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Thread: MPFI Conversion Injectors

  1. #1
    Electronic Ignition!
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    MPFI Conversion Injectors

    Hey all. I hope this is the right place to ask this question. Can't find a lot of people that would have the knowledge on a setup like this to ask. I currently have a 1995 Yukon with a Whipple supercharger on the entirely stock 5.7L TBI motor. I'm planning to do a full rebuild soon, keeping the stock engine size, I might move up to 72cc heads for a lower compression ratio. I'm planning on running somewhere around 5-7 psi after I do the rebuild.

    Here's the question. I have an old Edelbrock MPFI manifold setup in my room right now. Scored it off CL. Anyways, I need injectors for it. I was looking at the Magnetti Marelli IWP069 injectors. They have to be the shorty injectors, but do you guys think these would have the right flow rate or capacity for my setup? I'm hoping to be in the 400-500 neighborhood when the rebuild is done with the higher boost, I just want to make sure these are in that range for fuel supply. I will be bumping fuel pressure up to about 45 psi, which these say they flow 46 lb/hr (I believe I read that's at 42 psi, but I can't find where I saw that).

    Also, do you guys think it would be safe to run the stock fuel filter? Stock fuel pressure is around 12-15 psi, but would I encounter a problem when increasing that to 45 psi?

    Thanks for the help. Like I said, I hope this is the right place to ask about this. If anyone has any better resources where I could find information on these types of swaps, I would happily read up. More knowledge the better!

  2. #2
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    The stock fuel filter should work fine. It was used on early PFI cars as well as TBI. Online injector calculators say 46 lbs/hr is good for just under 500 hp at the wheels. I believe the next step up on the Marelli Pico injectors is 60 lbs/hr. http://www.edelbrock.com/automotive/...mponents.shtml

    Just out of curiosity, are you planning to use the Edelbrock controller or go with a GM ecm?

  3. #3
    Electronic Ignition!
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    Quote Originally Posted by 1project2many View Post
    The stock fuel filter should work fine. It was used on early PFI cars as well as TBI. Online injector calculators say 46 lbs/hr is good for just under 500 hp at the wheels. I believe the next step up on the Marelli Pico injectors is 60 lbs/hr. http://www.edelbrock.com/automotive/...mponents.shtml

    Just out of curiosity, are you planning to use the Edelbrock controller or go with a GM ecm?
    Plan is to use the GM ecm. I have the edelbrock harness that splices into the current injector wiring, and controls the 8 injectors. I have a lifetime tune with Wester's Garage, they are the ones who tuned my truck for my 4L60e to 4L80e swap. From what I've seen the IWP069's should be fine for 550 to the crank at 43.5 psi. However, I have an e-mail out to Injector Dynamics to see about their ID850 injectors, which flow 84 psi! Yeah, that would be enough. I'm checking to make sure the impedance style on those will match up with the GM style. If not, I'll either go with the IWP069's, or talk to Wester's about a PCM that they can completely custom tune for the new injector style.

    It never ends.

  4. #4
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    84# injectors seem large so make sure the minimum pw is not so big the engine won't idle. Too big an injector and you can end up too rich at idle with no cure. Nice to hear you're using a reputable company for pcm tuning. Keep us updated.

  5. #5
    Super Moderator dave w's Avatar
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    I would use a Wide Band O2 Sensor (WBO2) to tune the MPFI conversion, see attached screen shot summaries I use for WBO2 Tuning. I would also convert the GM computer for MPFI, see attached Information and Notes .zip file.

    dave w

  6. #6
    Fuel Injected! JeepsAndGuns's Avatar
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    What intake do you have? I wonder if it is something like the one I am using. I am running a bare intake a fuel rails from a edelbrock pro flow efi system. It is set up for those strange short pico style injectors. I wanted to use more easy to find bosch style injectors. All I had to do was make a small little angle bracket to raise the fuel rails just a little bit. this allowed me to use the normal length injectors.
    Doing something like that may open the door to a larger and maybe more affordable selection of injectors.
    There are a couple pictures in this thread:
    http://www.gearhead-efi.com/Fuel-Inj...Getting-closer
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  7. #7
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    I did something similar with a marine manifold that was set up for Pico injectors. I used stainless spacers to raise the rail so I could use stock GM injectors.

  8. #8
    Fuel Injected!
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    Quote Originally Posted by JeepsAndGuns View Post
    What intake do you have? I wonder if it is something like the one I am using. I am running a bare intake a fuel rails from a edelbrock pro flow efi system. It is set up for those strange short pico style injectors. I wanted to use more easy to find bosch style injectors. All I had to do was make a small little angle bracket to raise the fuel rails just a little bit. this allowed me to use the normal length injectors.Doing something like that may open the door to a larger and maybe more affordable selection of injectors. There are a couple pictures in this thread:http://www.gearhead-efi.com/Fuel-Inj...Getting-closer
    I have a Holey 4 barrel EFI manifold. Takes bosch style injectors. Put a 4 barrel throttle body on it. Put 42 lbs/hr injectors in the manifold. It is a 383 stroker engine with LT-4 hot cam. Going to put in my '95 chev pickup.

  9. #9
    Fuel Injected!
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    Quote Originally Posted by rsicard View Post
    I have a Holey 4 barrel EFI manifold. Takes bosch style injectors. Put a 4 barrel throttle body on it. Put 42 lbs/hr injectors in the manifold. It is a 383 stroker engine with LT-4 hot cam. Going to put in my '95 chev pickup.
    Sounds like it will be a good running setup, although your injectors are way too big!!!

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