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Thread: Holley Jetting.

  1. #1
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    Default Holley Jetting.

    I've been attempting to tune a holley 670SA and I think my primary mains/PVRC are on the biggish side and would like some opinions.
    Eng is a yt pre-pollution headed black 304 with crane 304 hyd cam,sp manifold. 10.5-1 comp.
    Where I'm at.....Swapped out stock pri metering block to a QFT.
    Primary mains 65 to 72
    Secondary mains 68 to 70
    PVRC .045 to .055
    IFR .28 to .23
    PV 3.5
    All air bleeds are untouched,all four idle screws are 7/8 turns out and spark plugs are one colder(6) with light tan colour.
    Any advice is welcome....thanks

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    in the shed buildin shit 3554me's Avatar
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    Default Holley Jetting.

    Whatís it doing that requires a tune ... light tan seems like it would indicate lean
    Whatís SA as Iím drawing a blank


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    Last edited by 3554me; 25-05-2021 at 07:18 PM.
    10.28@131.99 on e85 26x10
    10.34@130.66 on e85 255 radial


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    Street Avenger..Lean emissions carb

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    in the shed buildin shit 3554me's Avatar
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    Default Holley Jetting.

    Thanks

    Idle feeds at .023 would be my first concern they seem way too small , how far open are the throttle blades ?


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    10.28@131.99 on e85 26x10
    10.34@130.66 on e85 255 radial


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    Not the Kingswood! hq308's Avatar
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    Why a 3.5 power valve? That's likely only going to open under fairly heavy acceleration. That would explain why it has such large jets on the primary side. There's generally an 8-10 jet split primary to secondary to compensate for the lack of power valve in the rear but you have more jet in the primary because it's likely the pv isn't opening as early as needed.

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    Do you ever leave? EH179's Avatar
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    So much of that setup sounds wrong, mate.

    Idle feed too small, main jetting all over the place, PVCR too large for that engine, PV too low...

    68p - 76s mj
    50 - pvcr
    6.5 pv
    28 ifr

    That will get you close.

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    Quote Originally Posted by 3554me View Post
    Thanks

    Idle feeds at .023 would be my first concern they seem way too small , how far open are the throttle blades ?


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    Just under a full turn with no slot showing on the secondaries.

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    Quote Originally Posted by EH179 View Post
    So much of that setup sounds wrong, mate.

    Idle feed too small, main jetting all over the place, PVCR too large for that engine, PV too low...

    68p - 76s mj
    50 - pvcr
    6.5 pv
    28 ifr

    That will get you close.
    I know jetting looks all over the place thats why I'm asking. I tried settings same as above but low end was flat,unresponsive and lazy,the bigger I went on the primary side the stronger it got.With the 23thou ifr(primary side only) it's never been smoother at idle and off idle. As for the 3.5PV,7''vac at idle in D.

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    in the shed buildin shit 3554me's Avatar
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    Are the Idle air bleeds adjustable?


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    10.28@131.99 on e85 26x10
    10.34@130.66 on e85 255 radial


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    Quote Originally Posted by 3554me View Post
    Are the Idle air bleeds adjustable?


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    No,I havent touch them,I think theyre about 78thou.I know the mains seem way off,maybe cam has low signal. Camshaft is advanced 4 degrees if that makes a diff.Do the prims and secs need to be balanced on a open plenum single plane?

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    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by 71rocket View Post
    I know jetting looks all over the place thats why I'm asking. I tried settings same as above but low end was flat,unresponsive and lazy,the bigger I went on the primary side the stronger it got.With the 23thou ifr(primary side only) it's never been smoother at idle and off idle. As for the 3.5PV,7''vac at idle in D.
    Hq308 explained above why it went better with bigger pri jets,... that late opening pv.

    You can have a pv rated higher than the engines vacuum ie: you could use an 8.5 pv in your engine and have the pri mains richen up earlier and possibly lower the main jet.
    The power valve does not operate at idle like many think, unless it is leaking.

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    Quote Originally Posted by 71rocket View Post
    Do the prims and secs need to be balanced on a open plenum single plane?
    Yes.

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    Okay,I'll drop the mains by 4 or 5 and 6.5pv but I cant change the pvrc....see what happens.

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    Not the Kingswood! hq308's Avatar
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    The old half idle vacuum power valve sizing is an old wives tale. PV sizing should be based on vacuum at cruise speeds.

    For what it's worth my nugget has around 5" at idle but has a 6.5 PV.

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    Senior Member BasicQ's Avatar
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    Default Holley Jetting.

    Quote Originally Posted by EH179 View Post
    Hq308 explained above why it went better with bigger pri jets,... that late opening pv.

    You can have a pv rated higher than the engines vacuum ie: you could use an 8.5 pv in your engine and have the pri mains richen up earlier and possibly lower the main jet.
    The power valve does not operate at idle like many think, unless it is leaking.
    Quote Originally Posted by hq308 View Post
    The old half idle vacuum power valve sizing is an old wives tale. PV sizing should be based on vacuum at cruise speeds.

    For what it's worth my nugget has around 5" at idle but has a 6.5 PV.
    I'll second and third what EH and hq308 are saying. Power valve selection is best done by observing a vacuum gauge in the car while driving and noting what the vacuum reads when under load conditions. Try it and see what kind of accelerator input returns less than 3.5hg".

    I am thinking Holley instructed power valve selection through stationary idle because it would avoid a whole lot of lawsuits if they told you to drive the car and look at a vacuum gauge that lead do driving up some other poor buggers ass or crash in some other way.
    I don't think Holley have ever said if it is not correct or PV is above idle vac there will be rich idle conditions. Its likely that has been wrongly extrapolated by the general public over the years.

    If your going to stick with this carby then a good place to start (afresh) is to get a set of index drills and map out all of the orifices. If its vac sec it likely started with different IAB pri/sec. And now different metering block pri/sec would be upsetting pri/sec balance and as EH replied it should be balanced. Add to that it is likely different pri/sec venturi diameters being rated at 670cfm so more adjustability would be good.

    The signal your single plane 308 would be providing to this carby I think is likely a lot different than the Holley engineers envisioned when mapping out the calibration for this SA 670. In their mind it may well have been something like 350ci, dual plane with a cam below 220* @ .050.
    Last edited by BasicQ; 27-05-2021 at 10:19 PM.

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