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  1. #31
    casual poster BasicQ's Avatar
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    Quote Originally Posted by COM081 View Post

    Warmer?
    Yes, warmer. PM sent.

  2. #32
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    The size of the MAB determines when the main system starts. A smaller MAB will bring in the main cct earlier & vice versa.

  3. #33
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    Quote Originally Posted by GtoGeoff View Post
    The size of the MAB determines when the main system starts. A smaller MAB will bring in the main cct earlier & vice versa.
    Yes of course MAB determines when mains start. It regulates rate of pressure differential between emulsion well and main well and the air that e-bleeds see, not just the air the e-bleeds see. I subscribe to the theory of e-bleed and air bleed function in my previous post not only because it makes sense in my mind of all the research I have done on the topic but it is what is constantly consistent in my own observations and real world testing. At part throttle steady cruise (the throttle angle that produces 70-80-100kp/h to keep things simple and relevant to tuning efforts for cruising) if the AFR is a bit fat I will go down in MAB size to lean that area. That will also fatten up the top end and that is where PVCR size come in for WOT tuning. You can’t test this theory by just blocking MAB and going for a drive as when the mains start it will draw solid fuel. Emulsion bleeds are corrector jets and there will be no correction in play. What you state Geoff is absolutely how IAB works, larger always leaner and shorter period - smaller always richer and longer effect but the interplay between MAB, e-bleeds, the air they introduce and its effects on density and viscosity of the fuel and pressure differential between wells created is not as simple.

    For an experiment if you have a handful of MAB size air bleeds - a range of anything from .025” to .036” try all of them and see how each affect steady cruise throttle response.
    I know when I have used a .028” MAB primary an orange cam and 31 squirter does the job on part throttle response but going down to .025” MAB at the same throttle angles blue cam and 35 squirter is needed. This is in the area of mains start up.
    Also the throttle angle that provides me steady 100kp/h saw .97-.99ish lambda (with BP Ultimate 98) with .070 IAB and .026 MAB. Changing to .025 MAB leaned to .99-1.01ish lambda. That will enrichen WOT a few points too.

  4. #34
    casual poster BasicQ's Avatar
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    First video .025” MAB primary

    https://www.youtube.com/watch?v=0FIl...&feature=share

    Second video same stretch of road 10 mins later only change is to .028” MAB.

    https://www.youtube.com/watch?v=L1z2...&feature=share

    Yes they are my Sunday driving socks

  5. #35
    Do you ever leave? EH179's Avatar
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    Basic, what brand of carb are you referring to here?

    I find some of your points in post 33 conflicting to what I have found.

    You go down on MAB size to lean the AFR's?

    To test a range of MAB's of 25 to 36 is going to require some main jet changes?

  6. #36
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    Quote Originally Posted by EH179 View Post
    Basic, what brand of carb are you referring to here?

    I find some of your points in post 33 conflicting to what I have found.

    You go down on MAB size to lean the AFR's?

    To test a range of MAB's of 25 to 36 is going to require some main jet changes?
    Mighty Demon 850 Annular is what’s in the vids but same consistent results with Holley HP and other non annular carbs.

    I can accept that some of my points may be conflicting to what you have found just as what I have found is conflicting to some theories out there but consistent to others.

    I have found going down on MAB size leans the beginning of mains as in the videos but of course richens the upper end as it limits air introduced to main well. Use MAB and MJ combination to get good part throttle ratios and adjust PVCR size to enrich/lean WOT as necessary. Emulsion size and location can be used to trim for smoother AFR.

    The test of 25 to 36 MAB at steady part throttle without jet changes is to get a feel for the effect MAB has in isolation at the beginning of mains flow.

    Carb in videos:

    850 Mighty Demon Annular discharge
    1.56” venturi 1.75” throttle bore
    MJ pri 76 sec 85
    IFR pri .033” sec .033” lower position
    IAB pri 71 sec 71
    MAB pri 25 sec 25
    Emulsion top down .025”, blank, .020”, blank, blank.
    PVCR .063”
    Last edited by BasicQ; 20-09-2020 at 09:59 PM.

  7. #37
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    Alright, think I now have a very basic understanding of what's going on in a Holley, order of operations-wise anyway. Gives me a platform from which to observe and analyse I hope.

    Re jet sizes - you guys are talking about ref number, ie - number stamped on jet, not 'drill size', correct?

    So when you say "74 mainjet", you mean a jet stamped as 74, which is an .081' orifice, correct?

    Have a kit laying around.... guess which jets are missing....

  8. #38
    casual poster BasicQ's Avatar
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    Quote Originally Posted by COM081 View Post
    Alright, think I now have a very basic understanding of what's going on in a Holley, order of operations-wise anyway. Gives me a platform from which to observe and analyse I hope.

    Re jet sizes - you guys are talking about ref number, ie - number stamped on jet, not 'drill size', correct?

    So when you say "74 mainjet", you mean a jet stamped as 74, which is an .081' orifice, correct?

    Have a kit laying around.... guess which jets are missing....
    Yes, stamp number. Use 71, 72 or 73’s whatever ones you have for now until you get some 74’s to give a go. Going down 3-4 sizes won’t hurt anything.

  9. #39
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    Roger that. Ta.

  10. #40
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    Quote Originally Posted by 46Crab View Post
    I don’t mind the cam. You will be surprised how much lift those hydro rollers have under the curve. I’m not sure if the photo of the engine in your car is the 355 or not.

    If it’s not, I’d recommend you get you a good valve job and a decent port job to make the most of the cam. If funds allow some 2.02 intake valves would work well. If not and you are going to stick with the 1.94 intakes, a good bowl cleanup and short turns addressed and blended into good valve job will do the trick. Keep us posted.
    Ok, picked up heads today. They were in shop to machine and install spring heights/pressures, valve seals, valves. Porting work had been done by previous owner.

    [img]https://i.ibb.co/Ns3YqDT/heads-9.jpg[/img]
    [img]https://i.ibb.co/KF4kSkj/heads-6.jpg[/img]
    [img]https://i.ibb.co/ccLVHpM/heads-5.jpg[/img]
    [img]https://i.ibb.co/RNsShBs/heads-2.jpg[/img]

  11. #41
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    Quote Originally Posted by 46Crab View Post
    I don’t mind the cam. You will be surprised how much lift those hydro rollers have under the curve. I’m not sure if the photo of the engine in your car is the 355 or not.

    If it’s not, I’d recommend you get you a good valve job and a decent port job to make the most of the cam. If funds allow some 2.02 intake valves would work well. If not and you are going to stick with the 1.94 intakes, a good bowl cleanup and short turns addressed and blended into good valve job will do the trick. Keep us posted.
    Ok, picked up heads today. They were in shop to machine and install spring heights/pressures, valve seals, valves. Porting work had been done by previous owner.

    https://i.ibb.co/Ns3YqDT/heads-9.jpg
    https://i.ibb.co/KF4kSkj/heads-6.jpg
    https://i.ibb.co/ccLVHpM/heads-5.jpg
    https://i.ibb.co/RNsShBs/heads-2.jpg

    arrgh, can't get pics to display
    Last edited by COM081; 09-10-2020 at 12:03 AM.

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