Ont then out here in Alberta,as even the 93/94 out here can have up to 10% ethanol

CheechDogg.0n37s · Nov 7, 2022

Mopar440 said:
The HEMI has a 10:1 Compression Ratio. The owners manual recommends a minimum of 89 octane. The same as with my old 94 Intrepid ES with the 3.5L (10:1 & min. 89 Octane). I ran the Intrepid on 91 Octane (sometimes 93 or 94 for a treat) and got great performance and amazing fuel mileage (37mpg Hwy vs 33mpg Hwy EPA). Since day one (I bought my Ram brand new in 2017) I have run it on 91 octane and on occasion 94 octane). The engine runs clean, smooth, great performance, very responsive (the 3.92:1 gears help) and I get pretty good gas mileage both hwy and city (when driving efficiently, as has been the case lately with the fuel prices).

Can you run the engine on 87? Yes. Will you damage he engine on 87? Not likely
The engine has knock sensors. With these, the computer adjusts the ignition timing to compensate for the octane and eliminate engine knock (ping/detonation/pre-ignition) by retarding the ignition timing. When running 91 octane, the computer advances the timing to maximum efficiency/performance.

Also, most 91 fuels don't have Ethanol. 87 has up to 10%, 89 up to 5% and none in 91 and higher. However, some oil companies are starting to add up to 10% ethanol to all grades of gas (with the exception of E85 which has up to 85% ethanol).

The bottom line: My engine runs better on 91 octane, gives me better and more responsive performance and better fuel economy. While driving efficiently, it is actually cheaper for me to run 91 octane than 89 or 87 octane as the tank lasts me much longer than with the lower octane fuels. Yes, it costs more to fill up but in the long run, it's cheaper. Of course that goes right out the window when you drop the pedal to the floor and use all 395 Hp, then it is going to drink like a thirsty pig in the desert.

I ran 89 for a whole year until this past September ... my truck just didn't like 89 ... went back to 91 and my truck is loving it ... I ran nothing but 91 since the first day I brought it home and read a few threads where people said 89 was fine ... nope ...don't care what anyone says, on 89 you can feel the drop in performance, hesitation and less MPGs even though I don't care about MPGs I sure don't mind getting back those 2-3 MPG that 91 gives me ....

Docwagon1776 · Nov 7, 2022

Elkman said:
Actually more energy is used to produce ethanol than it provides in our cars and trucks...

Actually no, modern ethanol production is decidedly energy positive.

tron67j · Nov 7, 2022

My 6.4 owner manual allows both 87 and 89. I run 87 all the time unless I am towing, then run 89. Never a problem. Using a higher octane than called for is just a waste of money for me.

Brandon-w · Nov 7, 2022

I can only run 91 in my hemi

dhay13 · Nov 7, 2022

HemiMann is correct, your engine will have minor detonation before you can hear it. The problem this will usually cause is cracked/broken ring lands.
And hard to compare todays engines from engines from 30 years ago. Aluminum heads and/or blocks help dissipate heat better to allow for higher compression, as well as more efficient combustion chamber design and variable valve timing. Back in the carb days 9.5:1 was pushing the limits of pump fuel. Today I think some are pushing 10.5:1. I had 10.7:1 in my '57 Chevy and ran it on 93 octane but my camshaft had alot of overlap. Had a 393 (de-stroked 406) with aluminum AFR heads, Ross pistons, Hank the Crank crank with 6" Oliver rods. Dyno'd at 552HP at I think 6400RPM.

2020PW · Nov 7, 2022

dhay13 said:
HemiMann is correct, your engine will have minor detonation before you can hear it. The problem this will usually cause is cracked/broken ring lands.
And hard to compare todays engines from engines from 30 years ago. Aluminum heads and/or blocks help dissipate heat better to allow for higher compression, as well as more efficient combustion chamber design and variable valve timing. Back in the carb days 9.5:1 was pushing the limits of pump fuel. Today I think some are pushing 10.5:1. I had 10.7:1 in my '57 Chevy and ran it on 93 octane but my camshaft had alot of overlap. Had a 393 (de-stroked 406) with aluminum AFR heads, Ross pistons, Hank the Crank crank with 6" Oliver rods. Dyno'd at 552HP at I think 6400RPM.

If that’s the case run SS100 or GT260.

sandawilliams · Nov 7, 2022

mtofell said:
I don't notice much, if any, difference going 87 to 89 octane but man when I get the non-ethanol my truck sure does run nice. I camp each summer at a remote place that only sells non-ethanol and it's nice. Sure, I can find it at home but it's usually $1-2 more per gallon so I'll pass.

Speaking of ethanol in gas I always remember what I read on one of these forums once.... A guy who had spent his life working in the fuel business as an engineer, etc. He knew a ton about fuel, refining and distribution. His opinion was that most vehicles get 10% less MPGs with 10% ethanol and the only reason it was mandated by our govt. in our gas was to keep corn farmers in business. I'm just the messenger but don't find it hard to believe that our govt. would do something that stupid.

Ethanol- the biggest scam our government ever laid on us.

Wild one · Nov 7, 2022

Brandon-w said:
I can only run 91 in my hemi

Hey you bandit, it's good to see you again. Your truck with the 10.9:1 SRT 6.4 will require 91 :waytogo:

HEMIMANN · Nov 7, 2022

Wow...members take time to share datalogs with explanations and new guys just blow it off.

I mean, what's the point of being here beyond flouting ignorance? Sad.

CheechDogg.0n37s · Nov 7, 2022

One reason why gas especially high octane in California is so expensive and is so good against knocking is Alkylate .... California is the only State that requires all gas to have Alkylate when other states can get away with dirtier gas ....

Alkylate is another reason why 91 octane here in California is so good even for vehicles that don't need 91 ... Chevron actually has the first Alkylate refinery in Salt Lake along with Aspen from what I have been reading ... pretty interesting .....

Have you guys heard about Alkylate in high octane gas?

DILLIGAF · Nov 7, 2022

Brandon-w said:
I can only run 91 in my hemi

Im in that club

Funny thing is I still do Log files once in a while to confirm that I have no issues.

westcoasting · Nov 7, 2022

Anyone run 94 octane?

dhay13 · Nov 7, 2022

2020PW said:
If that’s the case run SS100 or GT260.

I ran CamII or Turbo Blue in my higher compression engines but 93 was fine in the 393

For the guys who think they get more power with 91 octane fuel

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