Octane

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HEMIMANN

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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.
Exactly - and the differing Reid Vapor Pressure requirements by the Federal Government for summer & winter (higher in winter, lower in summer). Higher RVP formulation has less energy density and higher evaporation, hence higher fuel consumption for the same loads (and for colder winter ambient temperatures), and it's cheaper to produce being a higher fraction cut of crude from the distillation tower.

The reason EPA regulates summer gas to lower RVP is to reduce emissions of VOC (Volatile Organic Compounds) into the atmosphere from refueling.
 

Hauling Pillows

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It makes you wonder why did FCA design HEMI for 89 octane (preferred)?
If you ask most consumers I believe most would want a pickup truck to run on regular 87 octane and some would want 91 octane fuel for 'higher performance'. Resulting in either cheap fill-ups with 87 OR high performance with 91. Right now 89 is the worst choice (just as) expensive as 91 and not much higher performance than 87. It almost looks like some beancounter in the advertising department decide to go with 89 just so that HEMI could get closer to magical 400hp mark and make it look good on the paper. It would be just as fun with 370hp running on 87 octane. Also I find it sneaky that they do not make it obvious that 89 is preferred nor do they have a sticker inside gas door. If you haven't read manual (which most owners never read) you would not know.
I've been running 89 in my 5.7 just because I'm planning on keeping the truck for at least 100 years so I don't want to take any chances. I rather pay $15 at the pump than rebuild engine down the road. I'm not buying a story when guys say I've using 87 with no trouble for 20-30-50-100k whatever miles. That doesn't mean anything, its not going to blow up that quick and when it does its out of warranty so FCA is off the hook at that point. Between vibrations caused by MDS and possible pre-ignitions with 87 octane it makes you wonder if all these exhaust manifold bolt failures are result of it. Don't forget, there's 90lbs of weights welded to the frame to soak up all those harmonic vibrations...
I wish FCA went in a little more detail on why they made 89 preferred, it would help us understand their logic and we could use/maintain their product better without need to go on forum and discuss something as basic and ridiculous as octane content of the fuel
 

HEMIMANN

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Chrysler, or Daimler-Chrysler at the time Hemi Gen III was developed didn't create it for the average cheapskate car buyer. It was a revival of Hemi for those who remembered it, and to hook a new generation of buyers on it.

We aren't quite as sensitive to gas price (octane rating) as the average cheapskate, either. Octane requirement is a cost / benefit tradeoff in engine design. Engines designed for high octane fuel can advance spark ignition timing to get a longer pressure burn on the piston, resulting in more power and torque. The engine has to be built to take the higher peak cylinder pressure, and usually has a higher compression ratio.

OEMs are now making small, high octane engines (like wife's Mazda 2.5L I4 turbo) to maximum power output from the smallest displacement = highest fuel economy per given vehicle size. Chrysler settled on naturally-aspirated Hemi @ 89 octane for standard engine, and Hellcat supercharged for high performance. I always run mine on 89 octane top tier gas for maximized fuel economy and towing torque.
 

Tizzy

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In our area, 87 is 10%E and 89 is 15%E but cheaper per gallon. I’ve never used the 89 because of the higher % of ethanol. Should I?
 

392DevilDog

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In our area, 87 is 10%E and 89 is 15%E but cheaper per gallon. I’ve never used the 89 because of the higher % of ethanol. Should I?
Not sure what your area is...but do you mean E15 88 Octane?

I have been using the 88 for about 2 years now.

I find with my HeftyDuty it performs identical to 89 and is about 60 to 75 cents cheaper depending where I get it.

Manual states Minimum of 87 Octane and maximum of 15 % ethanol.

I will keep using it as long as the price savings is there.
 

HEMIMANN

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In our area, 87 is 10%E and 89 is 15%E but cheaper per gallon. I’ve never used the 89 because of the higher % of ethanol. Should I?

I won't use that boosted alcohol crap. Kwik Trip stations are promoting it here due to ag processor lobby bribes. Lower energy, harsher on fuel system (higher solvency), you aren't saving money. You're just refilling more often. Takes a lot of fossil fuel energy to grow corn, heat it up and distill it into alcohol. It's just a corporate welfare scam. Yeah, yeah - the oil companies get corporate welfare tax money too. But their stuff isn't bad for engines, at least.

Then you say, well top fuel NHRA race engines use nitro methanol! Yeah, and their lifespan is all of 35 seconds, too. Have at it if you wanna pay $70k for a truck and have it last half a minute.
 

