87 or 89 octane

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seabrook

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I use the Diablosport Trinity to log ST/LT knock. Like I said, even on 93 I was getting knock which reduces timing/power.

This isnt just one vehicle either... It was my 09 5.7 1500, my 2012 5.7 1500, my 2013 5.7 Challenger, my GF's 13 v6 Charger, her v6 Jeep and now my 20 1500 5.7. Every single one of those got high ST or LT knock on 93 octane. I live in Texas so the heat has something to do with it but I have a 180 therm on my Challenger and it was still happening. I installed catch cans on all of them and instantly saw a reduction in knock.

The fact is, you will not know if your engine is reducing timing due to knock as its not always audible. You have to either log it or do the octane test with a few tanks to see if your MPG increases as your octane increases. Thats a clear sign that the lower grade is causing timing reduction.


knew it i tell these guys all the time, yeah it will run on 87/89 but at reduced performance and you going to have some knock and to have reduced performance the knock has to happen. so all the are doing is putting in knock sensors and adjusting the timing according to the knock- it's a feedback loop.... thats why i run 93 and like noted above 93 will knock (i worked in a knock room) but at a much reduced rate (less than a percent) than 87/89 and you get full timing until it gets hot and you get a knock
 

Fatbob Frank

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I'm not even sure 89 actually exists...
I've never seen it.
We have 87 with or w/out 10% eth. We have 88 ( which I recently found out was E15)
or we have 91 no eth and it costs $.40/gal more than diesel.
So 87 is really my only option and what I've always used.
Regular 87 is $.40/gal more than 10%eth but I'm going to run it for a couple tanks and see if it's worth the extra $$$ in added mileage...
So far I'm only seeing about a 1mpg increase...
 

HEMIMANN

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Yes, we have 89 octane here in the upper midwest USA. They are pushing tax-subsidized 88 octane 15% ethanol, so don't be fooled into that. Harder on elastomers (higher solvency), lower energy content, etc.

Only run the highest octane recommended or needed for the ECM mapping. Running any higher leads to uncombusted fuel residue (deposits). I worked in engines and powertrain for 32 years.
 

2012RAM1500RT

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I use to push 93 octane like the Holy Bible especially in older cars and no one could tell me different. Since gas has changed to .70 cent higher between 87 octane to 93 octane it has made me try others. I have a Diablo tuner with a Hemifever 87 tune and 93 tune and a Vararam CAI and nothing else. I haven't heard one sign of a spark knock running the 87 octane tune as of 6000 miles. He suggested when I want to run the 93 tune to run 2 tanks of 93 octane through it before using the 93 tune. Well I planned on doing that before I went to Rockingham Dragway Mopar Show on April 3 2021 so I could tune it but I never got the time to run any through before the date came so I was forced to go with 87 octane and 87 tune. I got to run 2 test runs in the 1/4 mile before they started running ET'S and I got eliminated in the 3rd round. Never ran this truck in the 1/4 mile before but my first run was a 14.5 and every time I ran I got better or it got faster on every run. I only won the first 2 times because the others red lighted. The 3rd time I broke out and the other guy knew what he was doing. Anyway my final run I had gotten down to a 14.1 and didn't get to run anymore. I hope sometime soon I'll get to find out what it will run with the 93 tune but was pretty happy with running that with 87 and NO knocking. If I done my figuring right I will have to get 6 more miles to the gallon running 93 to break even on the cost difference. If I hear a knock or ping just one time I will up my octane to 89 and even go to 93 if necessary. Not going to hurt my engine from it spark knocking at any fuel cost. I say test your vehicle and run what's best for your engine and wallet. I'm not disputing higher octane isn't somewhat better just that it isn't better enough for me to use it consistently.
 
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HEMIMANN

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Depends how sensitive the knock sensors are. I suspect knock doesn't need to be human-audible for the sensor to pick up a spike in combustion pressure higher than smooth combustion, and ******* spark timing accordingly.

Presuming this is the case, you can run any octane you want. You'll get maximum torque and mileage with the highest allowable octane. That's just physics. But don't use high than the owner's manual recommends because the ECM won't advance the spark timing to completely combust it. Then you get deposits.
 

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if you run 87/89 you are knocking and getting a reduction in timing your compression ratio is 10.5(compression x 10 = 105 at max timing) so to run these octanes safely they reduce timing not to mention that 89 is just a pre-determined mix at the gas station between 87 and 93- the refinery does not make 89 so you are depending that that ratio be correct...... so that's why i say 87/89 you are knocking. so i'm getting everything (stock timing (tune) is optimized at 89 not max) by running 93.
 

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if you run 87/89 you are knocking and getting a reduction in timing your compression ratio is 10.5(compression x 10 = 105 at max timing) so to run these octanes safely they reduce timing not to mention that 89 is just a pre-determined mix at the gas station between 87 and 93- the refinery does not make 89 so you are depending that that ratio be correct...... so that's why i say 87/89 you are knocking. so i'm getting everything (stock timing (tune) is optimized at 89 not max) by running 93.

How can you say our engines are knocking even on 89, which is what the ECM is pretty much tuned to? I don’t know what they do in the stock tune to say 89 is recommended but 87 is ok but on 89, I don’t get how there would be any knocking if that’s what the computer is tuned to run on.

