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Customs Vacuum Advance on 3x2 holly's on SBF?

Discussion in 'The Hokey Ass Message Board' started by goldtele, May 31, 2014.

  1. goldtele
    Joined: Sep 16, 2006
    Posts: 118

    goldtele
    Member

    Hello, I used the search for a while but couldn't find what I was looking for.

    I just put a 3x2 set up on a SBF with Holly carberators. I'm having a hard time getting it tuned up and a very knolegable friend of mine told me not to use a distributor with vacuum advance on it. It's a brand new pertronix dist on there now and he said I should replace it with a dist with mechanical advance.

    Is there any logic behind this?

    Thanks!
     
  2. DrJ
    Joined: Mar 3, 2001
    Posts: 9,418

    DrJ
    Member

    Your distributor has both, mechanical and vacuum advance.
    Use both.
    Hook up the vacuum advance to manifold vacuum after setting your initial timing.
    I think your friend is just repeating misinformation he heard from someone else.
     
    loudbang likes this.
  3. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    tommy
    Member Emeritus

    Vacuum advance won't really help performance or cause an engine to run poorly but it is very helpful on fuel economy for street use. None of the performance dists came with VA in the 60s. We didn't care about fuel economy. We just wanted to go fast. I love the look of the Mallory 2 piece cap and convert them to electronic ign. just for their looks. (no vac adv) I'll live with the poorer fuel economy to get that classic look.
     
  4. goldtele
    Joined: Sep 16, 2006
    Posts: 118

    goldtele
    Member

    Thanks, For the feedback! There is no vacuum ports on the carburetors so the vacuum advance from the distributor is going straight to manifold vacuum. Won't that cause the dist to always be advancing since that's a constant vacuum source?
     

  5. Tedd
    Joined: Jul 7, 2007
    Posts: 122

    Tedd
    Member

    At full throttle, manifold vacuum drops to zero so the vacuum to the distributor would also drop off. If you had a ported signal to use at the center carb, the vacuum to the distributor would be much easier to control. Ported vacuum would also allow for a smoother idle versus using a manifold vacuum source.
     
  6. There is an article in the " Holley 94 social group about how to turn a Holley base plate with an economizer valve port into a ported vacuum advance port. It is a very informative article.
     
  7. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    tommy
    Member Emeritus

    "Won't that cause the dist to always be advancing since that's a constant vacuum source?"

    Yes it will and that is the way it has always been. Have you ever watched how fast the needle on a vacuum gauge moves around when driving around? Your vacuum adv. does the same thing. The split second that you step on the gas the vacuum advance retards the timing while accelerating. As you reach cruising speed the timing is advanced to the cruising position for fuel economy.

    Where are the ported vacuum fans planning to get their ported vacuum from? Can't get it from a Rochester. There ain't no ported vacuum ports to get it from. I looked! Ported vacuum is a product of emissions technology. You said that there is no port on your Ford carb so you have no choice either. The tune up books tell you to remove and plug the vac adv. when you set the initial timing. I used to keep my timing light connected after I reconnected the vac adv. It jumped up off of the tag. I knew that the adv. was working correctly. Ford had a strange vacuum adv. from 48-56 and you need their special carb to make it work. I don't know a thing about how it works other than most people shit can their 56 Ford dists and use a 57 Ford dist. hooked up to manifold vac.
     
  8. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,763

    V8 Bob
    ALLIANCE MEMBER

    Ford used vacuum-advance-only loadomatic distributors from '48 truck/'49 car to '56. These have no mechanical advance, and have to be used with carbs designed for proper loadomatic's low vacuum operation up to about 6" Hg max. Ford switched to mechanical advance with additional vacuum advance in '57 for V8s, but continued loadomatics for many years in 6s and possibly others.
    This may be what goldtele's friend was referring to.
     
    Last edited: Jun 1, 2014
    DrJ likes this.
  9. DrJ
    Joined: Mar 3, 2001
    Posts: 9,418

    DrJ
    Member

    What V8 Bob said, But this is specifically about a SBF.
     
  10. May be I'm wrong but there are 2 types of Vacuum advances, Ported and Manifold. Both do the same thing but in different ways. A ported advance will start to draw vacuum as the motor revs and increases speed up until the rpms and load equal out. A manifold advance will advance when manifold vacuum drops like when you open the throttle. This will equal out when rpms and load even out. Both are designed to advance the spark to handle the increased fuel and air going into the cyl. Not retard the spark.
     
  11. snaptwo
    Joined: Apr 25, 2011
    Posts: 696

    snaptwo
    Member

    There are 3 types , manifold , ported(smog thing) and venturi vacuum . Do a search on venturi vacuum advance , Bernoulli effect , it will 'splain it in detail !
     
  12. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,473

    landseaandair
    Member
    from phoenix

    Non ported (manifold) vacuum advance will retard when under load. Gives you a good idle, retards when accelerating and comes back in while cruising. I really don't see any benefit to using ported vacuum.
     
  13. snaptwo
    Joined: Apr 25, 2011
    Posts: 696

    snaptwo
    Member

    Ported vacuum is a smog deal , shuts off the vacuum at idle ,retarding the timing . You want to get venturi vacuum .
     
  14. I don't have any old cars with vacuum advance. All are Mallorys with Pertronixs in them.

    OOps I take that back. My Fairlane has a MSD but it also does not have vacuum advance
     
  15. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    tommy
    Member Emeritus

    Nobody ever says where to get the special vacuum from. All the theory in the world is no good if you can't get it. The old Ford vacuum advance won't work right without the Ford carb it was designed to work with.

    I don't do theory. It must be practical for me to care about it. Show me exactly where you get the ported vacuum.
     
  16. I have a similar set up on my roadster, new edelbrock intake and original 94`s.
    Modified the center carb for vacuum using the Eaton article as a guide that can be found in the 94 thread.
    Went to manifold vacuum instead and car runs a lot better. Lots of reading to do on ported vs manifold vacuum advance.
     

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