Question about fuel octane level.

[HEMIMANN]

Adding benzene or ethanol to gasoline to increase the octane rating also reduces the amount of chemical energy. While achieving higher octane, you will also need more fuel to do the same amount of work.

The better method of increasing the octane is during the refining process, cracking and reforming hydrocarbons. As I understand it, and it has been a while, the crude quality determines the distillation methods. Which refiners produce what formulations of gasoline is a wonder.

This is where I was going. There are different levels of alkylation of the hydrocarbons that create the resistance to detonation. It's not dumping additives in, with the exception of alcohols.

I'm not going to argue anymore about it. I said what I said, from what I know about the different molecular construction. That is all.

 

[Guyfromthenorth]

Not sure if many people have done the math on Reg vs. Mid grade costs, I won't pick a side on this one as it's a personal choice but...

In my case over the 6yrs I've owned my truck I've only ever used Reg grade (including on every Ram I've previously owned, and on every fleet ram I use at work for the last 21yr). Never had knock throw a rod on me or destroy an engine.

I did some math just to see what I've saved in my 2019 alone, I err'd on the side of "better" mileage so the numbers didn't skew too heavily as I do almost entirely highway miles, so if you drive alot of city miles your savings would be quite a bit more.

With my calculations at an average of 20mpg:
Regular Gas saved me $2,016 over the last 6y of miles on my current truck vs. running Mid grade. That will keep adding up and I have no plans to move to mid-grade anytime soon.

 

[Docwagon1776]

This is where I was going. There are different levels of alkylation of the hydrocarbons that create the resistance to detonation. It's not dumping additives in, with the exception of alcohols.

I'm not going to argue anymore about it. I said what I said, from what I know about the different molecular construction. That is all.

It's more than just alcohols, benzene and the other aromatics as well. The underlying base is cracked/refined to a certain octane and additives modify it, like gasoline destined for an ethanol blend is refined to a lower octane because the minimum ethanol content will increase it.

Regardless, we can logic through this with zero understanding of the underlying chemistry.

We know that a blend isn't creating two distinct detonations with a blend where the "87 molecules" detonate before the "93 molecules" and being sold as 89 octane:

1) We reasonably know that refineries and distributors are not engaged in undetected international fraud for decades without being detected.
2) We reasonably know that gasoline is tested for octane by using it in a test engine vs a known control fuel and octane is based on when knock becomes detectable. Not an average of when the whole charge is burned, simply the presence of pre-detonation causing knock.
3) We reasonably know that if pre-detonation were occurring in the conditions set for 87 octane, it would not pass the testing for 89 octane.
4) So if "87 octane molecules" were detonating ahead of the 93, you'd detect knock, and it would not be rated as 89 octane without fraud occurring.
5) Anything sold as 89 octane (or 93 or whatever) will have the characteristics, at a minimum, of the test fuel. It may exceed it, 89 octane could test as 90 octane and it's legal and fine (and used to be more the norm, exactly because it's fraud to overrepresent but not underrepresent...the baker's dozen of gasoline). Doesn't matter how you get there, it's going to burn as an 89 octane gasoline and not have some portion of it creating knock like an 87.

 

[Wild one]

Not sure if many people have done the math on Reg vs. Mid grade costs, I won't pick a side on this one as it's a personal choice but...

In my case over the 6yrs I've owned my truck I've only ever used Reg grade (including on every Ram I've previously owned, and on every fleet ram I use at work for the last 21yr). Never had knock throw a rod on me or destroy an engine.

I did some math just to see what I've saved in my 2019 alone, I err'd on the side of "better" mileage so the numbers didn't skew too heavily as I do almost entirely highway miles, so if you drive alot of city miles your savings would be quite a bit more.

With my calculations at an average of 20mpg:
Regular Gas saved me $2,016 over the last 6y of miles on my current truck vs. running Mid grade. That will keep adding up and I have no plans to move to mid-grade anytime soon.

A lot of guys notice a milege increase with a higher octane fuel,which your calculations don't take into account.

 

[danielmid]

That was me

So long story short, our trucks will pull timing on any octane other than 91+. You just can't always hear it.

