Register now to get rid of these ads!

Technical carb

Discussion in 'The Hokey Ass Message Board' started by 65pamie, Dec 16, 2022.

  1. 65pamie
    Joined: Feb 4, 2011
    Posts: 3

    65pamie
    Member
    from Colorado

    which carbeuretor is better a 750 holley or a 650 edelbrock ? its on my 327
     
  2. 65pamie
    Joined: Feb 4, 2011
    Posts: 3

    65pamie
    Member
    from Colorado

  3. dana barlow
    Joined: May 30, 2006
    Posts: 4,916

    dana barlow
    Member
    from Miami Fla.
    1. Y-blocks

    The intake used in photo,dose not work well on the street{ low end is poor.,too much space under carb, but works well at the drag strip.

    Likely both carbs are too BIG for 327.= nether is better;
    CFM,for a 327 should not be over about 600,except if super mod's* have been done.?
    As for carb designs,both when in good shape*,work well on engines they fit.
     
    Last edited: Dec 17, 2022
    rattlecanrods, Deuces, i.rant and 9 others like this.
  4. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    Neither, and what Dana said.

    Unless it has a very large cam, some serious port work, and you intend to run it at sustained high RPM, you only need a 500cfm carburetor.

    That should be sitting on a dual-plane manifold.
     
    Deuces, i.rant, 65pamie and 6 others like this.

  5. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    Also, I noticed that you have centerbolt heads (often mistakenly called Vortec, but that's not what you have).

    Those are from either a 305, or a 350. If they were sourced from a 305, they have large lumps in the intake ports, to create tumbling of the intake charge.

    They are NOT high flow heads.

    While that is fine for the street, what might not be is that they have 58cc combustion chambers. The average size of a combustion chamber in the 327 era was 68cc (some were smaller).

    On a 4-inch bore, with about that stroke, 10cc's equals roughly one point of compression ratio.

    You may have just raised your compression by one-full-point. Depending on what pistons are in there, you may now have unacceptably high compression.
     
    65pamie, 427 sleeper and dana barlow like this.
  6. 4 pedals
    Joined: Oct 8, 2009
    Posts: 921

    4 pedals
    Member
    from Nor Cal

    If you have both carbs already sitting on a shelf, the Edelbrock is the better option because it limits airflow to demand. If you're looking to buy, something in the 450-500 cfm range is more appropriate.

    Devin
     
  7. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,797

    Mike VV
    Member
    from SoCal

    What Dana said...100% !!
    See below...

    Mike


     
    aircoup likes this.
  8. The Holley is the one that will limit airflow to demand due to the vacuum secondaries. An Edelbrock AVS sort of does that with airvalve on the secondaries, but not as well as the Holley in my experience...
     
    65pamie likes this.
  9. HEATHEN
    Joined: Nov 22, 2005
    Posts: 8,233

    HEATHEN
    Member
    from SIDNEY, NY

    The AFB style Edelbrock carburetors also have counterweighted air valves in the secondaries.
     
  10. HEATHEN
    Joined: Nov 22, 2005
    Posts: 8,233

    HEATHEN
    Member
    from SIDNEY, NY

    Also, there's no such thing as a "650 Edelbrock ", unless it happens to be the AVS version. 500, 600, 750, and 800.
     
    gimpyshotrods likes this.
  11. Budget36
    Joined: Nov 29, 2014
    Posts: 10,806

    Budget36
    Member

    Minor correction, the 350’s had larger combustion chambers, 63-5 cc.

    edit: just speaking of F bodies.
     
    65pamie likes this.
  12. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    I was speaking of the 305 heads as being a potential issue.
     
    Budget36 likes this.
  13. bchctybob
    Joined: Sep 18, 2011
    Posts: 4,443

    bchctybob
    ALLIANCE MEMBER

    It seems to me that before you make a carb choice you may want to research what you have, engine-wise. See if you can get some engine numbers off of the pad on the front of the engine on the passenger's side, maybe a casting number off of the block (back behind the distributor) and heads (pull off a valve cover). Post the numbers or pictures. Maybe some info from the engine builder?
    That info will help to determine what you have as far as the short block and heads.
    That intake manifold is probably overkill for your engine but that doesn't mean it won't run ok, it just won't perform at its best. An Edelbrock Performer or Performer RPM (or equivalent) with a 600 cfm Edelbrock or 600 cfm Holley carb are the most commonly seen setup these days. Both are easy to find and not too expensive. But knowing more about the engine is essential to making a good choice.
    Diggin' those white fenderwell headers!!
     
    olscrounger and gimpyshotrods like this.
  14. blue 49
    Joined: Dec 24, 2006
    Posts: 1,637

    blue 49
    Member
    from Iowa

    I tried an Edelbrock 500 cfm on a 305 and didn't think much of it, performance wise, compared to the stock 2bbl.
    My 327 did not like a Holley 750 I tried on it. Also tried a single plane intake and it wasn't happy. It is now very happy with a Performer RPM manifold and a Holley Street Avenger 670 CFM carb. My 327 has 462 double hump heads (unported) and a Comp Cams Extreme Energy cam and flat top pistons.

    Gary
     
    Algoma56 likes this.
  15. So, what's the difference between the Edelbrock AFB and AVS carbs. Asking for a friend...
     
  16. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    That's probably because the 2-barrel was probably also 500cfm.
     
  17. carbking
    Joined: Dec 20, 2008
    Posts: 3,498

    carbking
    Member

    This in a hot rod forum, so most folks here will answer an ambiguous question such as this with a performance answer.

