For the guys who think they get more power with 91 octane fuel

JC4041 · Nov 7, 2022

CheechDogg.0n37s said:
I seriously doubt you are getting better MPGs with 87 but I will give you the benefit out of the bout lol ..

As to you not experiencing lack of performance, ok I will say you probably don't notice it , but I guarantee you that if you switch it up to 91 you will definitely feel the difference ... you will see what the HEMI engine is supposed to fee like opposed to being ******** by the lower dirty 87 and 89 octane ...

Again just to save a few bucks to me it's not worth it ... those people who choose to go with lower octane gas to save money are the ones that drive the speed limits and don't ever feel or experience the capabilities of these trucks and cars ... thus they are driving in a way that is also going to save them money ....

Those of us who really don't mind spending the money on 91 or even 93 like someone just stated probably drive these trucks without care or much care for MPGs .... I like to feel the full potential of my truck's HEMI, I don't mind spending the extra money to get that.

So to make it a little more clear for those that might of gotten confused, most people that want to save money use lower octane gas, 89 or 87 ... those same people won't drive their vehicles like people who don't care about the gas prices and love to drive their vehicles to experience full potential ... Those people who want to save money will never really notice their engines knocking because they are not being pushed to the limits or near the limits, so you really can't tell that the knocking is happening anyways because those vehicles are already being driven to save money lol ....got it? ok ...

Does the Fuel You Choose Matter? | Engine Masters | MotorTrend

Does fuel really matter for your engine? Watch as the Engine Masters team takes a scientific look at just how much power and performance are produced by diff...

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tidefan1967 · Nov 7, 2022

JC4041 said:
Why are you wasting money?

View attachment 506290

Those are the "you need to change these plugs at 30k miles" from my '09.....That I changed at 92k miles

Literally made no difference in mileage.
View attachment 506291

Did you check the gap on those? Looks pretty big to me.

JC4041 · Nov 7, 2022

tidefan1967 said:
Did you check the gap on those? Looks pretty big to me.

Those were the factory ones.

clayinfla · Nov 7, 2022

I am definitely trying different fuel on my next fill up. My 2020 is running extremely rough on cold startup (Florida- not that cold). It shudders and shifts anytime I accelerate. Throwing CIL periodically for cylinder 5 misfire. Dealer sees no problem.

Elkman · Nov 7, 2022

The btu's available from 91 octane gasoline is not higher than for 87 octane gas. The engine computer that controls spark advance will retard it to prevent pre-ignition or "knock".

If an engine is carboned up in the cylinders then a higher octane gas may help but this is a very rare situation.

When someone says they get more power from the 91 octane for their truck with its engine designed for 87 or 89 octane gas, then either their is a problem with the lower octane gas from the refiner, which is easy to believe as this is not monitored by the feds so cheating is very easy and no one could accuse the oil companies of ethical conduct, or it is in the driver's head, i.e. the placebo effect.

The amount of ethanol added would have a great deal of impact as there is a lower btu value for this fuel. Actually more energy is used to produce ethanol than it provides in our cars and trucks but when the USA with its massive corn subsidies (at taxpayer expense) produces twice as much corn as people or livestock can eat, then the push to make it into ethanol and keep the subsidy money rolling in.

blackbetty14 · Nov 7, 2022

Wild one said:
Check out post #7. I'm not even going to comment on your idea of " runs like a rap'ed ape" as apparently you have a differant opinion of what it means from the majority of us,

Apparently 4.88 gears in a 6500lb truck with big heavy wheels/tires and no otherwise power mods means ***** ape lol.

blackbetty14 · Nov 7, 2022

Elkman said:
The btu's available from 91 octane gasoline is not higher than for 87 octane gas. The engine computer that controls spark advance will retard it to prevent pre-ignition or "knock".

If an engine is carboned up in the cylinders then a higher octane gas may help but this is a very rare situation.

When someone says they get more power from the 91 octane for their truck with its engine designed for 87 or 89 octane gas, then either their is a problem with the lower octane gas from the refiner, which is easy to believe as this is not monitored by the feds so cheating is very easy and no one could accuse the oil companies of ethical conduct, or it is in the driver's head, i.e. the placebo effect.

The amount of ethanol added would have a great deal of impact as there is a lower btu value for this fuel. Actually more energy is used to produce ethanol than it provides in our cars and trucks but when the USA with its massive corn subsidies (at taxpayer expense) produces twice as much corn as people or livestock can eat, then the push to make it into ethanol and keep the subsidy money rolling in.