All of these examples were driving normally and unloaded in the summer. These are also on the stock tune.

On 87, my truck would pull timing almost every time I touched the gas pedal. You could actually hear it detonate audibly which I'm assuming is why they say it's "acceptable" in the owners manual.

89 is better, I never heard it audibly detonate while running it. But the pcm was still pulling timing which suggests its still detonating, just not as bad.

Which brings me to why I always run 93 in my truck. On 93 it rarely pulls timing. Only time I see it pull timing is when im pulling my camper up a long grade.

Since I dont drive the truck daily anymore, the added cost of 93 is 100% worth it for me. However I totally understand why people would want to run 89 if its daily driven.

However I would recommend staying away from 87 unless its the only option.

Is your 93 ethanol free? My truck is tuned for 91, and I have station options close of 91 E0 or 93 E10. Since, like yours, mine has been relegated to towing and not daily, I've been using the 91E0 so I'm not as worried about it sitting, but then filling up with 93E10 as we head out of town.

 

[Hemi395]

Is your 93 ethanol free? My truck is tuned for 91, and I have station options close of 91 E0 or 93 E10. Since, like yours, mine has been relegated to towing and not daily, I've been using the 91E0 so I'm not as worried about it sitting, but then filling up with 93E10 as we head out of town.

I wish it was ethanol free, I can't even get pure gas where I live...

 

[huntergreen]

It needs it because of the high compression.

Use it.

You paid good money for that truck. Do you want to risk damage to save a few $

What damage are you referring to ?

 

[Guyfromthenorth]

A lot of guys notice a milege increase with a higher octane fuel,which your calculations don't take into account.

You are correct that it could increase mileage by being able to hold a timing advance longer\more consistently. However it would need to increase mileage quite a bit, at all times, to make up a ~2000$ difference. A quick google search for peoples "impressions" of increased mileage running mid-grade shows about a 3mpg difference reported "over long trips" (highway). I checked the math and you'd need the entirety of the mileage to increase around 3mpg to break even or slightly win out with using mid-grade over regular gas. That 3mpg would also need to translate to every single mile done in the city as well and not just "over long trips", and although mid grade may well save fuel on the highway under loads like towing, or hard acceleration where advancing timing does help increase power\efficiency, I'm betting you wouldn't gain ~3mpg on all city miles by using mid-grade. Just my guess, no science to back that up.

Again just a thought experiment here, not trying to talk anyone else into what to spend\save money on. People can put whatever they want in their tanks as long as it meets manufacturer standards. I own a motorcycle with a 900 V-twin engine (nothing special). It is absolutely rated for regular grade gasoline but I put premium in it only. Part of that is because I'd rather avoid any chance of knock at WOT in a V-twin because they already vibrate around enough as is and I'd rather know that unsettling feeling is just the characteristics of that engine than wondering if I'm pinging like mad while passing another car. I also use premium grade in it because here they do not contain ethanol and as the bike isn't able to be driven for 7 months of the year where I live I want to avoid varnish in my fuel system. To each their own

 

[Wild one]

You are correct that it could increase mileage by being able to hold a timing advance longer\more consistently. However it would need to increase mileage quite a bit, at all times, to make up a ~2000$ difference. A quick google search for peoples "impressions" of increased mileage running mid-grade shows about a 3mpg difference reported "over long trips" (highway). I checked the math and you'd need the entirety of the mileage to increase around 3mpg to break even or slightly win out with using mid-grade over regular gas. That 3mpg would also need to translate to every single mile done in the city as well and not just "over long trips", and although mid grade may well save fuel on the highway under loads like towing, or hard acceleration where advancing timing does help increase power\efficiency, I'm betting you wouldn't gain ~3mpg on all city miles by using mid-grade. Just my guess, no science to back that up.

