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Thread: Switching Injectors

  1. #1

    Default Switching Injectors

    I'm going to be switching my car to E85. My current injectors are Holley 66 lb/hr. I'm switching to 120s. I've got a whole tank of gas to run out of the car. Will it compensate on its own when I change the injector size in the ECU, or does the Base Fuel Table have to be reworked? My thought is that the computer knowing the injector size and the required pound per hour requirements of the engine, would make the change.
    Thanks, Russ

  2. #2
    Join Date
    Nov 2013
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    Chicago IL
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    Default

    Well normally, the beauty of a lb/hr value in the fuel table is that (if you stay on the same fuel) when you change injectors, all you have to do is change the fuel injector values and it will work. But because you're switching to a different fuel (E85) you will also have to change the fuel tables as well.

    The easiest way to do this is to change the Target A/F table to read E85 values (as well as the fuel type in the system parameters).
    Then let the fuel table change on its own when it asks if you would like it to change the fuel values for you, just say yes.

    You can multiply the target A/F table by 0.67. Then you can multiply your Cranking Fuel & Acceleration Enrichment lb/hr tables by 1.49. Figure that you will probably need a few degrees of spark here & there, and everywhere as well when you switch to E85, but that's up to you to determine how much and where you need it.

    If you plan on going back & forth between two fuels from time to time (and I suggest you occasionally run some regular unleaded pump gas through the system once in a while to clean out the system, and to prevent corrosion issues that happen with ethanol fuels), you can make an Advanced Table and use the Fuel Flow Multiplier. This will change all the fuel tables in one nice swoop, but will leave the Target A/F Table still reading on the gasoline scale. It will also allow more flexibility for when the E85 only tests at E70. Just put in the new multiplier, and you are good to go. 1.49 for E85, 1.37 for E70, 1.0 for when you want to run non ethanol gasoline.
    Last edited by S2H; 08-15-2016 at 09:27 PM.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  3. #3
    Join Date
    Nov 2013
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    Chicago IL
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    Default

    This table should help:
    Ethanol % AFR Multiplier Divider
    0 14.70 1.00 1.00
    5 14.42 1.02 0.98
    10 14.13 1.04 0.96
    15 13.85 1.06 0.94
    20 13.56 1.08 0.92
    25 13.28 1.11 0.90
    30 12.99 1.13 0.88
    35 12.71 1.16 0.86
    40 12.42 1.18 0.84
    45 12.14 1.21 0.83
    50 11.85 1.24 0.81
    55 11.57 1.27 0.79
    60 11.28 1.30 0.77
    65 11.00 1.34 0.75
    70 10.72 1.37 0.73
    75 10.43 1.41 0.71
    80 10.15 1.45 0.69
    85 9.86 1.49 0.67
    90 9.58 1.53 0.65
    95 9.29 1.58 0.63
    100 9.01 1.63 0.61
    Last edited by S2H; 08-15-2016 at 09:32 PM.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  4. #4

    Default

    Thanks, I thought it worked that way. What fuel pressure do you recommend with E85? My tuner is recommending 60-65 psi static, no rise at rate. I'm running about 13 pounds of boost, and the car makes a tick over 700 RWHP on pump gas. Should be over 800 with E85.

  5. #5
    Join Date
    Nov 2013
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    Chicago IL
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    I think you should get a new tuner if he is suggesting a static fuel pressure with boost. In general, for boost, you ALWAYS want a 1:1 boost reference regulator that increases fuel pressure with boost. You need something that counteracts the boost that is pushing up against the injectors.

    We try to run a lower fuel pressure with a Larger injector. Makes controlling the pulsewidth at idle better. The problem is, as you go up in pressure, you lose total flow (they are inverse of each other), so the higher you go in pressure, the less total flow you get. Which means in reality, you are losing fuel system capacity. You do increase Injector Rating when you increase your base fuel pressure, but its only useful if you have more than enough pump to keep up with the flow demand.

    A good example is the Holley 12-1800 pump, which flows *200 GPH at 6 psi*. But at 43 psi, it only flows 156 GPH, which is a considerable drop in flow.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  6. #6

    Default

    As you can see, there is inverse relationship between Fuel Pressure, Injector Flow & Fuel Pump flow. As fuel pressure rises, injector flow increases & fuel pump flow decreases. By doing some calculations, you can find the fuel pressure where injector flow & fuel pump flow intersect. This will give you the greatest fuel volume out for your current system. In my case, running dual Walbro 450 LPH pumps & Holley 120lb injectors, that point is around 68 psi where flow is around 700 LPH.

    Scott, how does this work with a boosted application? With a 1:1 regulator, the pressure differential across the injector should remain constant, correct? So as you increase fuel pressure at the pump, due to boost, your pump flow will decrease, but you will not be getting a corresponding increase in injector flow, right? So in my case at 58 psi, the injectors flow the same as the pump flows at 78 psi, so if I was running 20 lbs of boost, 58 psi would be my optimum base fuel pressure for my current system. Thoughts? Mike

    EDIT: Here's the spreadsheet I used for my calculations. I found it on another forum:
    https://www.dropbox.com/s/mitiuu85cg...ow_v4.xls?dl=0
    Last edited by silverbullet9; 08-25-2016 at 01:54 PM.
    1967 Camaro. 5.3L L33 swap, Holley Dominator EFI. 10.65 @ 128 so far.
    Rick's Tank with dual Walbro 450s, Holley 120 lb/hr injectors.
    LS1 intake, stock DBW TB, LJMS custom cam/BTR springs/Tick pushrods.
    TH400, FTI Converter, Fab9, 3.25 gears/Wave-Loc diff, 275/60/15 M/T ET Streets. 125 HP dry nitrous.
    Waiting to install Holley Turbo Manifold Kit: Forced Inductions Billet S485/Vibrant 18x12x6" A2A. Looking to go 8s this year.

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