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2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
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Discussion Starter · #1 ·
Just finished comparing 2 tanks of 87 to two tanks of 89. In trying to get a 0-60 comparison I got 7.x with the 87 and 6.6 with the 89. In terms of drivability, the 89 definitely seems to produce a smoother power flow. As best I could I watched the ignition advance thru the OBD port and there seems to be about a 5 degree retardation overall with the 87. Seat of pants is that with the 87 the engine is always bouncing the advance around as it senses pinging and you feel it in the power delivery. The power delivery just seems livelier, steadier, and more put together with the 89. Even the shifts seem smoother with the 89. With the 87 some shifts seem to cause the engine to retard making it feel like the shift itself isn't very smooth. There might have also been a 1 or 2 mpg increase with the 89 but that's pretty hard to judge.
 

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Just finished comparing 2 tanks of 87 to two tanks of 89. In trying to get a 0-60 comparison I got 7.x with the 87 and 6.6 with the 89. In terms of drivability, the 89 definitely seems to produce a smoother power flow. As best I could I watched the ignition advance thru the OBD port and there seems to be about a 5 degree retardation overall with the 87. Seat of pants is that with the 87 the engine is always bouncing the advance around as it senses pinging and you feel it in the power delivery. The power delivery just seems livelier, steadier, and more put together with the 89. Even the shifts seem smoother with the 89. With the 87 some shifts seem to cause the engine to retard making it feel like the shift itself isn't very smooth. There might have also been a 1 or 2 mpg increase with the 89 but that's pretty hard to judge.
Interesting feedback, did you take account the outside temps during both tanks? I wonder how the V6 would compare between 87 and 89...
 

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2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
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Discussion Starter · #3 ·
Interesting feedback, did you take account the outside temps during both tanks? I wonder how the V6 would compare between 87 and 89...
It was actually hotter during the 89 octane tanks. I think the V6 specifies 87 octane so you probably wouldn't feel any difference. Might even perform slightly worse on 89 although I don't think it would have drivablity issues.
 

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I also noticed that the ride/shifts were smoother using 89 vs 87 but I thought it might have been in my head... maybe not
 

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Interesting feedback, did you take account the outside temps during both tanks? I wonder how the V6 would compare between 87 and 89...
From my very unscientific tests, in the V6 running Regular Unleaded which is 85 octane here and mid to high octane 87 to 91 as well as 88 octane E0, there wasn't really any difference I could find. I didn't do any 0-60 tests. The MPG was within the standard deviation I normally would see. Nothing jumped out as better so I just run the regular 85 here or 87 at lower altitudes.
 

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From my very unscientific tests, in the V6 running Regular Unleaded which is 85 octane here and mid to high octane 87 to 91 as well as 88 octane E0, there wasn't really any difference I could find. I didn't do any 0-60 tests. The MPG was within the standard deviation I normally would see. Nothing jumped out as better so I just run the regular 85 here or 87 at lower altitudes.
I get more variation just changing brands of midgrade.
Winter/Summer blends also change mileage.
The local stuff is all high altitude, but it appears not all highs are created equal, and "top tier" typically means you pay extra for a little badge on the pump that your engine cannot see.
 

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2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
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Discussion Starter · #7 ·
I also noticed that the ride/shifts were smoother using 89 vs 87 but I thought it might have been in my head... maybe not
I'd have to assume that my seat of the pants does feel something. It seems unlikely FCA would spec 89 if it ran exactly the same on 87. People with a very light foot might not notice a difference in normal everyday driving though. I like to accelerate.
 

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I'd have to assume that my seat of the pants does feel something. It seems unlikely FCA would spec 89 if it ran exactly the same on 87. People with a very light foot might not notice a difference in normal everyday driving though. I like to accelerate.
Long gone are the days when we could rotate the distributor cap to advance or retard spark to give us some extra oomph, but being careful not to create knock in the process. Now, the computer does all of that on the fly. The computer really doesn't know whether you put 87 in it or 100 AVGas; it knows whether the engine is starting to knock and automatically adjusts accordingly. So, if your computer is tuned for 89, it can handle 87 and probably 85 in a pinch, but something else has to go to manage that. That something else is usually a bit of power and/or economy. Normally the difference between 89 and 87 would be minor, but there would be a difference.