Again just a thought experiment here, not trying to talk anyone else into what to spend\save money on. People can put whatever they want in their tanks as long as it meets manufacturer standards. I own a motorcycle with a 900 V-twin engine (nothing special). It is absolutely rated for regular grade gasoline but I put premium in it only. Part of that is because I'd rather avoid any chance of knock at WOT in a V-twin because they already vibrate around enough as is and I'd rather know that unsettling feeling is just the characteristics of that engine than wondering if I'm pinging like mad while passing another car. I also use premium grade in it because here they do not contain ethanol and as the bike isn't able to be driven for 7 months of the year where I live I want to avoid varnish in my fuel system. To each their own

That milege increase skewers your math by a fair bit though,and your savings won't be as much as you claim
Are you sure about that non ethanol premium in Canada,as ethanol is mandated in Canada.I for one would like to know where you're getting ethanol free premiun at a pump in Canada,as it hasn't been available for a couple years now out here in Alberta

No, you generally cannot buy gasoline without ethanol at gas stations in Canada. Federal and provincial regulations require gasoline to contain a certain percentage of ethanol, typically up to 10%. While some premium gasolines may have lower ethanol content, completely ethanol-free gas is not typically available.

Here's why and what options you might have:

• Regulations:
  Canada mandates that gasoline sold at retail stations contains a certain percentage of ethanol.
  
  
• Exceptions:
  There are some exceptions for aviation, research, and racing, but not for regular road vehicles.
  
  
• Premium Options:
  Some premium gasolines, like Shell V-Power, may have lower ethanol content (up to 5%), but not zero, according to Shell Global.
  
  
• Ethanol Content Varies:
  The amount of ethanol can vary between gasoline grades, with lower octane fuels typically having higher ethanol content.

https://www.reddit.com/r/Chainsaw/comments/1bdc2fm/no_more_ethanol_free_gas_in_canada/

 

[KingJ2]

It's more than just alcohols, benzene and the other aromatics as well. The underlying base is cracked/refined to a certain octane and additives modify it, like gasoline destined for an ethanol blend is refined to a lower octane because the minimum ethanol content will increase it.

Regardless, we can logic through this with zero understanding of the underlying chemistry.

We know that a blend isn't creating two distinct detonations with a blend where the "87 molecules" detonate before the "93 molecules" and being sold as 89 octane:

1) We reasonably know that refineries and distributors are not engaged in undetected international fraud for decades without being detected.
2) We reasonably know that gasoline is tested for octane by using it in a test engine vs a known control fuel and octane is based on when knock becomes detectable. Not an average of when the whole charge is burned, simply the presence of pre-detonation causing knock.
3) We reasonably know that if pre-detonation were occurring in the conditions set for 87 octane, it would not pass the testing for 89 octane.
4) So if "87 octane molecules" were detonating ahead of the 93, you'd detect knock, and it would not be rated as 89 octane without fraud occurring.
5) Anything sold as 89 octane (or 93 or whatever) will have the characteristics, at a minimum, of the test fuel. It may exceed it, 89 octane could test as 90 octane and it's legal and fine (and used to be more the norm, exactly because it's fraud to overrepresent but not underrepresent...the baker's dozen of gasoline). Doesn't matter how you get there, it's going to burn as an 89 octane gasoline and not have some portion of it creating knock like an 87.

Gasoline is a solution: (Solvent + solutes)

Octane rating in gasoline is based on the concentration of iso-octane (trimethylpentane) and n-heptane. All available choices (87, 89,91, and 93) are simply different in their iso-octane/heptane ratio. There are no "87 octane molecules" or "93 octane molecules".

When you mix 87 octane and 91 octane gasoline, you mix two homogeneous (one-phase) solutions with the same solvent and solutes.

You referred, in an earlier post, to mixing two sugar aqueous solutions of different concentrations and obtaining a perfect mixture (final concentration) Cf = (C1V1 + C2V2) / (V1 + V2).

There are situations, such as mixing two heterogeneous solutions (two or more phases), where you will not get a proportional final concentration, e.g., mixing two water and oil solutions. Even if both have the same solvent (water) and solute (oil), they will not mix properly. The density of oil is lower than that of water, so that oil will remain on top, and so the final solution will not be a proper homogeneous concentration.

 

[HEMIMANN]

Gasoline is a solution: (Solvent + solutes)

Octane rating in gasoline is based on the concentration of iso-octane (trimethylpentane) and n-heptane. All available choices (87, 89,91, and 93) are simply different in their iso-octane/heptane ratio. There are no "87 octane molecules" or "93 octane molecules".

