90 Octane with Super Charger

Discussion in '80-Series Tech' started by aktundra, Feb 20, 2009.

  1. aktundra

    aktundra

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    not sure if this is related,

    https://forum.ih8mud.com/80-series-tech/268894-330-cel-code.html

    but I have been meaning to throw out this question.

    Seems like the SC kit instructions say to run 92 octane premium. I didn't really investigate what was available until after installing the kit, and I have only been able to find 90 octane around town.

    Are the folks with a SC able to find 92 octane or are you running 90 octane ?
     
  2. Atoyot1031

    Atoyot1031

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    I run 91 as that is premium around here, but my buddy, mountjoy_99 runs 89 octane (midgrade). Both rigs are SC'd.
     
  3. jeepocabra

    jeepocabra

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    The higher your altitude the lower octane you can safely run. i.e. a car that says run 91 octane normally is rated for that at sea level where there is more oxegen. Up in the high land you can get away with 85 because of the lower oxegen levels the altitude affords. Do it all the time here in Idaho with cars, have yet to run into a problem.

    Also there are multiple ways of rating octane so the number can differ due that that too. The SC instructions will state what rating they use to get the 92 rating.

    Not that any of the above helps you with your question. I would say that 90 is more than likely ok for you. However I do not own a SC landcruiser (3FE of fury for me) so take my advice with a large grain of salt.
     
    Last edited: Feb 20, 2009
  4. SUMOTOY

    SUMOTOY

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    I've run all grades (87,89,92) in my SC truck in the midwest without issue for the last 80k. We have 93 available in Chicago, but on my forays to NE and CO, 91 is the top flavor. No issues.

    The knock sensor will massively retard the timing if there is an issue, and you will know it. IME, the 87 runs fine, but the difference in power (drop) is noticeable, and the higher octane tends to give better mileage, so I don't think there is a real cost savings.

    HTH

    Scott J
    94 FZJ80 Supercharged
     
  5. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    My experience:

    Sea level available premium octane 93

    ~4000 foot available premium octane 91

    ~6500 foot available premium octane 90

    As altitude increases octane requirement drops.

    This is only a problem when you are traveling down hill. The good news is that 80s burn gas so fast that most of the lower stuff is gone by the time you get to the lower altitude.....
     
  6. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    Wow.

    You are the only guy on the planet with a 93-94 that does not have a knock issue at WOT without some sort of fuel enrichment/octane boost.

    How is that possible?
     
  7. Atoyot1031

    Atoyot1031

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    Most likely magic...
     
  8. jeepocabra

    jeepocabra

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    Uhmmm power goes up as octane goes down. Octane is a measure of how "fast" fuel burns. More refinement = higher octane= less energy per fuel amount. It a common misconception that higher octane gives more power as it is run in higher performance motors, because these motors have a higher compression ratio. However, you may get less power as the computer in the LC retards the timing to avoid knock.
     
  9. Michael Hanson

    Michael Hanson

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    We used to go to the airport to fill up our Mustang Cobra.We could get 120 plus. It made for a good ride. Mike
     
  10. SUMOTOY

    SUMOTOY

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    I have no disagreement with that summary, and that's how I understand octane works as well - but your conclusion that "power goes up" reducing octane is not correct. Combustion energy potential goes up, but that doesn't mean 'power' goes up. I claim the power and efficiency of the engine is down because (higher octane = more timing advance possible <>) lower octane = less timing advance possible, and results in a noticeable difference in reduced engine power. I understand and believe that is due to how knock vs octane and fuel tabling works in ECU programming.

    I run the stock boost, stock tire size/weight and darn close to the stock truck weight. Quite possible one of the only SC guys on this forum to do so? I don't think there is any magic, I do it quite often. IME with high performance FI engines, it's quite possible to run lower octane fuels. IME with program tables in knock sensor motors, it's quite easy to see and feel the "regular" fuel tables, or timing retard performance differences.

    I've run the tanks of 87 fuels back to back with 93, and the performance difference is noticeable. And BTW, when I was on the way/at Steamboat Spring CO Ice Track 2 weeks ago, 91 Octane was available at all altitudes above 6500ft, including all downtown stations at 6700ft. IIRC, octane fuel availability is a state mandate, not an altitude mandate in the US.

    My point to the OP, is that 90 octane will not harm the SC if that's the highest octane available. He would notice a difference in performance running 93 in the midwest, that doesn't mean he needs 'octane' boost using the highest grade fuel he has available.

    Scott J
    94 FZJ80 Supercharged
     
    Last edited: Feb 21, 2009
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