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Old 03-30-2011, 03:39 PM   #1
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Anyone fueling 91 Octane?

Was on empty last night so I went to Shell to fill up and they ran out of 87 Octane so I was able to fill up 91 for the price of 87. I'm just wondering if anyone in the jeep family is fueling 89, 91 on purpose and what (if any) benefits come with fueling it.

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Old 03-30-2011, 04:18 PM   #2
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Higher octane fuel has less energy per gallon (and in some cases it can increase fuel deposits). So, don't use it if you don't need it. However, no gas is worse.

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Old 03-30-2011, 04:45 PM   #3
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The higher the octane the more power. Hence why racing vehicles use a higher octane. Plus you will usually get a little better fuel economy, and there is less ethanol in a higher octane which make fuel economy shit and draws water into ur gas.
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Old 03-30-2011, 04:59 PM   #4
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Quote:
Originally Posted by markg018 View Post
The higher the octane the more power. Hence why racing vehicles use a higher octane. Plus you will usually get a little better fuel economy, and there is less ethanol in a higher octane which make fuel economy shit and draws water into ur gas.
This is a myth. The best gas for your JK is what's recommended in the owners manual. I'm assuming 87 octane, like the TJ. The only thing higher octane will help is with engine pinging. If your engine isn't pinging on 87 and you put in premium you're wasting your money.
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Old 03-30-2011, 05:04 PM   #5
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Quote:
Originally Posted by markg018 View Post
The higher the octane the more power. Hence why racing vehicles use a higher octane. Plus you will usually get a little better fuel economy, and there is less ethanol in a higher octane which make fuel economy shit and draws water into ur gas.
not true. higher octane fuel just takes more to ignite. if the engine is pulling the same amount of oxygen, the fuel/air ratio doesn't change a bit, and there is no increase in power. jeeps should run 87 octane, but as said, 91 is better than none.


this is just what ive learned from like.. science class haha. not a fuel expert or anything
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Old 03-30-2011, 05:19 PM   #6
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I been running on 93 for nearly a year but I'm modified to reap it's rewards

The stock 3.8 is designed for 87. The higher octane stuff won't hurt you. Over time though it might carb up your engine a bit.

Due to the stock compression you won't burn 91 or 93 totally, and you'll blow it out the tail pipe. Octane basically is like fuel's detonation number. Your compression is set for 87 stock, so run that. If you aren't Super Charged or Chipped, you're wasting money running higher than 87.

But no, 91 or 93 isn't going to hurt your Jeep in the short term, or anything major in the long-run. Just a waste of $$$
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Old 03-30-2011, 05:23 PM   #7
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I use it with the Superchip 91 tune, my Jeep runs great
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Old 03-30-2011, 06:26 PM   #8
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I use 89 ethanol because its cheaper. Normally I never used ethanol in anything I had because I normally get fairly poor mileage when using it, especially in the winter months.
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Old 03-30-2011, 07:39 PM   #9
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Quote:
Originally Posted by FenderBender
Was on empty last night so I went to Shell to fill up and they ran out of 87 Octane so I was able to fill up 91 for the price of 87. I'm just wondering if anyone in the jeep family is fueling 89, 91 on purpose and what (if any) benefits come with fueling it.
Only the uneducated..... It's burning cash.
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Old 03-30-2011, 08:32 PM   #10
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Originally Posted by BLEGAN

not true. higher octane fuel just takes more to ignite. if the engine is pulling the same amount of oxygen, the fuel/air ratio doesn't change a bit, and there is no increase in power. jeeps should run 87 octane, but as said, 91 is better than none.

this is just what ive learned from like.. science class haha. not a fuel expert or anything

higher octanes ignite easier, burn hotter. I'm not saying to run anything but 87 that's wut the engine is designed for. Because a higher octanes burn hotter this will create carbon buildup as time passes because the engine is not able to get rid of the excess carbon after it burns
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Old 03-30-2011, 08:38 PM   #11
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I tried the 87 oct tune on my superchip & it was nowhere as peppy as the 91, so 91 it is
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Old 03-30-2011, 08:51 PM   #12
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Speaking of the superchips. Did you try 87 tune before going to 91 and how much difference did you notice.

Why I asked, is I had a gascap error and since I was due for a oil change too, I took it to the dealer today so I took the 87 tune off and went back to stock. In driving it today back to stock I really didn't notice a difference then yesterday at 87 tune. Just wondering if going to 91 tune if it will make a more noticeable difference?