When you mix 87 octane and 91 octane gasoline, you mix two homogeneous (one-phase) solutions with the same solvent and solutes.

You referred, in an earlier post, to mixing two sugar aqueous solutions of different concentrations and obtaining a perfect mixture (final concentration) Cf = (C1V1 + C2V2) / (V1 + V2).

There are situations, such as mixing two heterogeneous solutions (two or more phases), where you will not get a proportional final concentration, e.g., mixing two water and oil solutions. Even if both have the same solvent (water) and solute (oil), they will not mix properly. The density of oil is lower than that of water, so that oil will remain on top, and so the final solution will not be a proper homogeneous concentration.

"
2. Octane Boosting Processes:

• • Catalytic Reforming:
    This process converts low-octane hydrocarbons into higher-octane ones, particularly aromatics like benzene, toluene, and xylene (BTEX).
    
  • Catalytic Cracking:
    This process breaks down larger, less desirable hydrocarbon molecules into smaller, higher-octane molecules, often resulting in gasoline with moderate octane and high olefin content.
    
  • Alkylation:
    This process combines smaller hydrocarbon molecules, like isobutane and olefins, to create branched-chain hydrocarbons with higher octane numbers.
    
  • Isomerization:
    This process converts straight-chain hydrocarbons into branched-chain hydrocarbons (isomers), which have higher octane ratings. "
    
    

 

[Docwagon1776]

Gasoline is a solution: (Solvent + solutes)

Octane rating in gasoline is based on the concentration of iso-octane (trimethylpentane) and n-heptane. All available choices (87, 89,91, and 93) are simply different in their iso-octane/heptane ratio. There are no "87 octane molecules" or "93 octane molecules".

When you mix 87 octane and 91 octane gasoline, you mix two homogeneous (one-phase) solutions with the same solvent and solutes.

You referred, in an earlier post, to mixing two sugar aqueous solutions of different concentrations and obtaining a perfect mixture (final concentration) Cf = (C1V1 + C2V2) / (V1 + V2).

There are situations, such as mixing two heterogeneous solutions (two or more phases), where you will not get a proportional final concentration, e.g., mixing two water and oil solutions. Even if both have the same solvent (water) and solute (oil), they will not mix properly. The density of oil is lower than that of water, so that oil will remain on top, and so the final solution will not be a proper homogeneous concentration.

See guys? THIS is how you nerd.

You obviously understand the underlying chemistry better than me, and the take away is the same. There are no "87 octane molecules" and once the gas is mixed it's 89 octane regardless of if it was initially refined that way or mixed at the pumping station.

 

[KingJ2]

"
2. Octane Boosting Processes:

• • Catalytic Reforming:
    This process converts low-octane hydrocarbons into higher-octane ones, particularly aromatics like benzene, toluene, and xylene (BTEX).
  • Catalytic Cracking:
    This process breaks down larger, less desirable hydrocarbon molecules into smaller, higher-octane molecules, often resulting in gasoline with moderate octane and high olefin content.
  • Alkylation:
    This process combines smaller hydrocarbon molecules, like isobutane and olefins, to create branched-chain hydrocarbons with higher octane numbers.
  • Isomerization:
    This process converts straight-chain hydrocarbons into branched-chain hydrocarbons (isomers), which have higher octane ratings. "

Thank you for the definition!

But what is your argument?

• Alkylation:
  This process combines smaller hydrocarbon molecules, like isobutane and olefins, to create branched-chain hydrocarbons with higher octane numbers.

This is how you get heptane and iso-octane in your gasoline, at the refinery:

heptane: isobutane (C4) + propylene (C3) = iso-heptane (C7) and n-heptane
isooptane: isobutane (C4)+ butylene (C4) = iso-octane (C8)

 

[Fishdoc]

I was reading through the owners manual and noticed this Ram calls for 89 octane instead of the usual 87 on past year Rams. Why the difference and is it worth it? Thanks everyone.

