proform secondary guidance

Fuel and Air Systems

  1. 7dart0

    7dart0 Well-Known Member

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    So I have my 750 proform dialed in nice on the primary. My issue is the secondary. then I go full throttle it's lean for a split second then it really richens out to high 10's on my wideband. I'm not sure if I should mess with the PVCR or the Jets

    My engine is a 360 magnum stock bottom end,EQ heads with 2.02 intake/1.60 exhaust valves, performer rpm intake, 1" supersucker spacer, TTI step headers, 2800 stall A904, 4:10 with a sure grip.

    Carb setup is as follows:

    Primary;
    72 jet
    31 squirter
    green cam Hole 2
    30cc accelerator pump
    3.5 power valve
    70 Idle air bleed
    28 high speed air bleed
    Emulsion holes .028,block.028,block
    Idle feed restrictor .028
    Pvcr .059

    Secondary;
    85 jet
    35 squirter
    orange cam Hole 1
    30cc accelerator pump
    blocked power valve
    70 Idle air bleed
    28 high speed air bleed
    Emulsion holes .028,block.028,block
    Idle feed restrictor .028
    Pvcr stock
     
  2. mderoy340

    mderoy340 Well-Known Member

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    What cam are you running?
    What is your vacuum and AFR at idle in N DR and cruise?
    Are the IFRs in the top or bottom of the metering block?
    How many turns out are the idle mixture screws? 4 corner idle?
     
  3. 7dart0

    7dart0 Well-Known Member

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    380HP crate cam which is .230"/.234" @.050",.501"/.513" lift on a 108 centerline.

    idle vacuum 12-13hg, 13:1
    drive vacuum 7hg, 13.8-14.2:1
    unsure of cruise vacuum yet (need a longer piece of vacuum hose). cruise afr is 13.5:1
    IFR at bottom
    about 1 turn out on 4 corner idle
     
  4. mderoy340

    mderoy340 Well-Known Member

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    I hate that cam but that's what you have so here is what I would try.
    Your idle circuit is probably a little lean causing a lean transition when you open the throttle. I would fatten up the idle to 12:1 engine at idle in N fully warmed up and see if this helps. A 35 nozzle in the Sec is already large and not curing the transition as the Sec opens.
    Drop from 85 to 83 or 84 and see if that leans the WOT AFR.
     
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    • 7dart0

      7dart0 Well-Known Member

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      I will try those suggestions, probably wont be until tomorrow though. I will check back in then
       
    • MOPAROFFICIAL

      MOPAROFFICIAL Well-Known Member

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      Secondary pump cam, maybe a longer shot is what you need...or maybe its initial volume increase. Try it.
      Use a pV that is closer to the actual vacuum....after that maybe Pvr's
      Usually 10 jet sizes difference is the norm, you have 10.1 afr? That secondary jet is a little big.
      I would not fatten the idle into a stinky 12.1 to cure it.
      Jmo.
       
    • yellow rose

      yellow rose Doctor of Thinkology.

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      The first thing to fix is that 3.5 power valve. That's where you start.

      I realize it's on the primary side but it's opening WAY TOO LATE.

      Check your vacuum at CRUISE and set the power valve opening under that. Then tune from there.

      Also, don't live and die by that O2 sensor. You can get a lean spot and not hurt anything. I trust plug readings over the O2 for most things, until you are down to the gnats ass for tuning.

      Fix that power valve opening.
       
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      • yellow rose

        yellow rose Doctor of Thinkology.

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        BTW,when tuning for cruise, you tune the PVCR and not the main jet.

        Let me say it this way...set your cruise tune with the main jets. Trim the mains down until you get the cruise perfect, and then tune for WOT with PVCR and power valve opening. Once the opening is set, you don't need to screw with that. Tune cruise with the main jets and WOT with the power valve.
         
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        • mderoy340

          mderoy340 Well-Known Member

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          I suggested fattening the idle up as a test. If it helps the transition then the OP will know what to fix.
           
        • 7dart0

          7dart0 Well-Known Member

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          I picked the 3.5 power valve because that was what half my idle vacuum was in drive, per Holley's suggestion on power valve size.
           
        • MOPAROFFICIAL

          MOPAROFFICIAL Well-Known Member

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          2 inches under vacuum at cruise is where I set mine. Holley and their half this or that doesn't cut it.
           
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          • mopowers

            mopowers Well-Known Member

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            That's a pretty antiquated way of choosing a PV. Where's the vacuum level at cruising speed?
             
          • 7dart0

            7dart0 Well-Known Member

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            I'll check when I get a longer piece of vacuum hose and when the weather clears up.
             
          • mopowers

            mopowers Well-Known Member

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            I only ask because I initially set my PV by going with 1/2 of the idle vacuum. I ended up with a 5.5 using that method. It had a mean lean stumble when accelerating from cruise. When I checked, the cruise vacuum was 18, so I switched to higher PV. The highest I had was an 8.5, so I threw it in and it eliminated the lean stumble completely. It would probably benefit from a 9.5 or 10.5 even.