We have this discussion over on Miata.net all the time. Mazda recommends 91, but Miatas will run fine on 87 if you aren't racing them.
 

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Well if the owner manual says it can handle it, cause the PCM is tuned to use both Octanes. But to be honest, most vehicles the knock protection will probably save you if you do use a few numbers lower octane than the O.M. calls for, but no one can guarantee it. There are a few cars out there, it might not.

The knock protection, is designed and tested for using the recommended octane and encounter the rare occasion you still get detonation/knock. It merely retards timing for a few seconds and goes back to normal.

It was never designed or tested to protect against the driver using a lower than recommended octane. Sure, in most motors it might work and protect the motor, and retarding timing so often may end up lowering the MPG. Some it might not, and the motor could suffer damage.

Now we have the 89 Octane recommended for best performance, 87 Octane is acceptable. When you have this "dual tune" type feature, its taking the knock sensor to a whole other level. It's not retarding timing for a few seconds if it senses knock. It's looking for different kinds and levels of knocks, it makes tuning adjustments for much longer, like minutes and hours, not seconds and then keeps testing to see if it can go to the more aggressive tune and not get a knock, etc, etc....

If you drive at higher altitudes, you can safely use a lower octane. People posting they can only get 85 or 86 octane in their area and don't have problems, so surely everyone can use it also, don't bother to tell you they live in the mountains 6k feet above sea level. Lower ambient air pressure means lower cylinder pressures and thus less propensity to knock, it also why the engine performs worse. Someone at Sea Level tries to do the same thing, they could get knock.
 

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Discussion Starter · #10 ·
Was down to half a tank so filled up with 12 gallons of 87. That gave me an average octane of 88 when mixed with the 89 already in the tank. Feels like it's on the ragged edge of wanting more octane. Not as bad as when its straight 87 but not a smooth a powerflow as it had on all 89. Amazing what one octane point can do.
 

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From my very unscientific tests, in the V6 running Regular Unleaded which is 85 octane here and mid to high octane 87 to 91 as well as 88 octane E0, there wasn't really any difference I could find. I didn't do any 0-60 tests. The MPG was within the standard deviation I normally would see. Nothing jumped out as better so I just run the regular 85 here or 87 at lower altitudes.
From the owners manual for the 3.6.

“Use of gasoline with an octane number lower than 87 can cause engine failure and may void or not be covered by the New Vehicle Limited Warranty.”

Use of anything less then 87 has a higher chance to cause “engine knocking” which over time will cause engine failure.
 

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From the owners manual for the 3.6.

“Use of gasoline with an octane number lower than 87 can cause engine failure and may void or not be covered by the New Vehicle Limited Warranty.”

Use of anything less then 87 has a higher chance to cause “engine knocking” which over time will cause engine failure.
At around 4200 feet above sea level and higher 85 is equivalent to 87 at sea level. When I am traveling at lower altitudes I run 87.
 

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All else equal, does a car get better mileage at higher altitude? That seems counter-
intuitive to me, but I still can't get over the fact that the 3.6L GC I rented for a thousand miles in the Yellowstone area back in 2014 averaged 28mpg for the whole time I had it.
 

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All else equal, does a car get better mileage at higher altitude? That seems counter-
intuitive to me, but I still can't get over the fact that the 3.6L GC I rented for a thousand miles in the Yellowstone area back in 2014 averaged 28mpg for the whole time I had it.
I think at slower speeds, lower load the engine uses less fuel due to less air at altitude, but at higher speeds and under larger loads the engine has to work harder due to making less power then under the same conditions at sea level.
 

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Discussion Starter · #15 ·
All else equal, does a car get better mileage at higher altitude? That seems counter-
intuitive to me, but I still can't get over the fact that the 3.6L GC I rented for a thousand miles in the Yellowstone area back in 2014 averaged 28mpg for the whole time I had it.
Perhaps you were blessed with real gasoline up there instead of the alcohol laced crap we are normally saddled with.
 

