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Thread: Hardware modifications GM style...

  1. #1
    Super Moderator Six_Shooter's Avatar
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    Hardware modifications GM style...

    Just thought you guys might like to see this.


    This is a TBI that I have helped with (welded it), for a friend of mine, to change some things from previous versions. IIRC this is #6.

    This will be replacing an existing 4 bbl TBI, that is very similarly made, just the fuel system was quite different. We hope the new fuel system layout will help reduce some pressure drop that happens when AE kicks in.








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  2. #2
    EFI GearHead ! EagleMark's Avatar
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    Man that looks like a lot of work! Was it just the old style holly injector issue?

    Very cool work though...

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  3. #3
    Super Moderator Six_Shooter's Avatar
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    No, the old 4 bbl is also made from GM TBIs. We think it was just too much injector for fuel system layout that was used.
    The man who says something is impossible, is usually interrupted by the man doing it.

  4. #4
    Vintage Methane Ejector
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    Cool throttle body!

    Glad to see someone else's work bench looks as bad as mine.

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    Interesting.

    For years I've wanted to build a two or three TB intake using the smaller 2bbl units found on 2.8 truck engines but I never thought about a dual bore unit like that. The smaller bore should be better for response and would be less likely to allow fuel to drop out of suspension provided you can tailor the AE curves correctly. I wonder if there's any advantage to swapping to late / big block injector pods and using pfi injectors with fuel pressure as high as possible to keep droplet size small?

  6. #6
    Fuel Injected! JeepsAndGuns's Avatar
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    Very interesting indeed. I'm intrested in how you connected the throttle linkage. Do you have it set up to where both shafts open at the same rate, or do you have it rigged up like a old 4v carb with mechanical seconairys.
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  7. #7
    Super Moderator Six_Shooter's Avatar
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    Right now the throttle linkage just opens both throttle shafts together. Eventually, we might set it up to be progressive, but I will have to build a progressive injector controller to do that, to reduce possible flooding of the later opening throttle plates.

    We plan to run it about 20 PSIG or so, at WOT, and use the vac ref FPR to bring fuel pressure down for idle. With the current TB, we could get it to either run like a scalded cat with high fuel pressure, or idle along, and have good manners at part throttle with lower pressure, but couldn't seem to get both.

    BTW, it flows over 1100 CFM, dry flow flow.
    The man who says something is impossible, is usually interrupted by the man doing it.

  8. #8
    Fuel Injected! gregs78cam's Avatar
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    That's similar to what I had originally planned for my Camaro, but I decided to keep the linkage simple, and mounted them the same direction and real close.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

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    EFI GearHead ! EagleMark's Avatar
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    Conjoined twins!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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  10. #10
    Fuel Injected! gregs78cam's Avatar
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    Ya know you wouldn't have to make a injector controller if you set the main linkage to be progressive for both shafts. Know what I mean? Make the cable attach to the throttle lever only slightly ahead of the shaft centerline, instead of centering the arc of travel over the centerline. That way you have a slower opening at the beginning for better part throttle control, and faster opening at the end ...... progressive.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  11. #11
    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by gregs78cam View Post
    Ya know you wouldn't have to make a injector controller if you set the main linkage to be progressive for both shafts. Know what I mean? Make the cable attach to the throttle lever only slightly ahead of the shaft centerline, instead of centering the arc of travel over the centerline. That way you have a slower opening at the beginning for better part throttle control, and faster opening at the end ...... progressive.
    Not that kind of progressive, the kind where the larger throttle plates stay closed until the smaller throttle plates are opened a certain amount at which point the larger throttle shafts open quickly. It does require the injectors to be progressive for the larger throttle plates, other wise the fuel puddles above those throttle plates and can cause stumble issues. It's been tried. ;)
    The man who says something is impossible, is usually interrupted by the man doing it.

  12. #12
    Fuel Injected! gregs78cam's Avatar
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    Yea, somehow I missed that they were different size bores. You are right if you wanted the "secondaries" to be progressive. I was just suggesting you make them progressive together.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  13. #13
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by Six_Shooter View Post
    Not that kind of progressive, the kind where the larger throttle plates stay closed until the smaller throttle plates are opened a certain amount at which point the larger throttle shafts open quickly. It does require the injectors to be progressive for the larger throttle plates, other wise the fuel puddles above those throttle plates and can cause stumble issues. It's been tried. ;)
    That would be the first TBI Quadrajet! That is exactly how the Quadrajet carburator works.

    You could open the throttle blades more on the big ones to prevent puddling? But how would you make injectors progressive? Holly did it! There old progressive four barrel had rear injectors turn on later... I found this out using a progresive Holly four barel on a GM system, when the secondaries opened the motor was flooded. Then I looked in at idle and they were filling up! We changed out the progresive linkage and it worked fine. The injector delay must be in the Holly ECM...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  14. #14
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    You make the injectors progressive the same way they were on the LT5/ZR1 engine. When the TPS indicates the secondaries are about to open, bring a 2nd injector driver on line which fires the secondary injectors in parallel with the primaries.

  15. #15
    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by EagleMark View Post
    That would be the first TBI Quadrajet! That is exactly how the Quadrajet carburator works.

    You could open the throttle blades more on the big ones to prevent puddling? But how would you make injectors progressive? Holly did it! There old progressive four barrel had rear injectors turn on later... I found this out using a progresive Holly four barel on a GM system, when the secondaries opened the motor was flooded. Then I looked in at idle and they were filling up! We changed out the progresive linkage and it worked fine. The injector delay must be in the Holly ECM...
    That is the exact reason the linkage is 1:1 between each pair of throttle plates. ;)

    Quote Originally Posted by 1project2many View Post
    You make the injectors progressive the same way they were on the LT5/ZR1 engine. When the TPS indicates the secondaries are about to open, bring a 2nd injector driver on line which fires the secondary injectors in parallel with the primaries.
    That's pretty much what I have in mind, though it would be an external controller, until I can learn how to write code for ECMs.
    The man who says something is impossible, is usually interrupted by the man doing it.

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