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Jet Sizes for Holley 390 Main and Secondary

Discussion in 'Modified Alpine' started by Rockonp04, Jun 29, 2020 at 1:59 PM.

  1. Rockonp04

    Rockonp04 Platinum Level Sponsor

    I am looking for recommendations for main/secondary jet size for my Holley 390. I've already changed my power valve to 4.5 and I ordered 56 jets for the time being because I think I am running lean. I put in a metering block and would like jet recommendations for the secondaries too. Any input would help.
  2. Barry

    Barry Platinum Level Sponsor

    You need to KNOW what your air-fuel ratio is doing under various conditions before you start blindly changing the power valve and jets.

    Either install wide-band O2 sensors in both collectors or have your car tested at a chassis dyno facility with the capability to monitor AFR.
  3. Rockonp04

    Rockonp04 Platinum Level Sponsor

    Yea I understand the process but wanted to know what everyone else is running to give the tuner a good starting point.
  4. 260Alpine

    260Alpine Silver Level Sponsor

    56 is what the MG guys use in the GM 2.8-3.4 V6. Stock secondary metering plate jet equivalent is 58. The Holley needs more fuel pressure also. 5-6 psi. the 4 cylinder usually had 3-4 psi.
  5. Rockonp04

    Rockonp04 Platinum Level Sponsor

    I've got 7 psi fuel pressure.

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