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New GT500 owner - Any potential issues running 95 octane mix on a 93 tune?

Discussion in 'SVT Shelby GT500' started by lfgt, Sep 5, 2019.

  1. lfgt

    lfgt New Member Established Member

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    I have just recently purchased a modified 2007 gt500 that is tuned for 93. Makes around 650 rwhp on 16.5 lbs of boost through the stock exhaust manifolds and cat-less H-pipe (Other mods in sig). Unfortunately from my location the closest top tier station with 93 is 40 miles away. Fortunately there is a Harley dealership within 2 miles that has 91, 95, and 100 on pump that is managed by their service department. The 95 is a mix of the 100 (Sunoco 260 GT) with the straight 91. I am planning on running this until I come up with a better solution. I was able to contact the company that previously tuned the car and they thought it would be fine running the 95 as long as the mix is consistent but still suggested I get on a dyno to verify the A/F ratio and to check the timing marks on the spark plugs.

    So my question is has anyone else run into issues running a race gas mix when the car was not tuned on it? Or does anyone see any potential issues?

    I will have it on a dyno in two weeks to verify the A/F ratio. I do not think I am going to bother pulling and checking plugs. The plugs in it probably have less than 1000 miles on them. I realize that a new tune would better utilize the higher octane and gain more power but making more power is not a priority.
     
  2. HKusp

    HKusp Member Established Member

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    I am not an expert, far from it. That being said, if the mix is just fairly consistent, and you are at at least 93 octane, logically I can't see where there would be any problem running it.
     
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  3. Bearbo

    Bearbo Well-Known Member Premium Member Established Member

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    No problem. Should run even smoother. On the plus side, you get to hang with the cool guys at the Harley dealer.
     
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  4. decipha

    decipha Active Member Established Member

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    the biggest problem with race fuels is the stoich changes so it can cause lean out or enrichment

    you can reference the stoich value here Fuel / EFIDynoTuning

    which gives you about a 14.0 stoich similar to e10 so it will be fine
     
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  5. lfgt

    lfgt New Member Established Member

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    Thanks for the replies.

    Maybe I am looking to far into this but it surprised me the tuner suggested swapping in some new plugs and doing some pulls to verify timing marks on the spark plug straps which seems excessive for just running different/better fuel.

    The Sunoco 260 GT has E10 and a stoich of around 14.0 and when mixed with straight 91 (Stoich of 14.64) should bring the ethanol down to around 5% or below and a stoich value of around 14.3 to 14.4 So maybe I will run a little rich? Not enough to be concerned about?
     
  6. 69b302

    69b302 Active Member Established Member

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    You will not hurt anything running a higher octane, but should be tuned for the fuel you use. More octane means slower burn, so you could see it slightly richer, or give it some more timing to take advantage of the longer burn.
     
    Last edited: Sep 6, 2019
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  7. lexustech48

    lexustech48 RIP FoMoCo 1903-2014 Premium Member Established Member

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    O2 sensors should be able to compensate for that
     
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  8. biminiLX

    biminiLX never stock Established Member

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    Should be no problem at all. It’s a great option. Hell, if you datalog I’d give it 1-2 degrees above 5000rpm and ride out. Pump 95 would be sweet option.
    -J
     
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  9. nxhappy

    nxhappy Vette Killer Established Member

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    Torco.
     
  10. lfgt

    lfgt New Member Established Member

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    I figured a stoich of around 14.3 to 14.4 with this mix since the 91 used has no ethanol. Making it run on the rich side. The breakdown for 10 gallons of 95 is 5.6 gallons of 91 and 4.4 gallons of 100 using a octane calculator. Close to a 50/50 mix which brings total ethanol down to just under 5%.

    I wish they would. The O2's are not wide-bands for 2007-2009 (I think 2010 also). I was told their only purpose is to make sure the cats are functioning. Since I do not have cats and there is no check engine light they must be turned off in the tune.

    Eventually I will get a tune specifically for this mix. The 95 is a sweet option except for the price $6.25/gal
     
  11. biminiLX

    biminiLX never stock Established Member

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    I think you can buy VP X85 for $7/gallon on less.
    All depends on how much you drive your car and what fuel is available.
    Can you datalog? How is the car tuned?
    If you run 95 and have SCT, you should be able to add 2deg timing over 5000rpm and get your moneys worth from the cost of 95, otherwise you’re burning extra octane/cost with little benefit.
    -J
     
  12. lexustech48

    lexustech48 RIP FoMoCo 1903-2014 Premium Member Established Member

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    Incorrect. You have 2 sets of o2 sensors on your car from the factory. 1st set is the primary o2 sensors. Your car wouldnt run correctly at all without these sensors. You are correct that on 07-10 they were not wideband. HOWEVER, you still have them and their job is STILL to monitor and report exhaust o2 levels in closed loop to the computer. Its less accurate than the Widebands, but its still more than enough to determine between straight gas/racegas and e10 pump fuel. Now, if you were trying to run E85, yes, you'd need to upgrade the system to a wideband.

    Your secondary o2s are probably shut off for "off road use only". Those are the sensors that monitor catalyst efficiency. SOME manufacturers use them for A/F fine tuning, but i do not believe Ford factory calibrations ever did for GT500.
     
  13. Catmonkey

    Catmonkey I Void Warranties! Premium Member Established Member

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    Make sure it's unleaded. It should be, but your O2 sensors won't live long if its not. If you still have cats, neither will they.
     
  14. lfgt

    lfgt New Member Established Member

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    It came with a SCT X4 and I have 0 experience using it. I will need to do a lot of research before I feel comfortable modifying the tune myself. I am Ok with wasting extra octane at the moment.

    Thanks for the info I was unaware of this. I guess I won't worry about the minor differences of ethanol and stoich numbers.
     
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  15. lfgt

    lfgt New Member Established Member

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    I am thinking I will just get in the routine of making the 50 mile trip for pump 93 and bring back a months worth of gas and just store it in the garage. Then just run the 95 if in a pinch.

    The only top tier stations I have access to that carry 93 are Phillips 66 and Sinclair. Neither are usually recommended by tuners so for peace of mind and insurance I will mix 1 gallon of 100 to every 6 gallons of 93 to bring the octane up to 94.

    Has anybody had bad luck with gas from Phillips 66?
     

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