By the way, going beck to stock reset the gascap error message even when clearing codes didn't. Not sure why I got the gascap error in 87 tune and not in stock.
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Old 03-30-2011, 08:51 PM   #13
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Quote:
Originally Posted by markg018 View Post
higher octanes ignite easier, burn hotter. I'm not saying to run anything but 87 that's wut the engine is designed for. Because a higher octanes burn hotter this will create carbon buildup as time passes because the engine is not able to get rid of the excess carbon after it burns
This is still a myth. You have it backwards. The lower the octane #, the quicker the fuel ignites.

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Old 03-30-2011, 08:56 PM   #14
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I tried running 91 octane gasoline with the Superchips 91 octane tune for about a month or so, and didn't notice any change in performance or mpg's compared to 87 octane gasoline with the Superchips 87 octane tune, so I went back to 87.
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Old 03-30-2011, 09:42 PM   #15
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Quote:
Originally Posted by jcf
I tried the 98 oct tune on my superchip & it was nowhere as peppy as the 91, so 91 it is
You have a 98 tune?

I'm running 93. Started on 87. After a few months I tried out 93, jumping over 91. I noticed a difference between 87 vs 93, so I stayed tuned for 93. No pings or anything for nearly 50 tanks or so of it. It seems to have more down low. I can burn-out 35's Enough for smoke. The 87 would chirp the tires.
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Old 03-30-2011, 09:45 PM   #16
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Pokey has it right. Typically, higher compression engines need higher octane so that they do not pre-detonate, I.e. "ping". If you don't have pinging you don't need higher octane.

Cetane in diesel fuels, on the other hand is an indicator of energy/resultant power, and when shopping around for diesel fuel you will notice better performance from higher cetane fuels. But with octane in gas... Nada.
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Old 03-31-2011, 02:41 PM   #17
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Enjoy it while you can. It won't be long until were burning COAL !!! JEEPS will run on almost anything...
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Old 03-31-2011, 10:51 PM   #18
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Read your manual, like mine I'm sure it says to use 87. Don't use anything higher cause over time it can do more harm than good. 87 is the recommend octane.
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Old 04-01-2011, 01:21 PM   #19
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Originally Posted by markg018 View Post
The higher the octane the more power. Hence why racing vehicles use a higher octane. Plus you will usually get a little better fuel economy, and there is less ethanol in a higher octane which make fuel economy shit and draws water into ur gas.

87 Octane Gasoline: 34.8 MJ/liter 44.4 MJ/kg 125,000 BTU/US gal

95 Octane Gasoline: 33.1 MJ/liter 43.5 MJ/kg 122,500 BTU/US gal

Today's gasoline is not your father's gasoline.

Displaced hydrogen and carbon (energy) due to increased additives by volume in higher octane fuels is fundamental to gasoline energy content. The difference in energy content today is related to the fuel additive package that can be added to gasoline for controlled burn (most oxygenates added for controlled burn are alcohols and by volume they reduce energy). So, oxygen and other compounds added for cleaning do not contribute energy. Consequently the fuel has less energy content. For the same efficiency and power output, more fuel has to be burnt. The slight improvement in combustion efficiency that oxygenates might provide does not completely compensate for the added oxygen volume.

Engines that use higher octane fuels make more power due to higher compression and cam timing, not the higher octane.

Manufacturers also increase octane today by blending in additional Ethanol (reformulated gasoline), which again slightly lowers its energy content). 10% Ethanol reduces energy by 3%
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Old 04-01-2011, 07:07 PM   #20
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This is a good debate. Jeep 3.8L calls for 87 so that's what you should use. A benefit to higher octane gas (Shell anyway) is that in Canada the Gold product has got much more of the engine cleaner additive package and contains no ethanol (which changes the energy content). Making octane in a refinery is usually difficult and more expensive as the fuel is processed through a unit utilizing platinum catalyst (typically called a "Platformer") so the extra cost is real.

Rule of thumb is that you can go 1 less octane number - RON - for every 1000' of altitude for a normally aspirated engine. I had a '72 Plymouth that would work on 87 fine in Calgary - 3500' elevation - and ping every chance it got on 87 in Vancouver at sea level...91 octane in Van solved that.