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Discussion Starter · #16 ·
Was down to half a tank so filled up with 12 gallons of 87. That gave me an average octane of 88 when mixed with the 89 already in the tank. Feels like it's on the ragged edge of wanting more octane. Not as bad as when its straight 87 but not a smooth a powerflow as it had on all 89. Amazing what one octane point can do.
Another update. Got sick of it being on the ragged edge of running 100% proper so when it was down to 2/3 full I filled it up with 91 octane. Now it feels like it's really running properly again.
 

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I am a new GC owner. Mine is a 2014 3.6L v6 Limited Flex Fuel one and have been filling only 87 Octane . Since i bought a used car i didnt get the Manual with it..

I do feel some knocking once in a while and want to give 89 a try too


For 3.6L V6

This engine is designed to meet all emissions
regulations and provide excellent fuel
economy and performance when using
high-quality unleaded “regular” gasoline
having an octane rating of 87. The use of
premium gasoline is not recommended, as it will not
provide any benefit over regular gasoline in these engines


For 5.7L

This engine is designed to meet all emissions
regulations and provide satisfactory
fuel economy and performance when using
high-quality unleaded gasoline having
an octane range of 87 to 89. The manufacturer
recommends the use of 89 octane for optimum
performance. The use of premium gasoline is not recommended,
as it will not provide any benefit over regular
gasoline in these engines.
JEEP GRAND CHEROKKE MANUAL
 

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I am a new GC owner. Mine is a 2014 3.6L v6 Limited Flex Fuel one and have been filling only 87 Octane . Since i bought a used car i didnt get the Manual with it..

I do feel some knocking once in a while and want to give 89 a try too


For 3.6L V6





For 5.7L



JEEP GRAND CHEROKKE MANUAL
Ok, are you sure you're getting pre-ignition detonation? Cause unless you're in death valley, I can't imagine why you would be getting pre-ignition or detonation, unless you have a malfunction. Lots of things can cause a knocking noise.

Southern California had a scandal going when I lived there years ago, where they were selling cut rate quality gasoline that was below the listed octane. I did run 89 octane instead of 87 at that time.
 

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Just finished comparing 2 tanks of 87 to two tanks of 89. In trying to get a 0-60 comparison I got 7.x with the 87 and 6.6 with the 89. In terms of drivability, the 89 definitely seems to produce a smoother power flow. As best I could I watched the ignition advance thru the OBD port and there seems to be about a 5 degree retardation overall with the 87. Seat of pants is that with the 87 the engine is always bouncing the advance around as it senses pinging and you feel it in the power delivery. The power delivery just seems livelier, steadier, and more put together with the 89. Even the shifts seem smoother with the 89. With the 87 some shifts seem to cause the engine to retard making it feel like the shift itself isn't very smooth. There might have also been a 1 or 2 mpg increase with the 89 but that's pretty hard to judge.
Quick question. I have a 2019 GC Limited 5.7L with a custom exhaust and air filter. I live in Colorado where we only have 85-87-91 gas types. To get the closest to 89 octane performance on this jeep, would it better to run 87 or 89? This is a performance question, while ensuring no damage happens to the engine. Not a price question.
 

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Quick question. I have a 2019 GC Limited 5.7L with a custom exhaust and air filter. I live in Colorado where we only have 85-87-91 gas types. To get the closest to 89 octane performance on this jeep, would it better to run 87 or 89? This is a performance question, while ensuring no damage happens to the engine. Not a price question.
I live in Salt Lake City so we have the 85-87/88/89-91 octane depending on station. I will generally run the mid grade, depending on the station it could be 87, 88, or 89. The chevron I usually go to has 87 octane E-0, or 88 octane E-10....I have run both. Maverik stations have 85, 87, 89, 91....I will usually opt for the 87. If its really hot out I may go back and forth between the 87 and 89. I think if you just go mid grade you'll be fine. I've run a few tanks on 85 in colder weather as well, I didn't notice much of a difference. In the hot months i tend to only run the mid grade.
 
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