Octane

[06 Dodge]

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.

The one time I bought gas at a MSP Costco (back in summer of 2018, off I-35W & CR 42) it was a cluster, don't even want to see how bad it is today, wife and I never did understand why they put the pumps where an how they did and fully understand why you would not want to buy gas at that lactation....

 

[HEMIMANN]

The one time I bought gas at a MSP Costco (back in summer of 2018, off I-35W & CR 42) it was a cluster, don't even want to see how bad it is today, wife and I never did understand why they put the pumps where an how they did and fully understand why you would not want to buy gas at that lactation....

That doesn't stop 'em up at my location. They'll wait in line for an hour at -10 below or +100 above to save $2.

 

[RamDiver]

That doesn't stop 'em up at my location. They'll wait in line for an hour at -10 below or +100 above to save $2.

And don't forget, most drivers waiting at Costco pumps are driving tiny little cars with tiny little gas tanks, that are likely getting 40 mpg or better. LOL

The lines move pretty fast at the Costco I use but as soon as the line reaches the previous cross-road into the main parking lot, that's a hard pass for me.

.

 

[BossHogg]

I burn diesel so I don't do the Costco wait for gas. At my club, lines are often backed up onto the street making it nearly impossible to access the club's parking lot (or get out). To make it worse, the club is landlocked. On average, they are $.25 per gallon less than the street price.

With the typical car having a 16-gallon tank, and assuming most are about 3/4 of a tank low, that makes their gas purchase about 12 gallons or a savings of $3 over street prices. Waiting in line, on average about 20 minutes, it isn't worth it to me.

I've noticed that Costco has noticed that their gas islands need a better design. In newer built clubs I've recently been to, (Queens Creek AZ, and Melbourne FL) the clubs are located in a light industrial parkway setting with massive fuel islands consisting of four island runways with 6 pumps and room for additional pumps. The pumps also carry diesel, unlike the existing older Costcos.

 

[Riccochet]

My time is worth more than saving a buck or two. I won't wait in line for gas.

 

[FlyingRAM]

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

So some hemis can run on 87, if it says so in the manual, it must be true. The OP referred to his Hemi requiring 89 and he was asking why it couldn’t run on 87. I don’t know all the different types of Hemis, but I was explaining why higher octane is required in some engines. A Hemi would not necessarily require higher octane, but if it were tuned from the factory or afterwards for 89 or higher octane, then running lower octane could harm the engine from detonation. Higher compression engines with advanced timing require a higher anti-knock (octane) fuel.

 

[HEMIMANN]

I watched a repeat of Engine Masters from 2021 on Motortrend TV this snowy afternoon.

They ran the same engine at the same timing to prove, of course, gasoline with differing octane ratings have no effect on engine torque or power.

They finally admitted their tests were misleading - because the engine they used had the ignition timing already set for optimum fuel burn for the compression ratio and max air volume at WOT.

So essentially, they proved nothing. They grudgingly admitted that consumer engines from the factory are now available with differing ignition timing for different octane gas. I was disappointed in their ranting for the majority of the tests.

IF - the factory optimizes the ignition timing for max power, then the octane gas needed to prevent detonation at this timing is set - no higher octane will do anything but waste money and create deposits.

So why did Daimler-Benz-Chrysler design the Gen III Hemi to need 89 octane gas? Probably to get more power from the given displacement and compression ratio, no? Then telling us their ECM algorithm allows use of 87 octane - because let's face it, the gas price difference in octane is a big deal to a lot of people that wouldn't buy the Ram Hemi if they didn't do this.

That said, we've established that it's not great for engine longevity to run on 87 octane.

Yes, I know - more ranting about established facts.

Thank you for reading my TedTalk.

 

[Tulecreeper]

I watched a repeat of Engine Masters from 2021 on Motortrend TV this snowy afternoon.

They ran the same engine at the same timing to prove, of course, gasoline with differing octane ratings have no effect on engine torque or power.

They finally admitted their tests were misleading - because the engine they used had the ignition timing already set for optimum fuel burn for the compression ratio and max air volume at WOT.

So essentially, they proved nothing. They grudgingly admitted that consumer engines from the factory are now available with differing ignition timing for different octane gas. I was disappointed in their ranting for the majority of the tests.

IF - the factory optimizes the ignition timing for max power, then the octane gas needed to prevent detonation at this timing is set - no higher octane will do anything but waste money and create deposits.

So why did Daimler-Benz-Chrysler design the Gen III Hemi to need 89 octane gas? Probably to get more power from the given displacement and compression ratio, no? Then telling us their ECM algorithm allows use of 87 octane - because let's face it, the gas price difference in octane is a big deal to a lot of people that wouldn't buy the Ram Hemi if they didn't do this.

That said, we've established that it's not great for engine longevity to run on 87 octane.

Yes, I know - more ranting about established facts.

Thank you for reading my TedTalk.

Unless, of course, your manual specifically says to use 87 without even a hint that any other octane should be used. A direct copy from my Users Manual:

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.

 

[HEMIMANN]

Unless, of course, your manual specifically says to use 87 without even a hint that any other octane should be used. A direct copy from my Users Manual:

FUEL REQUIREMENTS—GASOLINE ENGINE
6.4L Engine
Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine.
View attachment 537602
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.