Having said that I filled Premium 15x in a row and now I'm on my 20th tank of Regular. No change in fuel mileage or performance in any way that I can see.
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Old 04-01-2011, 07:47 PM   #21
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Originally Posted by MMJ89586
I use 89 ethanol because its cheaper. Normally I never used ethanol in anything I had because I normally get fairly poor mileage when using it, especially in the winter months.
Your burning ethanol in your Jeep? I didn't think they were designed for that.
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Old 04-02-2011, 01:33 PM   #22
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You will get the best performance using the lowest grade of octane without knocking. Anyone who buys higher octane gas because the number is higher so it must work better is throwing money away. The engines that gain benefits from higher octane run higher compression ratios and are built do do such.
Octane is nothing more than knocking resistance. Lower octane ratings can combust at much lower compression ratios spontaneously. Where as higher octane ratings can take much higher compression before igniting spontaneously. Fuel igniting due to compression and not spark is knocking, and knocking is bad.
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Old 04-02-2011, 01:34 PM   #23
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Old 04-02-2011, 04:47 PM   #24
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I run a tank of 89 about once a month, and I can tell the difference in mileage. I get a little better mileage on the tank of 89. But most of the time I stick with 87, saves more in the wallet....
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Old 08-22-2012, 02:57 PM   #25
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Okay -so what happens if your engine IS pinging with 87 octane? I put in an fuel injector detergent and filled the tank with 91 octane and the pinging stopped and I got 2 mpg better mileage - but that's short term.
The question is - what made my 3.8L engine start pinging after 25,000 miles?
I've heard that ethanol is the culprit - but I haven't heard of any cure.
Any advice?
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Old 08-22-2012, 05:29 PM   #26
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08/01/2012 using 87. manual 3.10 gears, stock steelies
never exceeded 3k rpm
no a/c at all
310.2 miles
dte 65

08/15/2012 using 89.
redlined to 6k twice
used a/c all day everyday
312.1
dte 60

its about the same.
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Old 08-22-2012, 06:18 PM   #27
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F the owners manual. seriously

my experience;
most 87 -pinging and knocking
Exxon93 -no ping world of difference
sunoco 89 -pinging after two tanks
sunoco 87 -pinging and knocking
Exxon93 -no ping world of difference

running high test from here on out. octane = anti knock. period. my 10:2:1 engine preforms best with high test. FACT



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Old 08-22-2012, 06:22 PM   #28
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Quote:
Originally Posted by JKWrangler2012
F the owners manual. seriously

my experience;
most 87 -pinging and knocking
Exxon93 -no ping world of difference
sunoco 89 -pinging after two tanks
sunoco 87 -pinging and knocking
Exxon93 -no ping world of difference

running high test from here on out. octane = anti knock. period. my 10:2:1 engine preforms best with high test. FACT

Shell 93 = no ping.

I am tuned for 93 but if I use crap gas, it will still knock.
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Old 08-22-2012, 06:48 PM   #29
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A gold star to everyone who said higher octane is harder to ignite. Higher octane fuels let you run higher compression ratios, superchargers and turbo chargers which also result in higher compression ratios, spark timing closer to TDC for each piston stroke, and more ideal fuel/air ratios WITHOUT the engine turning itself into a diesel and pre-igniting which will usually destroy an engine very quickly.

This used to be accomplished by adding Tetra-ethyl lead to the fuel - ever heard the term "Ethyl" for premium? That's where it came from. The lead did two things increased the octane (inhibited ignition) and lubricated the valves and valve seats. Oh yeah, it two other things: poisoned platinum based catalytic converters and added a lot of lead to the environment. Both of these things were bad so we got unleaded gasoline. The new octane enhancer was MTBE but it was found to be not very good for the environment especially the groundwater so it was outlawed and the government mandated that Ethanol be used as the octane enhancer and oxygenator. Ethanol does both of these things very well but not without some costs. It contains less energy, is very hard on gaskets and seals and it attracts and hold water very strongly. The reason it is used in race cars is so that they can run ridiculously high compression ratios and thus they can spray a lot more fuel into the cylinder per cycle but it contains less energy per ounce of fuel sprayed into the cylinder. To solve the gasket problem and the water problem (the two are related in certain ways) additives have to be used and care has to be taken to insure no water gets into the fuel and that includes water vapor from the air. Gaskets have to be redesigned to handle the ethanol so do not use anything that has more than 10% ethanol unless you have a vehicle designed for E85 fuel.

Hope this helps.
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Old 08-22-2012, 06:56 PM   #30
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So what does a chip do with a different octane tune? If higher octane prevents preignition from high pressure or heat, does it change the timing of the spark? Why would that require a different octane rating?

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