SniperDroid

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We had a Flex Fuel Explorer years back.... Tried running it on E85 for about three months. On regular gas we got 15 mpg, but on E85 I got a whopping 12 mpg. The E85 was a whole ten percent cheaper. Didn't make much sense, but I had all kinds of people on a Forum tell me it was the wave of the future, and that I must be doing something wrong. Don't let me be of any influence, just do some research. Start a different thread if your truck starts to tick a little.
 

392DevilDog

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We had a Flex Fuel Explorer years back.... Tried running it on E85 for about three months. On regular gas we got 15 mpg, but on E85 I got a whopping 12 mpg. The E85 was a whole ten percent cheaper. Didn't make much sense, but I had all kinds of people on a Forum tell me it was the wave of the future, and that I must be doing something wrong. Don't let me be of any influence, just do some research. Start a different thread if your truck starts to tick a little.
Not sure who you intended this for...but just want to make it clear we were not talking about E85

This seems to be a common misconception when people mentioned E15 88 octane
 

Dean2

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Not sure who you intended this for...but just want to make it clear we were not talking about E85

This seems to be a common misconception when people mentioned E15 88 octane
No matter how you slice it, the more ethanol there is in the gas the worse the gas mileage you get. Most of our 91 and 93 premium is ethanol free. It gets way better gas mileage than the couple of 91 Octane fuels with 10% ethanol. It is well worth the effort to find a Shell, Esso or Costco and avoid Husky and Petro Canada. Given I can buy no ethanal 91 Octane at Costco for 1.24 (regular is 1.14 with 10% ethanol), and regular 87 with ethanol most other places is 1.26 makes sense to fill at Costco. Like I have said elsewhere only place I see the difference is highway, at altitude or towing. For around town, the 87 gets the same mileage.

pBP84Af.jpg

Petro Canada Ethanol for all.

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392DevilDog

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No matter how you slice it, the more ethanol there is in the gas the worse the gas mileage you get. Most of our 91 and 93 premium is ethanol free. It gets way better gas mileage than the coue of 91 Octane fuels with 10% ethanol. It is well worth the effort to find a Shell, Esso or Costco and avoid Husky and Pert can.

My fuel mileage on my RAM HeftyDuty fluctuates more with the constraint at my right ankle than any type of gas I buy.

I already explained my use of 88 in this thread.

I will continue to use it and have been very happy with the results. I have also been using it in my Jeep.

I tried using 90 non ethanol when I first got the 6.4l Hemi and there was no difference... Except the extra cost

I do run non ethanol in my mowers and dirt bike. And top up with it in my 99...only because it sits more than it gets used now.
 

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Not sure who you intended this for...but just want to make it clear we were not talking about E85

This seems to be a common misconception when people mentioned E15 88 octane
Really just a comment on what I believe is the failure of alcohol added fuels... I wish I could find pure gasoline to run in my RAM.
 

mcarey

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Damn, here in UT, I run 85 in my PW and I've had no issues.

Always assumed the 87 recommended in the manual was "regular", which is 85 for us (a minority for most of the US).
 

TigreST

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Just dropping this here (video link) seeing as how I stumbled on it on Tuesday morning. I wonder what you all will think. I tend to "not" spend money on octane that i don't need. What do you all think.



Cheers.


Tony
 
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OP
Hd74ica

Hd74ica

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Just dropping this here (video link) seeing as how I stumbled on it on Tuesday morning. I wonder what you all will think. I tend to "not" spend money on octane that i don't need. What do you all think.



Cheers.


Tony
Excellent post and video. I use 87 in my 2021 6.4 because my owner's manual says to. Truck seems to run fine. Thanks for sharing.

David
Michigan's Thumb
 

TigreST

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Glad you liked the vid. I spent 38 years in the oil refining business (process operator) the last 23 years making gasoline, diesel, jet fuel. On my motorcycle sites oil and octane are always points of contention with heated debates. My 1998 Honda Super Blackbird only every needed 86-87 (pump octane) octane. Fellow riders of the type would insist that "my machine is worthy of 91 (or better) octane" with all the added benefit of same. Not worth trying to convince them other wise of course but it do make for lively conversations.
 

