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  1. #1
    casual poster STOKESY77's Avatar
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    Default What carby mechanical or vacuum Holden 355 with TH350 transmission

    Hi all,

    What carby to choose for my 355 build? I'm running a TH350 transmission and have heard that vacuum secondary carbs are better suited to auto transmissions but I was looking at a 780cfm Pro Systems mechanical secondary and was just wondering will it be ideal with the auto transmission? Running a Crane F-280-2 solid, Allstar 3500+ hi stall, 9" diff with Trutrac centre and 3.89 gears, Harrop single plane hi rise with 1" spacer.

    Cheers, STOKESY
    Last edited by STOKESY77; 02-12-2021 at 05:39 PM.

  2. #2
    Do you ever leave? EH179's Avatar
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    Nothing wrong with a mechanical secondary carb on an auto trans, providing (in your case) you set the kick down cable up right.

    I have run a similar combo' to yours with the 780 Pro Systems and it was a great street setup.

  3. #3
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    Quote Originally Posted by STOKESY77 View Post
    I'm running a TH350 transmission and have heard that vacuum secondary carbs are better suited to auto transmissions.
    I would say that comment is more the opposite if your looking at it from a longevity kind of view.

    Thats splitting hairs and I wouldn't pay any consideration to it, either would be fine.

  4. #4
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    Hi
    I suspect it comes from people fitting mech sec carbs to standard type vehicles . Well modified vehicles have rear gear and convertor stall . These mods allow the carb to unleash the air flow quickly and get away with it .

  5. #5
    Part of the furniture BasicQ's Avatar
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    780 will be good.

    No matter what carby you end up getting do some homework with dyno tuners to see if they do more than change main jets. Having a tuner that’s knowledgeable on changing IFR and air bleeds to dial in to your combo properly is well worth the money.

    EH179 could probably give you a recipe for that carb as a starting point?

  6. #6
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    I had the 780 pro systems on my very similar 355 (manual) and it was good. It will be going back on the next up specced version.

  7. #7
    casual poster STOKESY77's Avatar
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    Thanks everyone for your thoughts and comments will definitely go the Pro Systems 780cfm mechanical secondaries and also a AFR gauge setup like one of these https://www.summitracing.com/parts/avm-30-4110 EH179 what size jets are you using in your Pro Systems 780 and were they the ones that came with it or did you have to change them? Did you have to do much to it out of the box?

    Cheers, STOKESY
    Last edited by STOKESY77; 03-12-2021 at 12:33 PM.

  8. #8
    Part of the furniture BasicQ's Avatar
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    Default What carby mechanical or vacuum Holden 355 with TH350 transmission

    Quote Originally Posted by STOKESY77 View Post
    ...... and also a AFR gauge setup like one of these https://www.summitracing.com/parts/avm-30-4110

    Cheers, STOKESY
    I can recommend that one. Good quality, easy to use, pi55 easy to install at a reasonable price.


    Sent from my iPad using Tapatalk

  9. #9
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by STOKESY77 View Post
    Thanks everyone for your thoughts and comments will definitely go the Pro Systems 780cfm mechanical secondaries and also a AFR gauge setup like one of these https://www.summitracing.com/parts/avm-30-4110 EH179 what size jets are you using in your Pro Systems 780 and were they the ones that came with it or did you have to change them? Did you have to do much to it out of the box?

    Cheers, STOKESY
    STOKESY, the carb was pretty good out the box on that combo i had and i actually picked up 2/10ths and 2 mph down the qtr as is.

    That carb is now on a diff' combo' and being a slightly more efficient engine, the jetting was dropped from 74-84 to 72-82 and the iab's went from 70's to 80's.
    Same ifr, mab's, and pvcr, no other changes needed.

    If you ever need help tuning this, feel free to ask or contact Patrick via email, his after sales service is good.

  10. #10
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by BasicQ View Post
    780 will be good.

    No matter what carby you end up getting do some homework with dyno tuners to see if they do more than change main jets. Having a tuner that’s knowledgeable on changing IFR and air bleeds to dial in to your combo properly is well worth the money.

    EH179 could probably give you a recipe for that carb as a starting point?
    Thanks for the endorsement

  11. #11
    Part of the furniture BasicQ's Avatar
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    Quote Originally Posted by EH179 View Post
    Thanks for the endorsement



    Sent from my iPad using Tapatalk

  12. #12
    casual poster SLE355's Avatar
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    Quote Originally Posted by BasicQ View Post



    Sent from my iPad using Tapatalk
    Who do you recommend around Melbourne?

  13. #13
    Part of the furniture BasicQ's Avatar
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    Quote Originally Posted by SLE355 View Post
    Who do you recommend around Melbourne?
    I’m in Geelong and highly recommend Dalton Automotive if your in this region. Chris is a drag racer himself.

    Melbourne, I’d have good faith in LXCHEV’s guy in Goody’s Garage.
    Last edited by BasicQ; 05-12-2021 at 07:54 PM.

  14. #14
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    Lakeside auto in Reservoir are pretty good Stokesy..

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