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GM TBI to Holley sniper conversion writeup

Discussion in 'TBI & EFI Conversions' started by 87silveradok20, Apr 23, 2019.

  1. 87silveradok20

    87silveradok20 Full Access Member

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    Truck Year:
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    Truck Model:
    Silverado k20
    Engine Size:
    350
    Hopefully this thread can help someone and feel free to ask questions.

    Anyways I started out with a 1987 4x4 with the tbi 350 and now I have a 370hp 355 running the Holley sniper. I’m going to attempt to go step by step in what I did in regards to each step of the tbi to sniper conversion.


    Fuel system:
    I went the cheap route for my fuel system. I put the three port sensing units without the pump in my tanks then ran normal rubber line from my tanks to the switching valve and from the switching valve to the pump. Then I used high pressure rubber line from the pump to factory filter and from the factory filter to the back of the sniper. For the return I cut the threaded end off of the factory line and ran a normal fuel line from the back of the sniper to where I cut the factory line on the fuel rail. Eventually I plan to switch everything to AN braided steel lines.


    Mounting:
    The Holley sniper bolts right on to a regular 4 barrel carb flange. So to make it bolt up to your factory engine you will need a new intake manifold. I currently am using my factory throttle cable but I feel there is room for improvement with it. It’s working for now tho so I am gonna leave it till I finish up some other projects.

    Wiring:
    For the Holley sniper to work properly you need 4 wires. I ran the power and ground together over to the battery and hooked them in there. I found ignition power in the old harness and used it to power the sniper on with the key and then you need to get a tach signal from somewhere so I ran that wire to my distributor(a normal vacuum advance distributor). I also went through my entire factory wiring harness and removed any wiring that wasn’t needed. The only wires that I kept were oil psi and temp sending unit wires, the brown wire to the distributor, and two ignition power wires(one for the sniper and one for the distributor).

    Other stuff:
    I also used the sniper to control my fuel pump, tach, and electric fans. These functions are optional but obviously very convenient. Another point that’s very important to remember is that if you have a th400 trans your lockdown is computer controlled and obviously if you remove the computer it won’t work. I’m working on figuring out if I can use an output of the sniper to control this or not. If I can’t then I’ll
    Just put a switch on the gas pedal.



    Feel free to ask me any questions you may have or add any experience in from guys who have done something similar. Also let me know what pictures you wanna see.






    Sent from my iPhone using Tapatalk
     
    John-Ryan likes this.
  2. 4WDKC

    4WDKC Full Access Member

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    First Name:
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    Truck Year:
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    Truck Model:
    V10
    Engine Size:
    350
    two delco vortec 96-98 fuel pumps would have supplied enough pressure for the sniper, not sure this was cheaper 2 sending units plus a pump vs 2 moderately priced pumps.
     
  3. 87silveradok20

    87silveradok20 Full Access Member

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    Engine Size:
    350
    That’s the way I should’ve done it and I’m sure I will change it to that way eventually as that is a better setup.


    Edit: I should also add that one of the main reasons I didn’t do that was because the truck was carbed for a little bit in between and that is when I put the sending units in.


    Sent from my iPhone using Tapatalk
     
  4. Mastertech

    Mastertech Junior Member

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    First Name:
    Bob
    Truck Year:
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    Truck Model:
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    Engine Size:
    383
    I switched factory TBI to to FiTech. Had it running weeks ago running fitech fuel pump control wire directly to stock pump then to FiTech fuel command center thats all fine. Client wants his twin tanks, to work and be able switch tanks. sounds easy but I want to get rid of the factory computer and as many wires as I can. Figuring out which wire (or wires) I can use at the switch is getting in my head hard. Worked fine Friday through the stock harness. (New tank switch and control valve). Today it's blowing ECM B fuses. I will figure it out but any suggestions would be appreciated.
     
  5. bluex

    bluex Full Access Member

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    Engine Size:
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    Have a spare pump on hand. The external pumps are intended to be gravity fed an do not like pulling fuel at all, especially that far an through the switching valve.

    I get why you did it an I'm not criticizing you or anything just letting you know it'll be living a short life in that application. If you want to keep dual tanks the cheapest route to that is to feed a sump system with a block mounted pump so that the tank an valve side remain unchanged.
     

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