Injector size

Discussion in 'Fox 5.0 Mustang Tech' started by marine_80, Feb 22, 2012.


  1. marine_80

    marine_80 Member

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    I have a E cam notch and plan on upgrading the intake from stock to a explorer (got for $100) intake. to get the full potential out of the better flowing intake i plan on a 65mm tb and a new MAF (size?) so the question is, am i getting near the limit on the 19lbers or should i get some 24lbers and do it all at once. Also would a 4 bank chip eliminator be a good tune (from american muscle)
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  2. need4spd90

    need4spd90 Member

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    the 19's should still be fine for now
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  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Fuel injector sizing & injector photos

    Revised 11-Dec-2011 to add larger injector sizes to injector table

    Injector HP ratings: divide flow rating by.5 and multiply the result by the number of injectors. This uses a 100% duty cycle. These ratings are for naturally aspirated engines at the flywheel.

    Example:
    19/.5 = 38, 38 x 8 = 304 HP
    24/.5 = 48, 48 x 8 = 384 HP
    30/.5 = 60, 60 x 8 = 480 HP
    36/.5 = 72, 72 x 8 = 576 HP
    42/.5 = 84, 84 x 8 = 672 HP

    The preferred duty cycle is about 85% maximum, so for a safety factor multiply the final figure times .85.

    19/.5 = 38, 38 x 8 = 304 HP x .85 = 258 HP
    24/.5 = 48, 48 x 8 = 384 HP x .85 = 326 HP
    30/.5 = 60, 60 x 8 = 480 HP x .85 = 408 HP
    36/.5 = 72, 72 x 8 = 576 HP x .85 = 490 HP
    42/.5 = 84, 84 x 8 = 672 HP x .85 = 571 HP

    Remember that the above ratings are at 39 PSI. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

    See http://users.erols.com/srweiss/ to get the calculators used in these examples.

    Here's the duty cycle explanation. Duty cycle is how much of the time the intake is open the injectors are turned on. The 85% figure means that for 85% of the time the intake valve is open, the injectors are spraying. The idea is that you want some percentage of the duty cycle left over so that you have some room to grow the process.

    If you are at 100% and you need more fuel, all you can do is turn up the fuel pressure. That means the whole fuel curve from idle to WOT is affected. Maybe you are already too rich at idle, and turning up the fuel pressure makes it worse. If you had some injector duty cycle left to play with, a custom tune could use that where it is needed. That would not over richen the whole range from idle to WOT.

    If you did turn up the fuel pressure, you might be able to change the injector duty cycle to get the air/fuel mixture ratio you want since the injectors will have extra fuel delivery capability.

    With larger than stock injectors or higher that stock fuel pressure, you will need an aftermarket MAF that matches the injector size. The MAF “lies” to the computer to get a fuel delivery schedule that meets the engine’s needs and isn’t too rich or too lean. The best strategy is an aftermarket MAF and a custom tune to insure the best air/fuel ratio over all the RPM range.

    Don't forget to increase the fuel pump size when you increase injector size or significantly increase the fuel pressure



    Diagram courtesy of Tmoss & Stang&2birds
    [​IMG]

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

    Ignition switch wiring
    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    Fuel, alternator, A/C and ignition wiring
    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Vacuum diagram 89-93 Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

    HVAC vacuum diagram
    http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

    TFI module differences & pinout
    http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

    Fuse box layout
    http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif
    #3
  4. txstang84

    txstang84 Active Member

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    Is this already on a sticky?
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Not that I know of... someone else may have a similar post.
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  6. marine_80

    marine_80 Member

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    do you run 19lb injecters with your set up? i ask because you have pretty much the same set up, i ask because he have pretty much the same set up as i'm going for. And i don't know if you are still running speed density from you sig. I have a new set of bare p heads lined up as well.
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  7. marine_80

    marine_80 Member

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    don't see how it could be since i just posted it.
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  8. txstang84

    txstang84 Active Member

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    The query was directed at jrichker...many of his replies in the threads are pulled from stickys and not everyone looks for them before posting up a question.
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