            Another question is how much initial timing are you running, That seems like a pretty big drop in vacuum from neutral to in gear. How much rpm drop do you have shifting when into gear?
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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            I agree 100%;plus

            I would start with;
            -a minimum cooling system temp of 185. I prefer closer to 200
            -a 10.5PV,
            -and 72/80s
            -And with timing at 28* at 2800, going to 34*by no sooner than 3400
            -And make sure the primary throttle valves are up the transfers to a little taller than wide. Then set the idle speed with timing and idle-air bypass. If that means the idle timing is down to 12*, so what. With a 2800TC in there, as soon as you whack it, your up to 28* at 2800, and the tires light up.
            -Then put the biggest Vcan on there you can find, or mod yours to get at least 20/22*.
            -Now; with 4.10s you can cruise at 30mph@2200 in second gear, with about 40/42* cruise-timing, right where she wants to be. Your vacuum will be way up and with the 10.5PV you won't have to floor it to KD, to accelerate briskly; just lay a lil throttle on it and torque away.
            You may have to upjet the secondaries on long WOT hauls.But around town you will rarely be at WOT for more than 3 to 5 seconds, so a lil lean is mean.
            If you change the thermostat, you may have to rejet just a lil.
            Finally, sneak up on the power-timing.

            EDIT; FWIW: on a streeter;
            With the 10.5PV I might even try #70s.
            I recommend to not tune the primary WOT with the secondaries disabled. You will end up with a PMJ a good size too big, and the secondaries might end up a size too small. The AFR will read right with all 4 bbls open, but the primaries will be fat. I would maintain a front to rear spread in the range of 8 to 10 numbers, for best driveability. I like and agree with what YR says about the PVCR , but it's a one way trip; once it's drilled there's no going back.
            You will know when it's right, cuz when you roll into it, she will be eager to go, no matter if the AFR is a tad lean, and when you mash it, with street tires, they will give up instantly. Well they would if you had 160psi cranking pressure.
            But if the Scr is still 9.5, the Rs will have to get up a lil higher to pull it off in second gear. Cuz thr pressure might be down around 145 with a 70* Ica.
            First gear don't count with 4.10s and a 2800,...... cuz even a 4bbl otherwise-stock smogger-teen can spin that A-body combo,lol.
            I ran the 292/292/108 cam for a few months in my 4-speed streeter, but it came out at summer's end. Great power at 5000 plus rpm, put no so good at the rpms where I spent most of my time... With 3.55s, the power didn't come on until 40 mph....in first gear and she was done at 60. Since I was keen on keeping the 3.55s (lots of hiway driving) I got rid of that bruiser. Great cam; lots of power, (dump the clutch and spun to redline around 60 mph), but wrong application for me.
             
            Last edited: Apr 15, 2019
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            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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              5 to 6 inches of idle drop is a red-flag to me. I think your primary t-valves are too far closed. The Transfer-port exposure should be a little taller than wide. Set the idle-speed with idle-timing and idle air bypass, with the primary mixture screws set in the approximate center of their range. If that means you have to close the secondaries, then, so be it.
              The idle-speed should not drop 150rpm going from N/P to in-gear; 75 to 100 is more like it with a 2800TC
               
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              • yellow rose

                yellow rose Doctor of Thinkology.

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                Holley has been wrong way more than they were ever right. You set power valve opening from cruise vacuum and set your cruise A/F ratio with the main primary main jet. Set your WOT A/F ratio with the PVCR and secondary main jets.

                Bet Holley never told you that either, because I've never seen them put it in writing.
                 
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                • crackedback

                  crackedback FABO Gold Member FABO Gold Member

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                  A 13 jet spread primary to secondary????

                  Most of the time that is in the 7-10 range

                  I'd put an 80 jet in it and see where it lies.
                   
                  Last edited: Apr 15, 2019
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                  • 7dart0

                    7dart0 Well-Known Member

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                    I'll pull the carb and check the t port. I'm pretty sure I set it square and adjusted the secondaries for idle. I'll also adjust the rear jets down.
                     
                  • AJ/FormS

                    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                    With that cam you will need a lil more Transfer exposure, probably a little taller than wide.
                    The thing about the transfers at idle is; that you are trading mixture screw adjustment for transfer fuel. If you get too far up the transfers, then your mixture screws will need to be dried up. If you are too far down, then your mixture screws will have to be opened up to compensate. This low-speed circuit never stops working as long as air is moving thru the bores. So around 2200 with that cam, your vacuum will peak. You can set your mixture screws there, somewhere in their range, for best AFR. Then reduce the idle speed and set the Transfer slot exposure for best quality idle. Now you got both ends covered. If the idle speed is not right, set it with idle-timing and idle air bypass. If you change the idle air bypass, then it's back to 2200 and repeat.
                    I wouldn't pay too much attention to the AFR below the rpm of peak vacuum; cuz there is so much crap going on in the intake with that cam, I doubt you'll ever get it right. As long as you don't have tip-in problems, she's good to go;
                    Like YR says;
                    IMO,
                    the biggest error I see Streeters do, is trying to run a lot of idle timing. Yeah sure that wakes her up, but with a 2800TC there is no good reason for that, cuz she's never gonna be asked to pull from idle to 2800, so why make life hard. Remember, at idle, with the intake full of reversion, she might like 30 plus degrees of timing If you had a 1600rpm TC locking the engine in there to 20mph, yeah, lots of timing would be a good thing. But with 4.10s and a 2800, you just step on it a lil harder and torque thru it.
                    IMO, the T-slot to mixture screw adjustment sync. takes precedence over idle-timing.
                     
                    Last edited: Apr 15, 2019
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