    But we are also getting questions from folks building non-hot-rods, as chatter on the internet seems to favor answers from folks on this forum.

    In any event, BEFORE worrying about selection of a non-stock carburetor, the enthusiast should consider:

    Current state of tune of the engine
    Proposed state of tune of the engine if other mods are projected
    Use of engine: street, high performance street, straight-line racing, circle racing, BENCH racing
    Type of transmission
    Mass of vehicle for which the engine is being built

    Once these questions have been answered, one can determine desired carburetor size

    As to brand of carburetor: generally best to choose that brand which the enthusiast, or the mechanic used by the enthusiast, feels the most comfortable doing modifications and tuning!

    Jon
     
  18. poco
    Joined: Feb 9, 2009
    Posts: 993

    poco
    Member
    from oklahoma

    Ifind that holly is better than edelbrock
     
    Deuces likes this.
  19. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 11,032

    Johnny Gee
    Member
    from Downey, Ca

  20. X-cpe
    Joined: Mar 9, 2018
    Posts: 1,650

    X-cpe

    LOL
     
    X38 likes this.
  21. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    For racing, maybe. For the street, I find that the opposite is true.
     
    olscrounger, twenty8 and VANDENPLAS like this.
  22. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    None do.

    All engines suck.
     
    Deuces likes this.
  23. The AFB (Aluminum Four Barrel) and the AVS (Air Valve Secondary) both have vacuum operated secondaries. They mainly differ in the way the secondary opening rate is controlled.

    The AFB has a counter-weighted secondary air valve and works quite well when mated to the correct application. But there are a lot of variations of these carbs to consider if swapping to a different engine combo. You can adjust the secondary air valve opening rate but it can be a tedious procedure. But the changes are more permanent and not easily reversible.

    The AVS uses an easily adjustable spring-loaded secondary air valve. It adjusts in essentially the same way as the secondary air valve on a Rochester QuadraJet. You just change the tension on the spring with the carb still on the engine. And that makes it very easy to adjust to the differences between using an automatic or manual trans, a stock or high stall torque converter, a 2400 lb. car and a 3800 lb. car, a 3.08 or a 4.56 rear axle ratio, etc.
     
    Budget36 likes this.
  24. carbking
    Joined: Dec 20, 2008
    Posts: 3,498

    carbking
    Member

    I realize we are not discussing Carter AFB's in this thread, however, lest the comments might be found by some to bleed over to genuine Carter.

    I personally find the AFB secondary much easier to adjust than the AVS, however I recognize that the average enthusiast will not have the parts inventory that I have readily available.

    When adjusting the air valve on the AFB, it is very important to understand the air valve function, and look at how Carter ENGINEERS solved adjustment.

    I have had AFB's come in where the weights on the air valve were ground to almost nothing, and conversely, where additional weight had been added; when changing the mass of the weights was the incorrect approach.

    In general large displacement, relatively lower RPM engines require a lower attack angle than lower displacement, high RPM engines ("torquers" versus "screamers").

    Example: put a "Chevrolet" AFB on a Pontiac, and expect a secondary transition hesitation. Conversely, placing a Pontiac AFB on a Chevrolet, and the engine will not increase RPM's as quickly as it should.

    Borrowed from the signature block of a friend on a different forum: "engineers do things for a reason".

    Carter produced dozens of different attack angle / weight combinations.

    If one has the inventory, and understands what Carter was doing, pretty easy to install the correct air valve assembly. As Clay mentioned, unlike a spring that can fatigue, once the correct air valve is installed; it never goes out of adjustment.:)

    Many may be unaware that Carter offered the AVS as an aftermarket carb once the TQ allowed Chrysler to switch and still pass smog emissions; but while they are listed in the catalogs, Carter sold so many of them ;) that in more than 50 years, and thousands of AFB's, I have yet to see an aftermarket AVS!!!!! Wonder why?:p

    Jon
     
    rattlecanrods, ClayMart and jimmy six like this.
  25. Interesting... I've only seen one AFB with an air valve on the secondary and that was from a 430 Lincoln many years ago. Guess all the rest that I've torn apart have had that part removed over the years.

    And I know how AVS carbs. work, I've got two of them on the Cad 390 in my '40...
     
  26. Yikes. :eek: All this discussion about AFBs gave me a flashback to an old thread about the actual existence of a true vacuum secondary AFB!

    https://www.jalopyjournal.com/forum/threads/carter-carb-id-help.518708/#post-5720090

    And I'm pleasantly surprised that I even remembered about it from way back in 2010!
    :rolleyes:
     
    warbird1 likes this.
  27. HEATHEN
    Joined: Nov 22, 2005
    Posts: 8,233

    HEATHEN
    Member
    from SIDNEY, NY

    Yes, I've found Edelbrocks to be a "set it and forget it" carburetor. Once they're dialed in, they tend to stay that way for quite a while.
     
    gimpyshotrods likes this.
  28. moparboy440
    Joined: Sep 30, 2011
    Posts: 983

    moparboy440
    Member
    from Finland

    What cam do you have?
     
  29. moparboy440
    Joined: Sep 30, 2011
    Posts: 983

    moparboy440
    Member
    from Finland

    A 500cfm 2-barrel does not flow nearly as much as a 4-barrel.
    carb.jpg
     
    aircoup likes this.
  30. gimpyshotrods
    Joined: May 20, 2009
    Posts: 22,285

    gimpyshotrods
    ALLIANCE MEMBER

    I am aware, and I know the conversion formula.
     
    aircoup likes this.

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.