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Thread: 89 or 91 octane towing

  1. #1

    Default 89 or 91 octane towing

    I have an 08 regular cab with 4.6 stock 3.73 axle, towing up to 6000 lbs RV. I have an edge evo that I converted to the Gryphon. Running the canned 87 tow with timing +.50 and my tire size. It is running pretty good overall.

    I know that I am kind of underpowered but for now , I am just trying to get maximum towing performance until I can get a newer F150

    I have been thinking of getting a custom tune and wondering what would be best, 89 or 91 octane tow .
    The difference in price is only about 0.03 cents per liter so cost is not a big issue.
    Last edited by bernied; 11-20-2016 at 10:24 AM.

  2. #2

    Default Re: 89 or 91 octane towing

    With a custom tune there shouldn't be much of a difference between 89 or 91. I would more worry about what is available where you are going. If 91 will for sure be available then go with that, but if you aren't 100% positive then go with 89, you can always put 91 in the tank with an engine tuned for 89, but you shouldn't put 89 in a tank with the engine tuned for 91.

  3. #3

    Default Re: 89 or 91 octane towing

    Good point, so lets say I get a 89 towing tune, I am guessing the tune would already be advanced by at least +0.50 so if I use 91 octane, would I adjust that tune to add another 0.50 on the timing or would I adjust to +1.00 . I guess what I am asking is if any modification from a custom tune is accumulative to the existing settings.

  4. #4
    JackandJanet's Avatar

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    Default Re: 89 or 91 octane towing

    Hi, bernied -

    I'm getting in on this kind of late, but I can answer your last question. If Bill writes a custom tune for 89 octane, the timing would already be advanced about 1.00 over the 87 octane tune. If you should FILL your tank with 91 octane, you should be able to advance the timing by 1.00. But, you'd really need to experiment a bit. The advance/retard settings are not "written in stone". There are other things that can effect your timing, such as your altitude above sea level, the age of your engine, carbon deposits, etc. The 0.5 advance per octane point is really only a guide.

    Hope I'm making sense here. I tried to advance the timing on my old Gryphon when I had a 2005 F150 by only 0.25 (a quarter degree). I thought I could get away with that based on my altitude (2500 ft). But, it caused an unsteady idle, so I set it back to 0.0.

    - Jack
    2014 F150 Platinum 4x4 SCrew 3.5L Ecoboost


  5. #5

    Default Re: 89 or 91 octane towing

    thanks for all the replies, I think I will be going with the 89 tow tune
    Last edited by bernied; 11-22-2016 at 11:58 AM.

  6. #6
    JackandJanet's Avatar

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    Default Re: 89 or 91 octane towing

    That's fine. One thing to keep in mind (that I should have mentioned) is that when towing, your engine is under a higher load (obviously). Bill changes the fuel mixture and shift points in towing tunes slightly to keep the engine cooler under that load and to inhibit pre-ignition. But, because of that higher load, you may not be able to advance the timing quite as much if you were to fill with 91 octane gas.

    However, since the engine is designed to run on 87 octane anyway, I don't think you would benefit that much going to 91. The higher octanes really only give you big results if you can change the compression ratio in your engine, which you can't do.

    - Jack

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