Would I benefit fron stepping down to 24 lb injectors?

Discussion in 'Fox 5.0 Mustang Tech' started by mike93lx, Jan 21, 2004.


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  1. mike93lx

    mike93lx New Member

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    When I had my motor built, my engine builder and I agreed to go for 30 lb injectors so I wouldn't have to upgrade them right away when I got a blower. Well, I hate to say it, but the blower is going to have to wait a while and I was wondering if stepping down to a 24lb injector and recalibrating my meter would actually help me out. Any opinions on this? I haven't had the car on a dyno yet to check the A/F curve, but the car doesn't seem to be running rich except maybe a little on the bottom end, but that may also be my cam.
  2. mike keirstead

    mike keirstead New Member

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    Have it dynoed. There is no way to really tell. With you h/c/i combo I can't see the 30s being to big.

    But you do have low compession. So the best way to tell would be a WIBE BAND o2.
  3. Highbredcloud

    Highbredcloud New Member

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    I agree with Mike...30# won't be too big. Just use the stock fuel pressure at around 38-40psi and you will be fine. Not really worth recalibrating the MAF and spending
    $100.00 you'll be fine.
  4. 86Cobra

    86Cobra Founding Member

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    30s are fine for that motor. When you get a blower you're going to need a lot more than 30s.
  5. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    The 30's will be fine...but if you just want to spend the money 24's might give you some better fuel pressure and also possibly solve the running rich at lower rpms....if you don't already have one get an AFPR to help out...

    Yeah probably when you get the blower you will need 36 or 42lb injectors...

    David
  6. perkys stang

    perkys stang New Member

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    What he said.. and then some..
  7. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    Can you explain better fuel pressure with 24#??? I'm confused....
  8. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    I've understood (looking at his combo)...that it could be benificial to have better fuel pressure which would mean stepping down to 24's...

    For Example: 24lb - (with AFPR) set pressure to maybe 42?
    30lb - (with AFPR) set pressure to maybe 35?

    He would be perfectly fine with those 30's on there though....it was a suggestion.... :shrug:

    David
  9. raph130

    raph130 Founding Member

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    my friend put 30lb injectors, 70mm maf and at stock fuel pressure which is extremely too high, dynoed at 90rwhp. stock fuel pressure on huge injectors is a no no and just made the engine hesitate all the time. after bringing the base fuel pressure down to 15psi, wot is 20psi, it dynos at 250rwhp and could still use a little bit more leaning out. are you guys crazy? 40psi on 30 lb injectors? MY GOD. thats for extreme boost only. 30lb injectors are good for almost 600HP. your gonna want to run the base fuel pressure no higher than 15psi.
  10. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    Something is wrong with your friends car...

    I have 30lb injectors on my h/c/i at 39psi...and runs very nice...

    And how did you all of a sudden get a fresh 302/AFR 185's/etc...hmm...fishy...
  11. raph130

    raph130 Founding Member

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    see the asterisk? it means those are mods i haven't done yet. there is nothing wrong with my friends car. 30lb injectors can support just about 600hp. you never use stock fuel pressure as a base line with bigger injectors. you go lower. btw, if i *all of a sudden* wanted aluminum heads all i have to do is go to the website put in my credit card number and hello...all of a sudden in a few days will arrive my new heads.
  12. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    Yeah I seen the astericks after I posted it...might want to pint that out in your sig. for future reference...

    Your wrong about the bigger injector/lower FP theory...My car liked the bump from 36psi to 39psi (it is what the computer expects)...

    Sounds like your friends car didn't need 30lb injectors to begin with...

    There is a lot more to a 600hp capable injector on paper...you have to worry about ECU air/fuel curves/duty cycles/out running the injectors/etc...

    Stock fuel pressure is the best baseline there is to start with...if you have the proper size injector...
  13. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    BTW if you have a place that can deliver the AFR 185's within a few days...btw tell me... :D

    I was just referring to how some of your post have been in the past...fishy and unreliable...don't take offense to that...
  14. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    5spd GT if you need AFR's quick let me know;)

    raph, something is wrong with your friends car. First adjusting Fuel Pressure only changes it at WOT, and at 15psi you have little to no spray pattern it is dribbling out of the injector. The stock EEC will adjust the pulse width of the injector based on the readings from various sensors and a factory fuel curve, after a few cycles no matter what you set the FP at the EEC will take over to try to get the car to a "stoich" setting.

    30# inj are near dead on a 340RWHP car I have the datalogs to prove it.... 36# inj nearly maxed out at 425RWHP. Both of the above numbers are based on a 85% injector duty cycle at 42# of FP vac off.

    If the car is LEAN down low or mid range you need a LARGER inj, it will provide more fuel based on a stock curve.

    If the car is LEAN up TOP at WOT, you need to increase the pressure or swap to a LARGER injector. Adding pressure will help only so far once you get into the high 40's.

    For a 600HP car I would have a low impedence 72# injector personally, although you could get by with a 50#-55# high impedence inj.
  15. Michael Yount

    Michael Yount Advanced Member

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    Sounds to me like it ain't broke - and if it ain't broke --- don't fix it.

    Leave the fuel pressure at the stock level - 38-40 psi. It's where the ecu and the maf expect it to be. There's no reason to mess around with fuel pressure. The ecu controls mixture using the O2 sensors. If you try to richen it up or lean it out by altering pressure, the ecu will simply decrease or increase pulse width to get the mixture back where it wants it. And over time, it will change the data that impacts w.o.t. mixture as well when it's ignoring the O2 sensors. Don't mess with the fuel pressure.

    If you've got verified mixture issues (via wide band sensor data), be sure the fuel system is adequate (pump, injectors), and make the proper adjustments via chip/twEECer in the ecu, or get the maf transfer function data loaded into the ecu.
  16. raph130

    raph130 Founding Member

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    jegs delivers pretty quick. i have ordered from them a few times. my friend didn't need the injectors at the time he got it. he got it because he is planning on twin turboing his stang this winter in the garage and putting down 600rwhp. it is a self fabrication project. all in all he'll be spending about $700. they are brand new t3 turbos, mandrel bent tubing bought from ebay extremely cheap, lots of other things have been bought from home depot like intake tubing which will be done with very lightweight copper. we found a junk yard that has turbo cars with intercoolers the size of a big radiator! of course there are lots of normal sized ones also. he has been working on preparing the engine in the mean time. all he has into the engine right now is a cam and maf and tb and 30lb injectors. he's getting the new bbk mustang intake for it next month.

    i have a new stock fuel pressure regulator and 24lb injectors and maf calibrated to them. my car runs so rich you can smell it blocks away. its extremely strong, and the dyno even pointed it out that there is much excess unburnt fuel. maybe your car is fine but imsure you could lean it out a bit. stock fuel pressure is overkill on my car and i just have 24lb injectors.
  17. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    Jegs doesn't have AFR 185's...

    Well it doesn't sound like the best/reliable matched combo but whatever he/you want to do...I've haven't ever changed your mind :)
  18. raph130

    raph130 Founding Member

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    in fact they do since it was at jegs website where i chose which head i wanted to go with. they run $1374.99 part number 033-1422 and 033-1492

    http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=328623&prmenbr=361
  19. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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    Something isn't right if you can smell if from blocks away...exageration I'm assuming :D

    Your rich problem isn't the injectors fault...either a bad calibration/if at all or something else is wrong...your car would not be rich like that and if it was you would be fouling plugs left and right...
  20. 5spd GT

    5spd GT "the 5.0 owns all" Founding Member

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