im buying new mass air & fuel injectors! 24 or 30?

Discussion in 'Fox 5.0 Mustang Tech' started by staticc, Dec 22, 2003.


  1. staticc

    staticc Founding Member

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    i plan on doing my 302 over completely. H/I/C (well i already have HIC.. but better matched:)) with most likely nitrous in a few months.
    so id expect probably uh. ~420hp with nitrous?...

    is 24lb injectors enough for that? or not enough?
    or should i just bump it up to 30lb'ers now
    #1
  2. DirtyD916

    DirtyD916 Active Member

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    if you plan on staying with your setup then 24 however if you go supercharged or larger displacement then the 30's will give you plenty of room to grow. :flag:
    #2
  3. staticc

    staticc Founding Member

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    i highly doubt id ever bore out the block, or put on a supercharger. supercharger is just way too much $$$$

    lets just keep it a 302 :D
    .. but i plan on swapping H/I/C later for better matched stuff. and getting every bolt on made
    #3
  4. mike keirstead

    mike keirstead New Member

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    If u are using Nitrous then definatly go with the 30s
    #4
  5. joncash

    joncash Founding Member

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    If you use a wet nitrous kit, the fuel enrichment will be part of the kit and injected into the engine only when the system is activated. The extra enrichment is sourced from the fuel system seperately from the injectors and is controlled by jet sizes just like the nitrous. You don't usually need bigger than a 24# injector on a naturally-aspirated street driven 302 because they are good to 400 horsepower. Soooo....30'S are simply way more than you need.

    To sum it up, buy injectors for the projected power level that you'll make before the nitrous, since that's how the engine will spend most of its time. Too big an injector can be just as detrimental as too small: loss of power from a rich mixture, bad idle, accellerated cylinder wear (from the unburned fuel washing the oil off the cylinder walls) are all problems associated with too large an injector.

    A good rule of thumb is keep the 19's until you upgrade the heads, since most other bolt-ons (cam, intake, headers) are within the capabilities of 19's.
    #5
  6. perkys stang

    perkys stang New Member

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    Nothing less then 30's
    #6
  7. Michael Yount

    Michael Yount Advanced Member

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    joncash nailed it I think - 24's are plenty for most any streetable normally aspirated 302. If you're running a wet nitrous kit, then the fuel is supplied separately and the 24's will work. If you run a dry nitrous kit, then the injectors have to supply the extra fuel. So how much injector you need is a function of how much nitrous you're gonna add with the dry kit. 30's will probably cover you up to say a 100 shot. You start going more than that and you'll probably want more injector. However, keep in mind that those larger injectors (including the 30's) have a tougher time metering small amounts of fuel - like at idle and part throttle running - where most of your street driving occurs. I'd think twice about sizing the injectors for a big dry shot of nitrous if I was using the car for a lot of street driving. You haven't provided any specifics of the power output without the nitrous - but if it's reasonably streetable - I'd go with the 24's and then use a wet nitrous set up.
    #7
  8. Black331Stang

    Black331Stang Active Member

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    quick question for michael lol...im sure teh original poster will be interested in thisquestion too...
    just quick...what do u prefer wet or dry?
    #8
  9. Michael Yount

    Michael Yount Advanced Member

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    Depends on the application. For a racing only vehicle, I'd prefer a dry set up. Everything can be optimized for w.o.t. conditions, and engine tuning in the 4000-6500 rpm range (on these engines). For a street vehicle especially a daily driver, I'd prefer a wet set up. I want to run the smallest injector that will meet the engine's needs on the street since the vast majority of the time a street car is barely using it's injector's capacity. I don't want to ask a big injector to deal with very small amounts of fuel. So a dry set up allows me to pick the smallest injector I can get by with, and design the extra fuel system for the nitrous hit separately. But that's just my preference -- others make other choices for different reasons.
    #9
  10. bgwrm89GT

    bgwrm89GT Founding Member

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    Not to change the subject, but does anyone know how much Hp the stock injectors can handle before you have to go to 24's ?
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  11. staticc

    staticc Founding Member

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    very good explenation. i think i might change my order to 24lb mass air/injectors. and when i do step up to nitrous ill have to go with a wet kit.

    thank you.
    hopefully its not too late to change my order around, ill talk to my parts guy on friday.

    and for everyone else. i already have a H/I/C setup.
    #11
  12. QDRHRSE

    QDRHRSE New Member

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    For future reference....

    Go to www.slowgt.com and use the racers math section. You will never have this type of question again :flag:
    #12
  13. Michael Yount

    Michael Yount Advanced Member

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    bgrwrm89 - go here and scroll down for info on injector sizing and what impact increases in fuel pressure have on effective injector rates. http://www.pro-flow.com/tech info/sizing.htm

    You'll get a lot of debate out there from different folks on the topic. But a general rule of thumb is when you start to get over 300HP crank, you're getting close to the limit of the 19's at stock fuel pressure; when you start to get over 400HP crank, you're getting close to the limit of the 24's at stock fuel pressure. That's for normally aspirated applications. When boost is involved, the injector is pushing against not just atmospheric pressure, but also the boost pressure which reduces the effective flow rate of the injector. So, a different set of HP levels apply if you're getting there with boost.
    #13
  14. bmo37

    bmo37 Founding Member

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    vote for 30's
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