Ethanol has lots of benefits over non ethanol gas plus it doesn't smell terrible out the exhaust. Heat is the main cause of detonation/knock and combine that with Timing and cylinder pressure and you get detonation. Ethanol in 50% and higher blends has a huge difference in not only the octane rating of the fuel but the temperature in the air as its vaporized. As ethanol blends increase you get a drop in mileage due to the BTU reduction but gain everywhere else. Boosted guys can run non inter-cooled systems as the reduction in temp is that drastic. As you drop the temps you remove one of the key components of knock/detonation which allows you to add timing if required. Add in something like E85s octane at 117, E75 =111 and pure ethanol is 122. When I tune for E85 I usually have to increase fuel (VE) by 30% and this is due to reduction of BTU. You want the best of both worlds? Run 87 and save your pennies, then take some of those pennies and use a cheap water/**** injection system and let it hit right before peak tq and run the cheapest -20 wiper fluid you can find (30% ethanol by volume). You will instantly get superior detonation control via temp reduction, steam clean the chamber by removing carbon and an added octane rating of 10+ points. AND keep your BTU and thus gas mileage.

Requiring more energy to produce? Perhaps, but just about anything we have in place currently does the same. Solar, EV charging, Wind farms, Electrification are all more inefficient than what is required to produce and maintain.

I'm with the run 87, drive a truck like its a truck and stay off the fake meds.

HEMIMANN · Nov 7, 2022

Elkman said:
The btu's available from 91 octane gasoline is not higher than for 87 octane gas. The engine computer that controls spark advance will retard it to prevent pre-ignition or "knock".

If an engine is carboned up in the cylinders then a higher octane gas may help but this is a very rare situation.

When someone says they get more power from the 91 octane for their truck with its engine designed for 87 or 89 octane gas, then either their is a problem with the lower octane gas from the refiner, which is easy to believe as this is not monitored by the feds so cheating is very easy and no one could accuse the oil companies of ethical conduct, or it is in the driver's head, i.e. the placebo effect.

The amount of ethanol added would have a great deal of impact as there is a lower btu value for this fuel. Actually more energy is used to produce ethanol than it provides in our cars and trucks but when the USA with its massive corn subsidies (at taxpayer expense) produces twice as much corn as people or livestock can eat, then the push to make it into ethanol and keep the subsidy money rolling in.

Unfortunately, that's not how it works - the default ignition timing setting is advanced for 89 octane. If using 87 octane, the PCM has to DETECT knock 1st before it pulls timing back.

There is a big datalog thread showing how it actually does so. At first, it goes into "Short Term" timing adjustment, repeatedly allowing knocking and timing adjust for an unknown number of cycles before it goes into "Long Term" timing adjustment, for an unknown number of cycles.

In essence, the control algorithm ALLOWS repeated episodes of knocking in order to adjust the timing. That's not good. Use 89 octane.

Zac1 · Nov 7, 2022

I live in Utah. Our gas price one of the highest with exception of CA and few others. Not all stations have 87. Ones do it cost you more than 91 at Costco. Reson I use 91 Costco because it is Ethonal free. I try to stay away from Ethanol in all my cars and power equipment.

Jebb · Nov 7, 2022

Elkman said:
The btu's available from 91 octane gasoline is not higher than for 87 octane gas. The engine computer that controls spark advance will retard it to prevent pre-ignition or "knock".

If an engine is carboned up in the cylinders then a higher octane gas may help but this is a very rare situation.

When someone says they get more power from the 91 octane for their truck with its engine designed for 87 or 89 octane gas, then either their is a problem with the lower octane gas from the refiner, which is easy to believe as this is not monitored by the feds so cheating is very easy and no one could accuse the oil companies of ethical conduct, or it is in the driver's head, i.e. the placebo effect.

Exactly. Also, it can take several hundred miles of driving after switching grades of fuel for the PCM to re-adjust trims. And unless you ran your tank dry, several gallons of old fuel mixed with the new fuel - so switching grades shouldn't be instantly noticeable. The change should be gradual and completely unnoticeable by "seat of pants". Actual track data - after sufficient re-adjustment time - is the only real test.

As you said, ethanol has a lower BTU content than gasoline. Anyone who drives an E85 vehicle can tell you how much their mpg drops when running E85. I don't know this for a fact but I suspect some fuel companies pump up their octane rating (perhaps illegally) by adding more ethanol which would produce less mpg at the higher ratings.

My old '04 Hemi Ram owner's manual said to use 89 minimum but my 2017 manual does NOT say that. It runs perfectly fine - even in hot weather up mountain roads - on 87 with no pinging. Before gas went up to $6.00+/gal here I ran a few tanks of 91 but noted no difference other than cost to fill up. If I was pulling a heavy boat or trailer, however, I might run 89/91 JIC.

"Right foot bias" and placebo effect has a lot to do with all of this. If an engine is designed to run on 87 octane running 91 (or 100) will not produce more power.

