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  1. #61
    Senior Member BasicQ's Avatar
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    Doesn't time fly.

    That 7" of idle is still a head scratcher. Dual plane and cam in the 230's at .050"? Cam timing events might reveal something there. wouldn't be surprised if first movement or tip in was opening the generic pcv to full flow, then being a difference at WOT HP, not full closing, something you are assuming as well I guess.

    Some excellent info thanks LX, and up to this point happy days. Interest in getting out putting k's on the 'ol Holden certainly trend upward when it becomes fun to drive again.

    Next time I do a Summit order if you like I'll get a few pcv valves that were used in the solid cammed Chev's of the late 60's early 70's and send to you so you can give it a go. There only about four or five bucks.

    Well done on getting it sorted and if your ever heading to a drag strip let me know and I'll join you.

  2. #62
    Senior Member LXCHEV's Avatar
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    The cam is a Comp Cams Extreme Energy XR288HR (hydro roller) - 236/242 @ 0.050", .555/.576 valve lift, 110LSA.

    Yep agreed - I think the initial movement was opening that particular PCV to full flow - it was absolutely having a huge impact on vacuum at both idle and transition off idle.

    No hurry from my side - but that'd be excellent if you can grab one of the Summit PCV valves with a future order.... I can flick you some cash to post one out my way.

    I would be pretty keen on hitting up Calder Park (or even Heathcote) once all this pandemic stuff settles down. Let's see what we can organise in the coming months!

  3. #63
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    hi
    yup
    Agree on the low vacuum ,this is typical of all the engine dyno reviews that if your lucky they mention "hg vac at 1000rpm let alone at idle. Almost none mention vac at idle . I`m refering to either 383/400sbc that with either 230/236 or 236/242 By all reviews [ scraps of info ] these should make at least 10-12 inches .

    Although u must be on the right track as even the smaller carby size has helped + plugging the PCV .
    Now try a few different ignition curves ,of course 1 change at a time ,,eg try 3or4 different initial timing settings for idle
    Then try to get the timing all in [max advance ] earlier once above is worked out

    Once all thats done see if u can raise the A/F curve by reducing jet size evenly

  4. #64
    Senior Member LXCHEV's Avatar
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    Great feedback, thanks swampy - and yes, the ignition curve will be the next logical thing to play with.

    Just on the idle vacuum too - my car will idle super happy now at ~800rpm (perhaps even a touch lower).... I recall last time I had the vac gauge connected, I did see dramatic improvements very quickly as soon as the revs come up, to say 1,000rpm, 1,100 rpm, 1,200 rpm etc... it's just super low down in the revs where it's really low. Not that it's bothering me anymore now anyway, but always keen to continue refining.

  5. #65
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    hi
    yup its always tempting to go the biggest cam /heads/ big single plain but as your mentioning the driveability goes down . But people do interpret this differently .

    I have gone 400cuin small s/plain , midrange hr cam , 780cfm modest [optional 850] ,big exhaust primaries ,quality cnc modest size heads for eng cubes . Combo should work, the minimum performance combination . More head / cam / carby would give more at 4500 to 6500 rpm but remove drivability at idle and performance at between 2500--4500rpm .

    The trick is with dyno figures is most times the vacuum is at 900--1000rpm

    A 408 windsor with a 240/240 hr claimed about 12 inches of vac but this might have been at a 900--1100rpm idle . Although it may have fallen below this rpm a dual pattern cam should help hold the vac at higher levels with a low rpm .

  6. #66
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    [1] Idle vac seems unusually low for the engine size & cam. Is the cam in retarded position?

    [2] PCV erratic. Struck this problem many times with low vac cams. Here is an easy fix. Cut it open & remove pintle & spring. Braze/silver solder back together with a thin steel disc sandwiched between the halves. Drill a 7/64" hole in the disc. This size correlates to the idle flow. So you can refit the PCV & have reliable idle operation, plus it looks stock for rego....

  7. #67
    Senior Member LXCHEV's Avatar
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    I can't confirm if my cam is retarded or not as it was shop built - but I have no reason to believe it is (of course, who knows!).

    I like the PCV workaround too, noted.

