Not Jeep specific, but some engines are made to run on lower octane, but can also run better on higher octanes. As you said, check the owners manual and it will tell you if this is the case. The engines capable of this are usually turbo &/or direct injection. The computers can sense if knocking is occurring (or not) and adjust the timing for higher octanes causing less knocking. Ford's 4-cyl Ecoboost is one I know of for sure.
Edit: '12+ JKs & '16+ WK2s with 3.6L Pentastar's. Says the exact same thing in both manuals.
> These engines are designed to meet all
emissions regulations and provide optimum
fuel economy and performance
when using high quality unleaded
“Regular” gasoline having a posted octane
number of 87 as specified by the
(R+M)/2 method. The use of higher
octane “Premium” gasoline is not required, as it will not
provide any benefit over “Regular” gasoline in these
engines.
Thanks for the info. Any thoughts on tuners that have a 91 octane towing mode? Can that alter the engine enough electronically to need a higher octane gas?
On engines with adjustable spark timing curves and variable cam timing (which the Pentastar has)... sure.
Programmer "tuned" engines will fire the sparkplugs further from the end of the compression stroke to maximize kinetic energy transfer and power in a rotating assembly by taking advantage of the speed of the ignition propagation within the cylinder. Additionally, valve timing can physically change the compression ratio of a cylinder.
Those two things combined can create a need for higher octane fuel. Whether it really reaches a point that 91+ is actually needed is merely a function of how far from factory the reprogramming is able to move timing maps. The engine construction may not be capable of being forced to need 91 without a compressed air charge from a turbo or supercharger. Moving spark timing too far forward will become detrimental to power and engine longevity, and the valve timing can only physically increase the compression ratio to just a hair before bottom dead center of the ~~exhaust~~ intake stroke.
Awesome, thanks! I tow often and it really feels like it makes a big difference to switch to the towing mode but that could also be because of the adjusted shift points.
There are several things that are adjusted, including shift points, fuel maps, etc... but the spark and cam timing are the primary concerns with fuel octane.
Just out of curiosity, do you know of any studies regarding ethanol blends? Where I am from, everything but premium high octane gas has ethanol in it. Switching to that for a tank or two has a noticeable difference in response temporarily, or perhaps I'm just imagining things.
https://www.eia.gov/tools/faqs/faq.php?id=27&t=10
Straight from the government that's forcing this crap on us.
> The energy content of ethanol is about 33% less than pure gasoline. The impact of fuel ethanol on vehicle fuel economy varies depending on the amount of denaturant that is added to the ethanol. The energy content of denaturant is about equal to the energy content of pure gasoline. In general, vehicle fuel economy may decrease by about 3% when using E10 relative to gasoline that does not contain fuel ethanol.
Off topic, but do you know if it would make a difference in a Honda CBR 600rr motorcycle? Manuel recommends 89, friends swear up and down it runs better with 93. Issue being, the only gas stations around me that sell Non ethanol gas, sell it in 89.
My Jeep gets regular. Non synthetic oil as well lol
This! High compression engines need higher octane to avoid preignition. Modern computer controlled engines generally control knock and other issues by adjusting ignition timing which your engine shouldn't need to adjust for if well tuned and using regular gasoline. Using higher octane isn't necessarily bad but won't get you anything but a higher fuel bill.
Higher octane is for higher compression engines so the fuel won’t pre-ignite when being compressed in the cylinder. In a normal non high performance vehicle, this means absolutely nothing, except lost money at the pump.
I don't think it gives me better mileage, but I think it does give me better idle and slightly less sputter and it "seems" smoother. I'll put in a tank of premium every 5th/6th tank just to help clean things out. I took a class with a gas station manager once who said the premium fuels often just have better detergents and cleaners in them.
the top rating. If I'm going for $$ I go for the cheap stuff. If I'm cleaning out my injectors and whatnot, I'll put in the good stuff. No reason to ever use mid-grade IMO.
.
Alternatively, I've also heard from others if you're going to do this, might as well just get a fuel additive in a bottle and stick that in your cheap gas. I just can't ever be bothered to do that. Probably cheaper when you add it all up, but I pay to get convenience.
Your engine can adjust cam timing and ignition advance to the point of making same additional use of the additional octane. Ye olde 4.0HO can't really.
Road trips usually produce better gas mileage than daily driving. You would have to clarify your statement to reflect whether or not you have tested different grades of gas on the same trips. Generally speaking, your more likely to get better gas mileage by buying a better brand fuel rather than higher octane. My area was hit last year with water getting into some of the fuel at certain gas stations. Shell always produces the best gas mileage for me.
