100 Octane Fuel - Cherokee SRT8 Forum
WK1 General Performance Discussion If you are planning on modifying your Jeep Grand Cherokee SRT8 with a performance enhancing modification, this is the section to post about it.

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post #1 of 22 (permalink) Old 03-07-2007, 06:07 AM Thread Starter
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100 Octane Fuel

Good morning

Has anyone tried using some 100+ octane fuel in the JGC? If so, was there any noticeable performance gains? I may be going to the track this weekend and am thinking about getting some if it increases performance.
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post #2 of 22 (permalink) Old 03-07-2007, 07:25 AM
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Re: 100 Octane Fuel

You will have gains. Cleaner hotter burn = More HP!

Just dont go above 100 octane You get into Leaded gas then.
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post #3 of 22 (permalink) Old 03-07-2007, 07:33 AM
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Re: 100 Octane Fuel

I am no expert, so just sharing what I have read.

With stock ECU you will get no noticeable gains as the computer is not designed to adjust up for higher octane. My understanding is that it will not hurt anything, but adding more octane to a system that already has all that it was designed for will yield nothing. This is why ECU chips come in different octane modes, because everything in the computer has been forced adjusted upwards for the higher octane. If you have a 100 octane chip and run 93 octane fuel you will do damage. But if you have a 91 octane setup and run 93 fuel you are just spending more money for octane you don't need.

The computer for safety will retard timing, etc if you put in lower than 91 fuel as part of the knock sensor, but I have just not heard anything to lead me to believe that the computer will adjust upwards.

Again, I am no expert so if I am incorrect, or if someone has proven different, then please share.
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post #4 of 22 (permalink) Old 03-07-2007, 07:39 AM
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Re: 100 Octane Fuel

You only get a benifit from using higher octane if the car calls for it or tuned for it. I actually have seen cars slow down even mine.



Quote:
Originally Posted by kramsay1234
I am no expert, so just sharing what I have read.

With stock ECU you will get no noticeable gains as the computer is not designed to adjust up for higher octane. My understanding is that it will not hurt anything, but adding more octane to a system that already has all that it was designed for will yield nothing. This is why ECU chips come in different octane modes, because everything in the computer has been forced adjusted upwards for the higher octane. If you have a 100 octane chip and run 93 octane fuel you will do damage. But if you have a 91 octane setup and run 93 fuel you are just spending more money for octane you don't need.

The computer for safety will retard timing, etc if you put in lower than 91 fuel as part of the knock sensor, but I have just not heard anything to lead me to believe that the computer will adjust upwards.

Again, I am no expert so if I am incorrect, or if someone has proven different, then please share.
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post #5 of 22 (permalink) Old 03-07-2007, 09:31 AM
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Re: 100 Octane Fuel

Hello everyone, I am new to this forum and the wonderful world of GC SRT-8's but certainly not to Mopar or high-performance vehicles. I will be purchasing my GC SRT-8 soon and have been observing this forum with great interest. FWIW my take on the 100 octane is this: Although most of what has been said is correct, I don't fully agree that it won't provide a power gain. The stock compression ratio for these engines is 10-1 that is a lot of compression for most 90-94 octane pump fuels. The addition of 100 octane unleaded fuel should provide a much higher threshold of detonation which should = less knock (however little) which will = the over zealous factory computer from pulling so much timing out. A good aggressive spark curve is paramount to building cylinder pressure (torque) and that is what these relatively heavy trucks need to get them moving. Something else to be considered is the highly oxygenated unleaded racing fuels that are becoming more and more prolific every year. I have witnessed (via engine dyno) with the addition of an unleaded/oxygenated fuel (Pro-fuel Mark II) gains of 2%-3% in torque and HP across the board. These were street engines with anything from 9.8 to 10.5 static compression. When I receive my GC SRT-8 I plan bump to compression into the 12's and run E-85 (105 octane) with all of the supporting mods of course (PCM, fuel system ) and then we'll have some crackle (think lightning) to go with the thunder. Sorry about the long first post everyone I hope someone got something out of it.
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post #6 of 22 (permalink) Old 03-07-2007, 09:48 AM
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Re: 100 Octane Fuel

Quote:
Originally Posted by RAMM
Hello everyone, I am new to this forum and the wonderful world of GC SRT-8's but certainly not to Mopar or high-performance vehicles. I will be purchasing my GC SRT-8 soon and have been observing this forum with great interest. FWIW my take on the 100 octane is this: Although most of what has been said is correct, I don't fully agree that it won't provide a power gain. The stock compression ratio for these engines is 10-1 that is a lot of compression for most 90-94 octane pump fuels. The addition of 100 octane unleaded fuel should provide a much higher threshold of detonation which should = less knock (however little) which will = the over zealous factory computer from pulling so much timing out. A good aggressive spark curve is paramount to building cylinder pressure (torque) and that is what these relatively heavy trucks need to get them moving. Something else to be considered is the highly oxygenated unleaded racing fuels that are becoming more and more prolific every year. I have witnessed (via engine dyno) with the addition of an unleaded/oxygenated fuel (Pro-fuel Mark II) gains of 2%-3% in torque and HP across the board. These were street engines with anything from 9.8 to 10.5 static compression. When I receive my GC SRT-8 I plan bump to compression into the 12's and run E-85 (105 octane) with all of the supporting mods of course (PCM, fuel system ) and then we'll have some crackle (think lightning) to go with the thunder. Sorry about the long first post everyone I hope someone got something out of it.

I agree, The reason for the chip manufactures to have a 91-93 tune is because of the bump in timing, If you didn't use the higher octane fuel with these tunes you will get detonation, and would end up frying something.

You will see some increase in power with higer octane just do to the efficacy of the burn/combustion.
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post #7 of 22 (permalink) Old 03-07-2007, 10:43 AM
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Re: 100 Octane Fuel

I tried 100 unleaded before, and I definitley felt a difference, the response was much more sudden and there was a definite increase in hp. I tried to measure it out with my gtech but it was too difficult as it was cooler out and i was having issues with traction.
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post #8 of 22 (permalink) Old 03-07-2007, 11:59 AM
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Re: 100 Octane Fuel

I am running 100 in my Jeep now and will be going on the dyno soon to compare against 93. I will post the results with no other mods done.

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post #9 of 22 (permalink) Old 03-07-2007, 12:04 PM
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Re: 100 Octane Fuel

Quote:
Originally Posted by Blown-WJ
I am running 100 in my Jeep now and will be going on the dyno soon to compare against 93. I will post the results with no other mods done.
Thats the best way to tell.

By the way - RAMM - where abouts are you in Ontario?
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post #10 of 22 (permalink) Old 03-07-2007, 12:34 PM
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Re: 100 Octane Fuel

Since "premium" pump gas here in California is only rated at 91 octane, lots of people add a 2-4 gallons of 100 octane "racing fuel" to boost the tank to the normal premium rating of 93-94. I did this all the time with my M5 and the difference was night and day. That engine would ping on 91 gas. So far I haven't heard any pinging on the Hemi with 91, which is a really good thing since 100 octane runs $9/gallon in westLA.

-Matt
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