  8. #68
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    Have a look at this guy's PCV valves, not cheap but I like the idea.... http://mewagner.com/

  9. #69
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    hi
    Remove brake booster hose connection and reseal . IE check vac b4 and after connection and the vacuum gauge should not move .

    spray carby cleaner on all carby and manifold joins,, yes it will kill engine paint
    BBQ bottle have regulator hooked up then long hose then to a 1/4 copper wand ,move around and inspect joins for leaks
    Do smoke test , I`ve never done one

    If auto remove and plug vacuum modulator line also .
    Last edited by swampy; 01-10-2021 at 08:38 AM.

  10. #70
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    Quote Originally Posted by struggler View Post
    G'day Brett, it's been a while, good to see you're still around !

    I know this is an unpopular opinion but I still like vac sec carbs for street use. The original 3310 750 vac with the down leg boosters was a great carb out of the box. These days I just buy a second hand 750 vac, fit a Proform main body and a secondary block and run it.

    Again.... JMHO.
    agreed me too, nothing wrong with good vac carb set up right

  11. #71
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    Quote Originally Posted by BasicQ View Post
    I know there hasn’t been any contention over the size (cfm) carby the OP would best be served using but at the same time there has been suggestions of different brands of carby that would best suit the OP as others have had great results and even seen better numbers on the dyno with brand ‘A’ netting higher numbers than brand ‘B’ or ‘C’. I have also lost count of people asking on the big wide world web “what size carb for my engine” and debate ensues as some say “that 950 HP is way too big for your 383!” or “you need something bigger than that 850 double pumper on that 496 you should try 1000cfm”. There are also others that changed from the likes of an 850 Demon to Holley 950 HP and the car goes better and the owner is under the assumption that he needed a bigger carb all along. But what 950 is too big and was that 1000 change really a step up in cfm?
    CFM is regulated by the venturi diameter at its smallest point and throttle bore size. Type and placement of booster has an effect on cfm too but the below list all have down leg boosters. The list shows that quite often the cfm number is nothing more than a designated name or a number assigned to a carby by the advertising dept to differentiate from like cfm carbies. When choosing cfm for performance it’s a good idea to dig deeper and see what constitutes that cfm number.
    To the OP use this list when deciding cfm over several popular brands.

    Venturi is first number - throttle bore second

    750 cfm
    Holley Ultra XP 1.376” - 1.688”
    Street HP 1.376” - 1.688”
    Demon 1.400” - 1.688”
    Quickfuel S/S 1.375” - 1.687”
    Quickfuel Q series 1.390” - 1.687”
    Brawler 67200 1.390” - 1.687”
    Brawler 67257 1.375” - 1.687”

    850 cfm
    Holley Classic HP 1.56” - 1.688” (named 830cfm)
    Holley Double Pumper 1.56” - 1.750” (does have choke horn)
    Holley Ultra and Ultra XP 1.56” - 1.750”
    Holley Street HP 1.56” - 1.688”
    Holley Track Warrior 1.56” - 1.75”
    Demon 850 (any) 1.56” - 1.75”
    Quickfuel S/S 1.56” - 1.75”
    Quickfuel Q series 1.39” - 1.75”
    Brawler 67201 1.39” - 1.75”
    Brawler 67214 1.56”- 1.75”

    950 cfm
    Holley Classic HP 1.376” - 1.75”
    Holley Ultra and Ultra XP 1.60” - 1.75”
    Holley Street HP 1.56” - 1.75”
    Quickfuel Q series 1.450” - 1.75”
    Brawler 67202 1.450” - 1.75”

    1000/1050 cfm
    Holley HP 1.56” - 1.75” (named 1000 cfm)
    Quickfuel Race Q 1.59” - 1.75” (named 1050 cfm)
    Brawler 67209 1.59” - 1.75” (named 1050 cfm)

    You can see that if a range of either 850’s or 950’s were tested on a dyno on the same engine those guys testing would come to the conclusion a certain brand or type of carby was better than another. If all were optimized it may well have been the venturi and throttle bore combination that the engine best responded to despite the brand name on the carby. A Demon 750cfm, Brawler 850cfm 67201 and a Holley 950cfm HP Classic would be closer in actual cfm than their name suggest.

    For CFM 750 and above oils ain’t oils.

    Hope this helps.
    yes spot on great info there, not all carbs are created equal

  12. #72
    Sure why not? 76lxhatch's Avatar
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    Quote Originally Posted by struggler View Post
    Have a look at this guy's PCV valves, not cheap but I like the idea.... http://mewagner.com/
    I have one, it works

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