Anyone switched to 87 octane?

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HEMIMANN

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What does optimum performance mean and why would they use those words in the owners manual? You can use 87 and there likely wont ever be an issue, but it is not optimum performance. Neither is 91, but I use 91 because costco here doesnt sell 89.

And here I was doing to ask if you could tell a difference between 89 and 91.

They still sell 89 octane up here, with 10% ethanol only, state-mandated (as is 87 octane). So, I can tell it runs smoother on 89 / 10 than 87 / 10. Did not try 91 because supposedly the engine won't advance ignition timing further to take advantage of it, and without that it leaves more unburned deposits.

The moral of the story is to run the lowest octane your engine has ignition timing advance setting. Many tuners have a 91 or higher octane power setting that will advance ignition timing further. I have that too, just not interested in a race truck. I use the tow setting which still calls for 89 octane.

Another interesting tidbit in Minnesota - state law allows sale of 91 octane pure gas for sensitive engines - motorcycles, outboards, chainsaws, other 2-strokes, etc. State law prohibits using 91 octane pure gas in modern vehicles, yet there is zero enforcement. Usually there is just one or two pumps of this small engine gas at a station, but stations also sell 91 octane with 10% ethanol for high compression and/or turbocharged engines like wifey's Mazda that prefers it.

Finally, the ethanol mafia in Minnesota bribed the legislature to promote 88 octane with 15% ethanol gas, along with E85 which is 85% ethanol for 'flex fuel' engines. This is all just agri-processor giant bribery of government. Food grown for fuel. The culprits here are Cenex (CHS now), Archer-Daniels-Midland (ADM), and Cargill. I watched it develop working for Onan / Cummins.
 

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And here I was doing to ask if you could tell a difference between 89 and 91.

They still sell 89 octane up here, with 10% ethanol only, state-mandated (as is 87 octane). So, I can tell it runs smoother on 89 / 10 than 87 / 10. Did not try 91 because supposedly the engine won't advance ignition timing further to take advantage of it, and without that it leaves more unburned deposits.

The moral of the story is to run the lowest octane your engine has ignition timing advance setting. Many tuners have a 91 or higher octane power setting that will advance ignition timing further. I have that too, just not interested in a race truck. I use the tow setting which still calls for 89 octane.

Another interesting tidbit in Minnesota - state law allows sale of 91 octane pure gas for sensitive engines - motorcycles, outboards, chainsaws, other 2-strokes, etc. State law prohibits using 91 octane pure gas in modern vehicles, yet there is zero enforcement. Usually there is just one or two pumps of this small engine gas at a station, but stations also sell 91 octane with 10% ethanol for high compression and/or turbocharged engines like wifey's Mazda that prefers it.

Finally, the ethanol mafia in Minnesota bribed the legislature to promote 88 octane with 15% ethanol gas, along with E85 which is 85% ethanol for 'flex fuel' engines. This is all just agri-processor giant bribery of government. Food grown for fuel. The culprits here are Cenex (CHS now), Archer-Daniels-Midland (ADM), and Cargill. I watched it develop working for Onan / Cummins.
I realize that 91 isnt idea either according to fca, and use it anyway, So I certainly don't judge. If 87 ******* timing, what does 91 do? Notice I said if. If 89 is optimal, what is going slightly higher octane do for timing? Yes it wont be an advtange, if so that means 89 would produce same effect I get between the two octanes? Maybe I try 89 some time and let you know.
 

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Hey Brian now I'm curious, I will let gas get low and try 89 from Chevron. The deal at costco isnt great for 91, I bet it is similar price to 89 and chevron. I just use them out of habit more then anything, that plus the gas prices here, every little bit helps. The fact they dont have 89 makes me want to price check that. Thanks, I seriously will update in a while.
 

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Hey Brian now I'm curious, I will let gas get low and try 89 from Chevron. The deal at costco isnt great for 91, I bet it is similar price to 89 and chevron. I just use them out of habit more then anything, that plus the gas prices here, every little bit helps. The fact they dont have 89 makes me want to price check that. Thanks, I seriously will update in a while.

Huh - I though you didn't have 89 around there?
 

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Ok .....I did a couple octane tests. I know the truck 'feels' a little more peppy with higher Octane fuel, but I wanted to see how higher octane would affect the timing. Help me interpret these graphs. Note: I'm not trying to start a war here. Nor is this test scientific I'm sure. Let me know if I'm not reading the right info.

Test 1 - Running 87 Octane 10% ethanol. Moderate driving (not lead foot). Current price: 3.34/gal

Test 2 - Filled up with 91 Octane no-ethanol when tank was about 1/8 tank. Let's say it's diluted down to 89-90 (from the 87 left in the tank). Drove about ~60 miles after fill-up and about 8 on/off's later. Current price for Premium (here): ~4.20/gal. Unfortunately our options around here are 87 Octane (10% Ethanol), 88 (15%) or 91 (0%). We're at 870' above sea level.

