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Thread: E85 blend with 87 octane

  1. #1
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    E85 blend with 87 octane

    I've got a '16 Silverado 1500 4wd L86/8L90.

    So there's a low octane table and a high octane table. If I understand it correctly, excessive knock count causes the timing table to drop down to low octane, right? But how does it know when to revert back to the high octane table? Does it revert after a fill-up? Random timing test to see if it knocks?

    I ask because I simply don't want to pay for 93 octane. It's usually 50-60 cents more/gallon and that means I'd spend about $60 extra/month. My thoughts are to blend in some E85, which is even cheaper than generic 87 around here. 8 gallons of E85 and 18 gallons of E10 87 would yield approximately 91 octane (assuming 100 octane E85) and 33% ethanol.

    Without having a FF sensor and tuning adjusted, shouldn't the fuel trims adjust on their own? I realize the full potential wouldn't be met until timing is adjusted properly, but since the knock capacity has been increased wouldn't it be running higher timing than on 87 alone?

    Thanks in advance!

  2. #2
    Tuning Addict 5FDP's Avatar
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    It uses the knock learn factor. If there is a lot of knock the knock learn factor will be in play to interpolate the timing between the two tables and over time it will slowly go back to just the high octane table if no knock is detected.

    The harness for the flex fuel sensor is already in the truck. It's on the rear cross member after the transmission, it's a red-ish/brown plug with a dummy end stuck in it. You can buy a $25-30 flex fuel sensor and plumb it into the fuel system right at the fuel tank. I have about $50 total in my flex fuel addition with the sensor and some fittings/hose to make it work.

    If you have a crew cab truck the harness needs to be extended about 2-3 feet to reach the fuel tank. Double cabs may need some length added too but that is easy. I wouldn't want the fuel trims to try and fix anything if you are running E30 or higher, just install the sensor.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
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    Knock learn factor - got it! That's awesome.

    I've got a few threads bookmarked from other forums about the process and it looks super simple even for a CC truck. The only thing holding me back is that I have 27,000 miles of powertrain warranty left...

  4. #4
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    E30 or less then, so I'll try to keep less than 6 gallons in the tank until I get the sensor and tune done. At an effective octane rating of 89-90, would a E25-E30 blend have an detonation resistance similar to 91, or even 93, E10 gasoline?

  5. #5
    There is a video I can post that was done by pmoore4321 on how to do it. In his original video he used russell fittings then changed it to DSX fittings.

    Don't use the Russell fittings after two years I just had mine fail and shower the ground with 40 psi of fuel. They lasted two years before it failed. Spend the 50 buck on the DSX fitting or there is a way to use a bent OEM extension fitting.

  6. #6
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    Quote Originally Posted by Jonblarc7 View Post
    There is a video I can post that was done by pmoore4321 on how to do it. In his original video he used russell fittings then changed it to DSX fittings.

    Don't use the Russell fittings after two years I just had mine fail and shower the ground with 40 psi of fuel. They lasted two years before it failed. Spend the 50 buck on the DSX fitting or there is a way to use a bent OEM extension fitting.
    Thanks for the heads up! I think I've actually seen his two videos. Good feedback on the fittings. There's one (CJ Tunes) that installs right on the hard line. I've done some work on fuel lines with a flare tool in the past and it's worked great so I wonder if that's a better option.

  7. #7
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    Another thought here. If the O2's can reasonably accommodate for E30 under closed loop, then under WOT /open loop, I think I'd be pretty much spot on. I've seen several references to these Gen V motors running pig rich above 3500 RPM somewhere in the 10.5-11.5 range. If my calcs are correct, E30 power stoich should be right in that range!

  8. #8
    This will be the way I probably go when I decide to fix it next week. And use the bent fuel line.

    https://www.gm-trucks.com/forums/top...ge/3/#comments

  9. #9
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    That's a great setup @jonblarc7 ! thanks for sharing!

  10. #10
    Quote Originally Posted by lucas287 View Post
    That's a great setup @jonblarc7 ! thanks for sharing!
    I just want to let you know I got that fuel line hooked up and when for a log and it didn't go well at all. So log yours before you beat on it to much. The turns in the line are making to much of a bottle neck at wide open throttle.

    My fueling has been around .85 to maybe .87 in spot during WOT pulls. I installed the line last night but didn't go for a drive. This morning I hook up the laptop to log it this morning. WOT on the wideband was .95 not good. But at idle and cursing the fuel was fine.

    So at lunch I crawled under the truck and unhooked the sensor and the new fuel line and went for a drive. Fueling returned back to normal with no other adjustment. Thanks God I didn't go ahead a fuel up with E85.