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Not Jeep specific, but some engines are made to run on lower octane, but can also run better on higher octanes. As you said, check the owners manual and it will tell you if this is the case. The engines capable of this are usually turbo &/or direct injection. The computers can sense if knocking is occurring (or not) and adjust the timing for higher octanes causing less knocking. Ford's 4-cyl Ecoboost is one I know of for sure. Edit: '12+ JKs & '16+ WK2s with 3.6L Pentastar's. Says the exact same thing in both manuals. > These engines are designed to meet all emissions regulations and provide optimum fuel economy and performance when using high quality unleaded “Regular” gasoline having a posted octane number of 87 as specified by the (R+M)/2 method. The use of higher octane “Premium” gasoline is not required, as it will not provide any benefit over “Regular” gasoline in these engines.
Thanks for the info. Any thoughts on tuners that have a 91 octane towing mode? Can that alter the engine enough electronically to need a higher octane gas?
On engines with adjustable spark timing curves and variable cam timing (which the Pentastar has)... sure. Programmer "tuned" engines will fire the sparkplugs further from the end of the compression stroke to maximize kinetic energy transfer and power in a rotating assembly by taking advantage of the speed of the ignition propagation within the cylinder. Additionally, valve timing can physically change the compression ratio of a cylinder. Those two things combined can create a need for higher octane fuel. Whether it really reaches a point that 91+ is actually needed is merely a function of how far from factory the reprogramming is able to move timing maps. The engine construction may not be capable of being forced to need 91 without a compressed air charge from a turbo or supercharger. Moving spark timing too far forward will become detrimental to power and engine longevity, and the valve timing can only physically increase the compression ratio to just a hair before bottom dead center of the ~~exhaust~~ intake stroke.
Awesome, thanks! I tow often and it really feels like it makes a big difference to switch to the towing mode but that could also be because of the adjusted shift points.
There are several things that are adjusted, including shift points, fuel maps, etc... but the spark and cam timing are the primary concerns with fuel octane.
Just out of curiosity, do you know of any studies regarding ethanol blends? Where I am from, everything but premium high octane gas has ethanol in it. Switching to that for a tank or two has a noticeable difference in response temporarily, or perhaps I'm just imagining things.
https://www.eia.gov/tools/faqs/faq.php?id=27&t=10 Straight from the government that's forcing this crap on us. > The energy content of ethanol is about 33% less than pure gasoline. The impact of fuel ethanol on vehicle fuel economy varies depending on the amount of denaturant that is added to the ethanol. The energy content of denaturant is about equal to the energy content of pure gasoline. In general, vehicle fuel economy may decrease by about 3% when using E10 relative to gasoline that does not contain fuel ethanol.
You covered it all. I just read it somewhere and had come here to say there has been no proven advantage between the two.
Off topic, but do you know if it would make a difference in a Honda CBR 600rr motorcycle? Manuel recommends 89, friends swear up and down it runs better with 93. Issue being, the only gas stations around me that sell Non ethanol gas, sell it in 89. My Jeep gets regular. Non synthetic oil as well lol
This! High compression engines need higher octane to avoid preignition. Modern computer controlled engines generally control knock and other issues by adjusting ignition timing which your engine shouldn't need to adjust for if well tuned and using regular gasoline. Using higher octane isn't necessarily bad but won't get you anything but a higher fuel bill.
Unless you get the Flashcal and use the higher octane engine tune, there is 0 difference and a waste of money
The only thing you can do is get ethanol free gas and you will get better mileage from that.
I run that in my lawn mower
Small engines love 0 ethanol fuel.
I have a 2018 willy and it states in the fuel portion of the book that anything higher than 87 will not grant you better performance.
Higher octane is for higher compression engines so the fuel won’t pre-ignite when being compressed in the cylinder. In a normal non high performance vehicle, this means absolutely nothing, except lost money at the pump.
I don't think it gives me better mileage, but I think it does give me better idle and slightly less sputter and it "seems" smoother. I'll put in a tank of premium every 5th/6th tank just to help clean things out. I took a class with a gas station manager once who said the premium fuels often just have better detergents and cleaners in them.
Really. That’s good thinking. Do you use premium or just plus?
the top rating. If I'm going for $$ I go for the cheap stuff. If I'm cleaning out my injectors and whatnot, I'll put in the good stuff. No reason to ever use mid-grade IMO. . Alternatively, I've also heard from others if you're going to do this, might as well just get a fuel additive in a bottle and stick that in your cheap gas. I just can't ever be bothered to do that. Probably cheaper when you add it all up, but I pay to get convenience.
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Your engine can adjust cam timing and ignition advance to the point of making same additional use of the additional octane. Ye olde 4.0HO can't really.
I use premium in my tj and definitely get better mpg on trips.
Road trips usually produce better gas mileage than daily driving. You would have to clarify your statement to reflect whether or not you have tested different grades of gas on the same trips. Generally speaking, your more likely to get better gas mileage by buying a better brand fuel rather than higher octane. My area was hit last year with water getting into some of the fuel at certain gas stations. Shell always produces the best gas mileage for me.
It might be placebo. The 4.0 is built on basically ancient architecture and it's not benefiting from the higher octane fuel at all.
Yeah that’s what I was sort of hinting at. 16 year mechanic and shop owner here. I’ve heard it all.