And how do you know what the pumps are set up to to get the 89 they sell? Also, here in Oklahoma, I’ve yet to see a station that sells 93. They sell 91, but not 93. If you venture down into Texas, they sell 87/89/93 but not here. I Why shouldn’t I trust the pump to thoroughly blend the 87 and the 91 to make proper 89 octane fuel?

I still don’t understand how you think you’re getting everything you need at 93.


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2012RAM1500RT

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Not going to get into if a tree falls in the forest does it make a sound if no one is there story, but mine doesn't knock by my ears which works for me. Going to start using 89 for a while just to see if there is any MPG difference. I never deny higher octane is better, how much or worth it is the question.
 
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seabrook

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How can you say our engines are knocking even on 89, which is what the ECM is pretty much tuned to? I don’t know what they do in the stock tune to say 89 is recommended but 87 is ok but on 89, I don’t get how there would be any knocking if that’s what the computer is tuned to run on.

And how do you know what the pumps are set up to to get the 89 they sell? Also, here in Oklahoma, I’ve yet to see a station that sells 93. They sell 91, but not 93. If you venture down into Texas, they sell 87/89/93 but not here. I Why shouldn’t I trust the pump to thoroughly blend the 87 and the 91 to make proper 89 octane fuel?

I still don’t understand how you think you’re getting everything you need at 93.


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i don’t trust that it is actually 89- is that clear enough lol
 

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i don’t trust that it is actually 89- is that clear enough lol

I pretty much already kind of gathered that which is why I was curious why you don’t trust it. That’s supposed to be calibrated equipment to blend those two fuels.

I guess I’m just too much of a firm believer in going over what you’re programmed for isn’t good either because the octane of the fuel is outside what the ECM can adjust timing for which causes deposits.


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seabrook

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I pretty much already kind of gathered that which is why I was curious why you don’t trust it. That’s supposed to be calibrated equipment to blend those two fuels.

I guess I’m just too much of a firm believer in going over what you’re programmed for isn’t good either because the octane of the fuel is outside what the ECM can adjust timing for which causes deposits.


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i work for Marathon and knowing what goes into just staying on spec in a unit with the average cost of 30-50 million per unit for the control system to control it... that little mixing pump... yeah i dont buy that is working correctly. so the difference from plus to premium is peenies so that's why i say i do 93 heck stations at one time were getting busted for sell 87 labeled as 93- that's a big moneymaker!
 

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Maybe things have changed in the last few years but usually the only thing a higher octane fuel does for you is just take a few more bucks out of your wallet.

A bit late to the game here, but yes, things have changed. At least around here, most gas is 10+% ethanol. Several brands offer their 91/93 as E0, and I will pay the extra for real gasoline.

Frankly, the cost of gasoline is relatively small compared to the total cost of ownership if we are talking about buying new or near new. The IRS considered the TCO at $0.56/mile. Even at 15 MPG an increase of $0.25/gallon, fuel costs increase about 1.5 cents per mile.
 

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i don’t trust that it is actually 89- is that clear enough lol

Well you can always take a few ounces and test it. I think all you need is something like a doctorate in chemical engineering and $12mm in equipment.
 

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Just one more point.

Higher octane means it doesn't burn as easily.

Think about that for a few minutes and comment/question as it suits your personality.
 

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Just one more point.

Higher octane means it doesn't burn as easily.

Think about that for a few minutes and comment/question as it suits your personality.


Which is why higher octane gasoline REQUIRES matching advance spark ignition timing to combust as completely as possible. I'm starting to sense peeps aren't listening. So, when Ram tells us 89 octane is recommended, they mean any higher octane will not burn as well, leaving deposits and wasting money at the pump.
 

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Which is why higher octane gasoline REQUIRES matching advance spark ignition timing to combust as completely as possible. I'm starting to sense peeps aren't listening. So, when Ram tells us 89 octane is recommended, they mean any higher octane will not burn as well, leaving deposits and wasting money at the pump.

naa wont hurt anything- 93 is better sorry
 

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i work for Marathon and knowing what goes into just staying on spec in a unit with the average cost of 30-50 million per unit for the control system to control it... that little mixing pump... yeah i dont buy that is working correctly. so the difference from plus to premium is peenies so that's why i say i do 93 heck stations at one time were getting busted for sell 87 labeled as 93- that's a big moneymaker!

On that part, you’re just talking about a scamming gas station, nothing more, nothing less.

But how hard is it, seriously, for a modern computerized gas station pump to draw out a specific amount from the 87 octane and the 91/93 octane underground tanks and blend it as it goes into the hose that fills your gas tank?

I think you’re breathing way too much into it and most importantly, it’s a well known fact that with today’s modern cars, you have to run an octane that the car is programmed to run on, unless you retune the computer for it.

https://auto.howstuffworks.com/gas-pump.htm


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corneileous

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Which is why higher octane gasoline REQUIRES matching advance spark ignition timing to combust as completely as possible. I'm starting to sense peeps aren't listening. So, when Ram tells us 89 octane is recommended, they mean any higher octane will not burn as well, leaving deposits and wasting money at the pump.

That’s just like with anything, really. If it says 87 in the book, nothing is magically gonna happen on hotter fuel.


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