FlyingRAM

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It makes you wonder why did FCA design HEMI for 89 octane (preferred)?
If you ask most consumers I believe most would want a pickup truck to run on regular 87 octane and some would want 91 octane fuel for 'higher performance'. Resulting in either cheap fill-ups with 87 OR high performance with 91. Right now 89 is the worst choice (just as) expensive as 91 and not much higher performance than 87. It almost looks like some beancounter in the advertising department decide to go with 89 just so that HEMI could get closer to magical 400hp mark and make it look good on the paper. It would be just as fun with 370hp running on 87 octane. Also I find it sneaky that they do not make it obvious that 89 is preferred nor do they have a sticker inside gas door. If you haven't read manual (which most owners never read) you would not know.
I've been running 89 in my 5.7 just because I'm planning on keeping the truck for at least 100 years so I don't want to take any chances. I rather pay $15 at the pump than rebuild engine down the road. I'm not buying a story when guys say I've using 87 with no trouble for 20-30-50-100k whatever miles. That doesn't mean anything, its not going to blow up that quick and when it does its out of warranty so FCA is off the hook at that point. Between vibrations caused by MDS and possible pre-ignitions with 87 octane it makes you wonder if all these exhaust manifold bolt failures are result of it. Don't forget, there's 90lbs of weights welded to the frame to soak up all those harmonic vibrations...
I wish FCA went in a little more detail on why they made 89 preferred, it would help us understand their logic and we could use/maintain their product better without need to go on forum and discuss something as basic and ridiculous as octane content of the fuel
The reason for 89 octane is engine ignition timing and “detonation”. Higher performance engines with advanced timing require higher octane, which simply resists detonation or “knocking” which is harmful to engines. To get the Hemi performance, you pay for higher performance fuel. The Hemi could be tuned to run on 87 octane, but performance would be lost along with smiles. Advanced timing gains more performance but requires higher octane to resist harmful detonation.

Avweb.com has an informative video on aviation gasoline which is Leaded 100 octane (check YT). The reason many aircraft engines require 100 octane is advanced engine timing, usually around 28-32 degrees before TDC (top dead center). In order to ring out the most power to weight ratio the timing is advanced aggressively which requires a high octane fuel to resist detonation.

My 4.7 liter (not a Hemi) runs in 87 due to it being a lower performance engine, and it can also run on flex fuel E85. Surprisingly it runs better on E85 flex fuel as I’m guessing the engine can take advantage of the higher octane (105 posted on the pump).
 

Curmudgeon

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Just dropping this here (video link) seeing as how I stumbled on it on Tuesday morning. I wonder what you all will think. I tend to "not" spend money on octane that i don't need. What do you all think.



Cheers.


Tony

I agree with avoiding spending spending money on anything that doesn't matter. The video was interesting and, I think, the tests were well done to my eye.

I can't recall, even going back to the '70s, where my "butt-dyno" could tell 87 from 93, or even 95. As i said earlier I'm just trying to find the "best" gas I can.
My 5.7L is the largest and most powerful engine I've ever owned and I've been very happy with it's performance. I've never made any performance mods to any vehicle, probably never will.

I'm far more concerned with quality, consistency. Clean gas. Quality gas. Detergent gas. Top Tier gas.
I won't allow performance to suffer because that would likely be bad for the engine/vehicle.

So, I guess my questions is this: is there anything about 93 that makes it better than 91, or 89, or 87? I've been using mid-grade for decades simply because I didn't like the idea of putting the cheapest I could find into a vehicle that is a form of investment for me.
 

Tulecreeper

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The reason for 89 octane is engine ignition timing and “detonation”. Higher performance engines with advanced timing require higher octane, which simply resists detonation or “knocking” which is harmful to engines. To get the Hemi performance, you pay for higher performance fuel. The Hemi could be tuned to run on 87 octane, but performance would be lost along with smiles. Advanced timing gains more performance but requires higher octane to resist harmful detonation.

Avweb.com has an informative video on aviation gasoline which is Leaded 100 octane (check YT). The reason many aircraft engines require 100 octane is advanced engine timing, usually around 28-32 degrees before TDC (top dead center). In order to ring out the most power to weight ratio the timing is advanced aggressively which requires a high octane fuel to resist detonation.

My 4.7 liter (not a Hemi) runs in 87 due to it being a lower performance engine, and it can also run on flex fuel E85. Surprisingly it runs better on E85 flex fuel as I’m guessing the engine can take advantage of the higher octane (105 posted on the pump).
Mine is. Says right in my book, "Use 87 Octane with no more than 15% ethanol".
 

Octane

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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
 
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