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Thread: E85 injector sizing

  1. #1

    E85 injector sizing

    I'm switching to E85, looking at the stoich ratios I don't understand why most forums I search in are coming up with 30% more injector. Doing the math I come up with 46.7% more fuel needed to go from 14.7 to 9.7 can anyone explain this?

  2. #2
    Tuning Addict 5FDP's Avatar
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    9.7 is just a stoich value of the fuel, not the actual change for the fuel requirements. Unless you get it from a barrel, it's never truly E85 at the pump and thus the want for a flex fuel sensor.

    Regular gasoline is stoich of 14.7, E10 would be 14.1ish and it just continues going down as the alcohol content rises.

    The 30% guesstimate is still pretty accurate as far as fuel needs are concerned. There are many injectors calculators you can use to help size your injectors.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Quote Originally Posted by 5FDP View Post
    9.7 is just a stoich value of the fuel, not the actual change for the fuel requirements. Unless you get it from a barrel, it's never truly E85 at the pump and thus the want for a flex fuel sensor.

    Regular gasoline is stoich of 14.7, E10 would be 14.1ish and it just continues going down as the alcohol content rises.

    The 30% guesstimate is still pretty accurate as far as fuel needs are concerned. There are many injectors calculators you can use to help size your injectors.
    Thank you for the response. I'm aware that the fuel percentages aren't consistent. The thing is I've found a few injector calculators that use 47% and some that give a general 30% increase. It's quite a bit of difference. Using the ratios the math is no doubt 46.7% going from gasoline to E85. The reduction from E85 to gasoline would be 32%, but I find it hard to believe so many people are using that number arbitrarily. I was thinking maybe the mixture doesn't need to be as rich with E85 under load/boost and that's where the difference is. But I'd like to hear an advanced tuner jump in so I understand before buying injectors.

  4. #4
    Tuning Addict 5FDP's Avatar
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    I run leaner with E85 in my truck. Roughly .85 lambda (12.5afr)with pump 89 octane and .88 to .89 lambda (13.0afr) with E85 (which is roughly 60-70% at the pump).

    With boost you can do the same thing, in AFR terms here, instead of 11.0 you can be closer to ~12.0 at moderate boost levels.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.