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Discussion Starter #1
Lately I have been filling my Jeep (with the 5.7 Hemi) with 89 octane instead of 87. To me, I can feel (I think) the difference with the power and engine response. Anyone else experience this?
 

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2006 WK Overland
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Depends on a lot of things, but quite a bit on the type fuel (must be top tier), weather conditions at the time, how you drive, and the altitude where you drive the vehicle.most. The general rule of thumb is one point less octane needed for every 1000 ft. increase in altitude. On my somewhat modified 06 Hemi Overland (see signature), at an "around home" altitude of about 2400-5000 ft., I run 87 or 89 in the winter and 91 or 93 in the summer, both normally non-ethanol and also depending on weather conditions and the type of driving I am going to be doing.. When I am closer to sea level, I'll run 91 or 93 octane Chevron. When I am above about 5000-5500 ft. elevation and weather conditions are right, I'll even run 85 octane. My best fuel economy ever was 24.3 mpg, running 85 octane between Wells, Nevada and Reno....mostly at an altitude of 5000 ft. or slightly above. Normal highway fuel economy is about 21-23 mpg, running in 4th gear at the sweet spot of about 63-67 mph. The horsepower of my Hemi is somewhere between 425-450. For stock Hemi's the FSM recommends 89, but 87 is acceptable. At most, with the higher octane fuel, the PCM MAY allow a little more timing advance. IMO, any difference in the seat of the pants feel would be almost negligible. Dyno testing would be the most accurate way of telling.
 

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2019 Jeep Grand Cherokee Trailhawk
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Octane is mostly for knock purposes. I live in CO (6.5K elevation) and we're stuck with 85, 87, and 91. All research about 85 is old and I still have no idea why octane ratings aren't standardized across the nation. I've only seen one article where a vehicle manufacturer engineer said to stay away from 85 basically but there's no owners manual I know that specifically talks about high elevation states. I use 91 simply because it's not much more per tank in the grand scheme of things BUT I fully understand it will make little to zero difference in power or mpg...85 octane can eat my ass.
 

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Discussion Starter #4
I don't know what the sea level is here in NY but it must be the placebo effect. I think I feel a difference, but probably not. I have always use 87 octane since I purchased it 7 years ago. Here in NY there is a fifty cent difference from the two octanes. I will switch back to 87 to be economical. Thanks for all the replies!
 

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Wow, something like this gets replies when people are in need of actual fixing issues in their jeeps.

I've had more help in my ford forum about my jeep than here. Not a good experience thus far.
 

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So, go back to your Fix Or Repair Daily or Found On Road Dead forums.I am sure they're very knowledgeable on Jeeps. There are lots of things on all internal combustion engine vehicles that are the same/similar. We don't limit ourselves to just "fixing" issues.....we're a little more broad minded than that.....like helping our fellow Jeepers with anything they're concerned about regarding them. We don't need trolls on here. If you can contribute constructively, in your opinion, why are you on here?
 

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I've been using 87 octane fuel in my GC and have no problems. Same with my F150 with the V8 coyote engine.

One day i decided to try 93 octane in my F150.
It made such a noticeable performance difference i decided to try 93 octane in my GC V6.
With my GC....nothing, same ol same ol waste of money.
If there was a slight performance increase i didn't notice it with my V6.
Maybe 93 octane can noticeably increase performance with the hemi engine?

Only thing i can figure why their was a performance increase using 93 octane in my F150 is that somehow it can figure out what octane fuel is in the tank possibly by sensitive knock sensor feedback then advances the timing algorithm.
 

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I'm not a troll, I ask one question and get plenty of views but no response at all. At least an acknowledgment of said issue.

I'm not knocking anyone, when someone needs help, I do my best to help them.

No reason to be rude about it bro.

It's just when you would expect someone to know the general answer someone would say something.

I've found plenty of people with the same issue, but no one says how they fix it. Just disappear. That's my gripe.

And I'm just stating that others have helped me, when expected others haven't. There was no dissing or intent there.
 

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cattle
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Lately I have been filling my Jeep (with the 5.7 Hemi) with 89 octane instead of 87. To me, I can feel (I think) the difference with the power and engine response. Anyone else experience this?
I have. I've done the "Experiment" comparing performance on 87 vs 89 many times and every single time I can tell the difference immediately. I'm sure there are some people who would not notice because it depends a bit on your driving style. The power flow is just smoother with the 89. With the 87 the engine controls are always on the ragged edge of "normal" versus "retarded due to sub optimum octane"... So the air/fuel map is always being dicked with when you run 87 and it just doesn't run quite as smoothly. They could have designed it for 87 and then you would not notice any difference between 87 and 89 but you also would not be able to get the extra power with 89. As the owners manual says, it was designed for optimum performance on 89 but you can run 87 if you want or need to.
 

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cattle
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Octane is mostly for knock purposes. I live in CO (6.5K elevation) and we're stuck with 85, 87, and 91. All research about 85 is old and I still have no idea why octane ratings aren't standardized across the nation. I've only seen one article where a vehicle manufacturer engineer said to stay away from 85 basically but there's no owners manual I know that specifically talks about high elevation states. I use 91 simply because it's not much more per tank in the grand scheme of things BUT I fully understand it will make little to zero difference in power or mpg...85 octane can eat my ass.
At 6500 feet the 85, 87 and 91 are all you need to be equivalent to 87, 89, and 93 at low elevations. A car the calls for 87 at "normal elevations", i.e. typical low elevation that the vast majority of people live at, will usually run fine on 85 at high elevations. If you are running an unmodified hemi the 87 should work ok and just like 89 would at low elevations. If you had a blower that would not be the case. I have seen some owners manuals that discuss this but most don't. Except for vehicles that need higher than 89 at low elevations it's less confusing to tell people to use the same 87 or 89 no matter what the elevation.
 

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cattle
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I'm not a troll, I ask one question and get plenty of views but no response at all. At least an acknowledgment of said issue.

I'm not knocking anyone, when someone needs help, I do my best to help them.

No reason to be rude about it bro.

It's just when you would expect someone to know the general answer someone would say something.

I've found plenty of people with the same issue, but no one says how they fix it. Just disappear. That's my gripe.

And I'm just stating that others have helped me, when expected others haven't. There was no dissing or intent there.
If you have found plenty of people with the same issue but no one seems to know how to fix it... maybe that means ..... no one knows how to fix it!!!! If no one knows they can't reply and tell you how to fix it. When you complain of others being rude while you are on a free system where people help for free and you are calling out everyone else because they didn't know the answer to your question. THAT seems rude.
 
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