I thought the timing numbers between the two tests would come out better on the higher octane fuel. There's better acceleration and overall driving 'feel' with the higher octane, as others have reported. The truck was in the MDS mode most of the time as the driving was on rural country roads. The Base Spark and the Spark Advance graphs and range, between the two tests didn't vary a a whole lot (note: most of Test 1 Spark Advance was around 20 ..depending on the exact moment I took the picture). Even the Knocks and Knock Retard graphs weren't greatly different. Am I missing something? What do you think?

Octane Timing Test 1_87.jpg

Octane Timing Test 2_ 89-90.jpg
 
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HEMIMANN

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Are the top values averages? If so, there's a big difference between those.

For instance, on 87 octane gasoline with 10% ethanol, top number spark advance is 16 degrees BTDC. On your high octane w/o ethanol it is 22.5.

6.5 degree change in avg. spark advance timing is huge.
 

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Are the top values averages? If so, there's a big difference between those.

For instance, on 87 octane gasoline with 10% ethanol, top number spark advance is 16 degrees BTDC. On your high octane w/o ethanol it is 22.5

The larger bold numbers are the 'current' instant numbers. Most of the pictures I took of the 87 octane were around 19-20 or so. Happened to be 16 on that picture. It was difficult to drive, take pictures, get a non-blurry pic ...and not get a glare. And the higher octane varied too. Some pictures it's 19 ..some 22. Even though the pictures were on flat roads (@55) advance varied a little depending on micro-adjustments of the accelerator.
 
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HEMIMANN

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The larger bold numbers are the 'current' instant numbers. Most of the pictures I took of the 87 octane were around 19-20 or so. Happened to be 16 on that picture. It was difficult to drive, take pictures and not get a glare

Thank you for all of this info, btw. Please excuse my lack of manners! Been having a tough day diagnosing my tractor diesel.
 

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Ok .....I did a couple octane tests. I know the truck 'feels' a little more peppy with higher Octane fuel, but I wanted to see how higher octane would affect the timing. Help me interpret these graphs. Note: I'm not trying to start a war here. Nor is this test scientific I'm sure. Let me know if I'm not reading the right info.

Test 1 - Running 87 Octane 10% ethanol. Moderate driving (not lead foot). Current price: 3.34/gal

Test 2 - Filled up with 91 Octane no-ethanol when tank was about 1/8 tank. Let's say it's diluted down to 89-90 (from the 87 left in the tank). Drove about ~60 miles after fill-up and about 8 on/off's later. Current price for Premium (here): ~4.20/gal. Unfortunately our options around here are 87 Octane (10% Ethanol), 88 (15%) or 91 (0%). We're at 870' above sea level.

I thought the timing numbers between the two tests would come out better on the higher octane fuel. There's better acceleration and overall driving 'feel' with the higher octane, as others have reported. The truck was in the MDS mode most of the time as the driving was on rural country roads. The Base Spark and the Spark Advance graphs and range, between the two tests didn't vary a a whole lot (note: most of Test 1 Spark Advance was around 20 ..depending on the exact moment I took the picture). Even the Knocks and Knock Retard graphs weren't greatly different. Am I missing something? What do you think?

View attachment 502614

View attachment 502615
Look at the frequency and hight of ST (Short Term) Knock Retard, that's what the higher octane does for you. The Spark Advance and Base Spark are going to be roughly the same because that's built into the tune of the truck whether it be stock or a custom tune.

Also LT (Long Term) Knock Retard is where things really get bad on 87. Thats the PCM detecting a lot of ST Knock and compensating by pulling timing automatically under certain loads. I have 0 LT Knock Retard when I run 93 but up to 5⁰ of LT Knock.
 

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No problem. You could be right.

I was watching the numbers as I was driving, and taking pictures. The timing probably is better with the higher octane (it HAS to be ...doesn't it?). And maybe the better test would be during acceleration.
 

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Look at the frequency and hight of ST (Short Term) Knock Retard, that's what the higher octane does for you. The Spark Advance and Base Spark are going to be roughly the same because that's built into the tune of the truck whether it be stock or a custom tune.

Also LT (Long Term) Knock Retard is where things really get bad on 87. Thats the PCM detecting a lot of ST Knock and compensating by pulling timing automatically under certain loads. I have 0 LT Knock Retard when I run 93 but up to 5⁰ of LT Knock.

Ok ...I see what you're saying...
 
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No problem. You could be right.

I was watching the numbers as I was driving, and taking pictures. The timing probably is better with the higher octane (it HAS to be ...doesn't it?). And maybe the better test would be during acceleration.
With more acceleration and of course RPMs yes it will be better ...

I am going to show an ex co-worker these screenshots and ask him what he sees, he is all into the timing and retard levels on all MOPARs ...

Also you should take some screenshots going up hills when you are at higher RMPs during kickdown ... I am curious to see what it does then ...
 

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Also you should take some screenshots going up hills when you are at higher RMPs during kickdown ... I am curious to see what it does then ...

Thanks. I can do that. I don't get into the timing as much as some of the other guys on this forum. I'm all ears on your ideas. Currently I have the high-octane in the tank. I probably should have done some acceleration readings when I had 87 in it.
 

