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Injector size question.

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  • Injector size question.

    Hi folks. I'm installing a ported Pro Flow XT p/n 7137 on my 355 that should produce close to 450hp. Using an injector size calculator, I went with 35lb Edelbrock injectors. I want to be able to reuse these injectors, at higher pressure, in a 540hp 406 in a few years. I was thinking that by keeping pressure down to 43psi, i could make them work in the 355 for now. Then increasing to 60 psi should work in the larger motor. What do you think? Would I be better off with the 27lb units in the 355?
    Last edited by ASE Doc; 03-08-2018, 10:18 PM.

  • #2
    You should be ok with the 35's.

    29's are used in the older 450HP XT's, and the newer 550HP XT's.
    At 43,861 MPH Elon Musk now owns the fastest car in this Galaxy


    • #3
      Thanks for your reply. I actually meant to say 29lb injectors rather than 27lb. I didnt think that Edelbrock used the 29s at the 550hp level. I know the Pico units are good to about 80 psi. I would say 70psi is safe. That gives them some room for increased flow. I may go with 29s anyway. If my hp calculations are a little generous, the 35s will be too much. I can always ramp up pressure to get more from the 29s if needed. More pressure is better for atomization anyway. I have a strong fuel supply with variable speed pump. It can support plenty of pressure and flow. A lot harder to reduce flow from too much injector.
      Last edited by ASE Doc; 03-10-2018, 01:40 AM.


      • #4
        I belive the 450 and 550 used different fuel regulators, at different PSI settings. The 450 should be the none adjustable one, that has vaccum reference. The 550 should be using the adjustable regulator with no vacuum reference..... I could be wrong.
        At 43,861 MPH Elon Musk now owns the fastest car in this Galaxy


        • #5
          Thanks again BITE ME,

          I have the 35s in a box ready to go back to Summit in exchange for the 29s.

          My fuel supply has plenty of pressure and supply capacity to maintain higher pressure as needed to increase output from the nozzles. I've always leaned toward smaller nozzles and higher pressure as it improves atomization. Smaller droplets are a good thing. I recieved confirmation from Edelbrock tech that the max pressure limit on the PICOs is 90psi. At 70psi, the 29s are effectively 36lb/hr. According to my calculator, this will support 470hp which is more than I'll see from this 355. Experience has taught me that the injector size calculators tend to run high anyway.

          If the 29s end up being too lean and I'm not able to comfortably adjust pressure to cover the gap, I know where to find the 35s.