What model year? I wonder if they lowered compression ratio?

This is not what my manual says.

 

[Tulecreeper]

What model year? I wonder if they lowered compression ratio?

This is not what my manual says.

It's in my signature line - 2023, 2500.

 

[KKBB]

It's in my signature line - 2023, 2500.

My 2019 6.4 says the same. 87 octane. No mention of 89 octane.

 

[Wild one]

What model year? I wonder if they lowered compression ratio?

This is not what my manual says.

The 6.4 has been the same compression ratio from when they introduced it in 2014.
I know my big 700 page manual for my 14 says only 87 for the truck 6.4,and doesn't say anything about using 89.

 

[HEMIMANN]

The 6.4 has been the same compression ratio from when they introduced it in 2014.
I know my big 700 page manual for my 14 says only 87 for the truck 6

4,and doesn't say anything about using 89.

The 6.4 has been the same compression ratio from when they introduced it in 2014.
I know my big 700 page manual for my 14 says only 87 for the truck 6.4,and doesn't say anything about using 89.

Yeah, but you're in CA, remember there are differences in fuels and such?

Anyway here is the screen print from my 2017 2500 with 6.4L Hemi. Unambiguous as I stated -

 

[Riccochet]

If engine internals remained the same throughout the years then the only thing they can be adjusting via programming is timing.

 

[Ratman6161]

Yeah, but you're in CA, remember there are differences in fuels and such?

I'm in Minnesota and the manual for my 2022 says 87 with no m3ntion of anything else.

 

[ramffml]

Yeah, but you're in CA, remember there are differences in fuels and such?

Anyway here is the screen print from my 2017 2500 with 6.4L Hemi. Unambiguous as I stated -

View attachment 537615

To be honest, the owners manual seems to be ridiculously unreliable, changing it's mind more than an angsty teen.

Between the changing octane and oil requirements from year to year, its safest to just follow common sense and put the best stuff in we can find at all times. So minimum of 89 for octane, and 5w-30 for oil.

 

[HEMIMANN]

To be honest, the owners manual seems to be ridiculously unreliable, changing it's mind more than an angsty teen.

Between the changing octane and oil requirements from year to year, its safest to just follow common sense and put the best stuff in we can find at all times. So minimum of 89 for octane, and 5w-30 for oil.

Was that you that ran the datalogger showing how the ECM did short and long term knock sensing to r*e*t*a*r*d ignition timing?

I can't believe this company is sophisticated enough to change ECM algorithms, once set. Which would mean, if true, the Owner's Manual was changed be their Sales Dept. to pander to "value sensitive" target customers that refuse to pay extra for 89 octane gas. Having been in this industry for 22 years, this smells like what they did.

From what I've learned here from members like you, I would run 89 octane min. in the 6.4, and 91 octane in the 5.7, since it has higher compression ratio.

 

[Riccochet]

Was that you that ran the datalogger showing how the ECM did short and long term knock sensing to r*e*t*a*r*d ignition timing?

I can't believe this company is sophisticated enough to change ECM algorithms, once set. Which would mean, if true, the Owner's Manual was changed be their Sales Dept. to pander to "value sensitive" target customers that refuse to pay extra for 89 octane gas. Having been in this industry for 22 years, this smells like what they did.

From what I've learned here from members like you, I would run 89 octane min. in the 6.4, and 91 octane in the 5.7, since it has higher compression ratio.

That's the most logical explanation for the switch to 87. Marketing. They probably didn't see enough warranty work come in due to people running 87. So let people run 87, who cares if it pulls a degree or two and you lose 5-10 HP. Most people would never notice that.

There's no law forcing them to be accurate with the power numbers anyways.

 

[Curmudgeon]

Was that you that ran the datalogger showing how the ECM did short and long term knock sensing to r*e*t*a*r*d ignition timing?

I can't believe this company is sophisticated enough to change ECM algorithms, once set. Which would mean, if true, the Owner's Manual was changed be their Sales Dept. to pander to "value sensitive" target customers that refuse to pay extra for 89 octane gas. Having been in this industry for 22 years, this smells like what they did.

From what I've learned here from members like you, I would run 89 octane min. in the 6.4, and 91 octane in the 5.7, since it has higher compression ratio.

I went from 89 octane to Exxon 93 octane for 1 tank, both "top tier" by pump label and the web site. MPG seemed to drop a couple tenths.
Now I'm using Sunoco 89, official butt dyno results are good, and MPG is back up a couple tenths. That said there are more important concerns for me than, say, 0.3 MPG.

As with the 6.4L has the documentation for the 5.7L seen such changes over the years? My Sunoco has a good variety of octanes and I haven't tried the 91. I'm on my 3rd fill of 89 octane from the same station.

My tank is 95% full right now so it will be a bit before I can fill with 91, but all I get from my butt dyno is that there is no difference in anything from 87 to 93 so I don't know what to look for. Maybe another 0.3 MPG variance?

 

[Dean2]

2021 2500 Owners Manual, Canadian Specification Pickup. No mention of 89 Octane. 2020 Grande Cherokee with 5.7 does talk about 89 and 87 as the option. In the 6.2 and 6.4 for the Cherokee it even talks about using 91 Octane to match the tune in that application and that 91 is REQUIRED.