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Look at the frequency and hight of ST (Short Term) Knock Retard, that's what the higher octane does for you. The Spark Advance and Base Spark are going to be roughly the same because that's built into the tune of the truck whether it be stock or a custom tune.

Also LT (Long Term) Knock Retard is where things really get bad on 87. Thats the PCM detecting a lot of ST Knock and compensating by pulling timing automatically under certain loads. I have 0 LT Knock Retard when I run 93 but up to 5⁰ of LT Knock.

Would you mind explaining a little further? I didn't see a datalog labeled LT Knock Re*****. What is the difference between ST & LT?

Isn't timing adjusting exactly what is desired between different octanes? I think you're saying default timing is advanced for 89 octane all the time until knock is detected and then it re*tards the timing? Why is that bad if the reaction is quick? Yeah, we get full benefit of the default advanced timing with 89 octane (supposedly no more for 91 octane) of more power and less fuel consumption, but does that necessarily imply 87 octane is 'bad'?
 

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Would you mind explaining a little further? I didn't see a datalog labeled LT Knock Re*****. What is the difference between ST & LT?

Isn't timing adjusting exactly what is desired between different octanes? I think you're saying default timing is advanced for 89 octane all the time until knock is detected and then it re*tards the timing? Why is that bad if the reaction is quick? Yeah, we get full benefit of the default advanced timing with 89 octane (supposedly no more for 91 octane) of more power and less fuel consumption, but does that necessarily imply 87 octane is 'bad'?
Absolutely. So on his log there was only ST Knock and its unclear how much timing it was pulling on ST Knock. There was no LT Knock on his log unfortunately, that would've told us a lot.

This is as I understand it, I'm not tuner by any means lol.

The default timing is based on timing tables that the pcm reads based on aircharge vs rpm. There's actually several tables it uses to determine what timing to use, octane has little to no bearing on what values the pcm uses for these tables. A custom tune modifies these tables so the values are higher on certain areas of those tables which results in more power and the requirement of higher octane fuel to prevent knock. Some Tuners cheat and also desensitize the Knock sensors which isn't good.

ST Knock vs LT Knock.

ST Knock is what the PCM pulls on demand as Knock occurs. The Knock sensors detect Knock, the pcm pulls timing and it's displayed as the ST Knock pid. If the spark advance is 25⁰ and ST Knock is 3⁰, the actual spark advance is 22⁰ at that point. As Knock disappears the PCM adds back that 3⁰ and the Spark Advance is back to 25⁰. Keep in mind the spark advance changes on the fly, this is just an example.

LT Knock is the PCMs way of PREVENTING Knock from occurring after its occurred at the same throttle point/engine load. So lets say Knock occurs consistently at 1300rpm at 30% throttle above 70% engine load (ex. cruising on the highway giving it light throttle up a hill) and ST Knock is consistently 3⁰. The PCM will see that Knock is occurring during those conditions and pull 3⁰ when those conditions occur. That way Knock isn't occurring, but at the cost of timing. So let's assume 25⁰ timing, if you were looking at Spark Advance/LT/ST Knock on a scantool, during a LT knock situation you would see ST Knock at 0 (no actual knock occuring), LT Knock at 3⁰ (PCM Automatically pulling 3⁰) and Spark Adv go to 22⁰ under those conditions and remain at 22⁰ for much longer. Long story short, ST Knock is when Knock is actually occurring, LT Knock is the PCM trying to prevent Knock. If it's really bad knock, you can have both ST and LT at the same time and then the PCM will increase LT to stop ST.

So while running 87 you will get Knock at first and then the pcm will just pull timing to prevent it. That's when you lose power and fuel economy. On 91/93 there is less ST Knock so the PCM doesn't need to automatically pull timing (LT Knock) to prevent knock from happening.

Hopefully that made sense and I didn't just ramble lol

As for 89 vs 93, I've noticed a pretty big reduction in LT while running 93 vs 89. Virtually 0 LT on 93, only time I saw LT with 93 was towing my camper up a mountain and it was only 1⁰. On 87 I've seen up to 8⁰ of LT with some ST still occurring just driving to work. That was the last time I ran 87 in my truck.
 
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Docwagon1776

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Like others I only use 87! My operators manual says 87 or 89. I assume that the computer (based on a knock sensor) will just back the timeing down if it needs to. So you might give up a few HP if it does. Are they necessary?

Some guys buy the V6, so probably not necessary.

Personally, I bought the Hemi on purpose.
 

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@ramffml - thanks very much for the tutorial. I need to read and digest, ponder, I may have another question. I was promoted to leading project just as digital tuning was starting so I don't know all these details.

I appreciate your sharing!
 

ramffml

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@ramffml - thanks very much for the tutorial. I need to read and digest, ponder, I may have another question. I was promoted to leading project just as digital tuning was starting so I don't know all these details.

I appreciate your sharing!

I'd like to take credit for that very valuable post from @Hemi395 but it wasn't mine :). I am learning this as he posts it as well.
 
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