 

[Jackhammer Jim]

When you go to the pump and hit 89 octane, you are getting a mix of 87 octane and whatever premium they have (91 or 93 octane). Most gas stations use a mixing valve to achieve this. The 87 octane and 93 octane are mixed right there at the hose, and is sold as 89 octane because that is what it is. No one is trucking in 89 octane on a seperate truck unless is makes financial sense to do so, and so the vast majority of gas stations mix the two grades at the pump.

I run 87 octane most of the year, but run a costco mix of 87 and 93 about half and half to come out aorund 90 ish octane in the summer when towing the 6,000lb boat around. Ive towed with 87 octane and its been fine.

 

[melvingeraldmesse]

I have had really good results with the 88 octane e15 in my 2021 PW

 

[Dusty]

I'm not sure any of the mechanicals matter. Modern vehicles have much more sophisticated control of timing. Most can kick timing back far enough to safety operate with octane below the manufacturers minimum.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 134959 miles.

 

[airrecon]

I used 87 octane for the first few months then switched to 85. Cannot tell any difference - power or mpg. Up here (6000+ ft. elevation), regular is 85 octane, mid-grade is 87 octane, but premium is still 91 octane.

You are nuts. Nowhere in your manual does it state that you can use lower octane at higher altitudes. Since the days of electronic ignition, altitude does not matter! Many stations in my state of NM use 66 for regular and 88 for
midgrade. No delta in price with the few stations that use 87 and 89. Amazing how many people pay the same for a lesser product, also like you, thinking altitude matters. And make sure you use Top Tier.
You paid too much for a truck to try to save a few dollars.
By the way, I have won many bets with people claiming altitude matters.

 

[airrecon]

I'm not sure any of the mechanicals matter. Modern vehicles have much more sophisticated control of timing. Most can kick timing back far enough to safety operate with octane below the manufacturers minimum.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 134959 miles.

The problem is that you cannot tell if the knock sensor can retard the timing enough to prevent preignition. The only way to tell is sound, and you would not hear it over the engine noise.

 

[turkeybird56]

You are correct that it could increase mileage by being able to hold a timing advance longer\more consistently. However it would need to increase mileage quite a bit, at all times, to make up a ~2000$ difference. A quick google search for peoples "impressions" of increased mileage running mid-grade shows about a 3mpg difference reported "over long trips" (highway). I checked the math and you'd need the entirety of the mileage to increase around 3mpg to break even or slightly win out with using mid-grade over regular gas. That 3mpg would also need to translate to every single mile done in the city as well and not just "over long trips", and although mid grade may well save fuel on the highway under loads like towing, or hard acceleration where advancing timing does help increase power\efficiency, I'm betting you wouldn't gain ~3mpg on all city miles by using mid-grade. Just my guess, no science to back that up.

Again just a thought experiment here, not trying to talk anyone else into what to spend\save money on. People can put whatever they want in their tanks as long as it meets manufacturer standards. I own a motorcycle with a 900 V-twin engine (nothing special). It is absolutely rated for regular grade gasoline but I put premium in it only. Part of that is because I'd rather avoid any chance of knock at WOT in a V-twin because they already vibrate around enough as is and I'd rather know that unsettling feeling is just the characteristics of that engine than wondering if I'm pinging like mad while passing another car. I also use premium grade in it because here they do not contain ethanol and as the bike isn't able to be driven for 7 months of the year where I live I want to avoid varnish in my fuel system. To each their own

I had to run premium in my 2008 Ultra Classic 96cc v-twin wat it was tuned for at factory. My 2006 Honda Wing with 1832 boxer 6 allegedly reg 87 but runs a lot better on 89 especially with the heat here. I run 89 in my truck, always have. If U buy Hemi for mpg might not be the best if u think that 6000 lb truck is a Prius, lol, but I can get 20-21 on hwy with cruise 70 mph or less. Go over 70 mph well U know. I stick with 89 for all cause all my Stihl small engine motors require 89 also as does my riding mower. So just easier to also do 89 for all.

When towing with RAM run 93 specifically due to heat and load.

Peeps with 2025 rides u will find it is recommended to run 91/93 in yer 6 cylinders when towing and or hot location. Actually in the manual for 2025.

All above IMHO only.

PPLS run wateva U wanting yer rides. Your truck, your wallet.