fuel injector mass air question

Discussion in 'Fox 5.0 Mustang Tech' started by mustang 88, Apr 6, 2013.

  1. mustang 88

    mustang 88 Member

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    what will happen if I install my 24 lb injectors in motor with my 19 lb mass air sensor? This will be very temporary but I'm itching to get them installed. I tried to find a similar post with no luck Thanks alot.
     
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  2. f8tlfiveo

    f8tlfiveo My wife likes my spool and blow-off valve.

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    Not going to work too well, if it works its gonna run like crap. Just get the right stuff. Plus there will be no power gain putting 24lb injectors in. In my opinion 24lb injectors are a waste. Bigger injectors are there to support your fuel needs when you have parts that will make more power and need more fuel.
     
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  3. mustang 88

    mustang 88 Member

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    ok thanks I thought so but you never know . Do you think my combo needs 24 lb injector 80 mm mass air cold induction, 75mm throttle body,gasket matched fully ported and polished upper and lower gt-40 intake, gt-40 heads also ported and gasket matched,long tube headers,msd6al box, e-303 cam, under drive pulley,and electric fans.
     
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  4. f8tlfiveo

    f8tlfiveo My wife likes my spool and blow-off valve.

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    I ran about the same thing for 2 years on the 19lbers. The duty cycle of the injectors is prob at its limit with those mods. If you already have the 24lb injectors and can find a mass air meter cheap I would swap them over. I would have went for 30lb injectors to start with, but since you have the 24's they would give you a little extra breathing room. I will be using 60lb injectors on mine with a hpx slot meter when I put my turbo on. But I also can get around the "calibrated" Maf with the tuning equipment on the car. This is the best way to do it in my opinion, but if you are on a budget the calibrated Maf will be ok.
     
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  5. jrichker

    jrichker StangNet's favorite TOOL
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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/#jcalc 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
     
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