Jebb · Nov 7, 2022

HEMIMANN said:
... the default ignition timing setting is advanced for 89 octane.

Where did you get this info? My owner's manual does not specify 89 minimum.

Zac1 · Nov 7, 2022

I have 2022 5.7 etorgue. Common gas here is 85. I tried it it ran like crap. Same with 87. I use 91 Cotco ethanol free and it runs great. 91 costco cheaper than 87 brand. If I can, no ethanol for my vehicles.

nascar72 · Nov 7, 2022

Personnaly my 3rd gen hemi runs just fine on 87 octane. The only time I will bump it up to 89 is when I tow my 7 500 lbs 5ft wheel camper or If I'd be driving on hilly roads in the hot summer days. I've tried comparing 91 vs 89 while towing and didn't see any noticeable difference in performance and haven't experienced any knocking with neighter 87 or 89 octane.

HEMIMANN · Nov 7, 2022

Zac1 said:
I live in Utah. Our gas price one of the highest with exception of CA and few others. Not all stations have 87. Ones do it cost you more than 91 at Costco. Reson I use 91 Costco because it is Ethonal free. I try to stay away from Ethanol in all my cars and power equipment.

Any engine with closed loop control can tolerate up to 10% ethanol. Engines without will burn up sooner rather than later. If you have an 2-stroke engines left, never use alcohol in them - they wipe the cylinder walls, break piston rings.

Gary Fields · Nov 7, 2022

My Father was a petrochemical engineer and quite familiar with gasoline and it's qualities. Basically what he told me was that octane is to an engine what water is to the human body. If a human body does not get enough water it does not work right and bad things happen. Once it gets enough water the excess is simply pissed away. Same idea with octane. Don't get enough and it knocks and pings, anything more and it's just .............

97RedRam · Nov 7, 2022

I know this is not scientific but my 97 5.9 has to downshift going up the hills of Tennessee when I use 87 with no ethanol but when I use 91 or 93 no ethanol it will make it up the hills without having to downshift. It appears that with 87 the timing is retarted and with 91 or 93 it is not,

GeoffG68 · Nov 7, 2022

I run 87. No knock, no noticeable difference in power between that and 89. My truck is used as a truck, i.e. carrying and towing heavy loads, rather than just being a big heavy car. It sees WOT semi-regularly. It performs pretty well for what it is: 6,000 pounds of pickup truck.

On the highway, believe it or not, it gets roughly the same MPG at 75 as it does at 85. The difference is too small to see.

I think this is one of those things that varies greatly from motor to motor, drivetrain to drivetrain, and locale to locale. I'm in the Detroit area; we're at around 650 feet of elevation. I've got a 2011 Crew Cab Hemi 4x4 with 3.92s. Maybe the gearing makes a difference. Maybe not. Maybe tire choice makes a difference. Maybe not.

blackbetty14 · Nov 7, 2022

GeoffG68 said:
I run 87. No knock, no noticeable difference in power between that and 89. My truck is used as a truck, i.e. carrying and towing heavy loads, rather than just being a big heavy car. It sees WOT semi-regularly. It performs pretty well for what it is: 6,000 pounds of pickup truck.

On the highway, believe it or not, it gets roughly the same MPG at 75 as it does at 85. The difference is too small to see.

I think this is one of those things that varies greatly from motor to motor, drivetrain to drivetrain, and locale to locale. I'm in the Detroit area; we're at around 650 feet of elevation. I've got a 2011 Crew Cab Hemi 4x4 with 3.92s. Maybe the gearing makes a difference. Maybe not. Maybe tire choice makes a difference. Maybe not.

Gearing increases mechanical leverage on the tire and thus decreases load on the engine. Same goes for the transmission and tq converter... they are all mechanical multipliers and without them an engine wouldn't have enough power to move a car efficiently. Gearing reduces load on the engine which would help with detonation to an extent by working the engine less and creating less heat. Bigger or heavier tires do the opposite or work against the mechanical leverage to spool up which adds load to the engine but once rotating the added mass can help provide coasting power which adds leverage and reduces light engine load. Big weights require more power to move but once moving they are harder to slow down basically.

HEMIMANN · Nov 7, 2022

Jebb said:
Where did you get this info? My owner's manual does not specify 89 minimum.

From the datalog table a member shared with us. Read up.

Further, I did not say 89 octane minimum. I said 89 octane recommended. The manual says 87 minimum. I also said 87 WILL CAUSE knocking.

tidefan1967 · Nov 7, 2022

Hemimann is right, you guys might not be able to hear it knocking on 87 but if you were to check the KR with a tuner/programmer I guarantee you it’s there. Whether it’s actually hurting the engine or not I can’t say.

For the guys who think they get more power with 91 octane fuel

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