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where do i hook up the vacuum advance???

Discussion in 'The Garage' started by bigbadchev84, Apr 13, 2005.

  1. bigbadchev84

    bigbadchev84 1/2 ton status

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    ok i got a new quadrajet today and installed it but i dont know where to hook up my vacuum advance. any help would be great, the one i have has no solenoids, electric choke, but i think it has a vacuum choke.
     
  2. highrider_44s

    highrider_44s 1/2 ton status

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    there is a spot at the front of the carb near the bottom check to see that you have no vaccum at a idle but it should come in as soon as you rev it up
     
  3. bigbadchev84

    bigbadchev84 1/2 ton status

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    does anyone have a pic????
     
  4. R72K5

    R72K5 Banned

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    hook it anywhere above the throttle blade shafts in base of carb and not in the base of the carb, it needs to be connected to ported source, ported is above throttle blades in base
    it doesnt really matter which of the ported locations you connect it to,

    good luck
     
  5. PaleRider

    PaleRider Registered Member

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    That`s right if you`re ride is smogged, but if you`re after performance it should be given manifoild vacuum.
     
  6. Fierospeeder

    Fierospeeder Banned

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    why would you want performance at idle? And vacuum advance isn't necessary a smog issue.
     
  7. PaleRider

    PaleRider Registered Member

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    Last edited: Apr 14, 2005
  8. Mad-Dog

    Mad-Dog 1/2 ton status

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    generally speaking the HEI should be connected to a ported vacuum source,
    if it pings at part throttle then manifold vacuum should be used.

    HEI distributors are notorious for using way too much vacuum advance,
    there is anumber stamped on the top of the bracket that indicates how much advance in degrees the can will provide at max vacuum, most (all) have more than 10 degree cans installed at the factory.
    Adjustable cans are nice but not very easily tuneable to the novice, Scoggins Dickey Performance Center in Lubbock,Tx has 10 degree cans for around $14.oo

    The SBC usually enjoys 35 degrees of total advance all in by 3,000 rpm: 10 degrees initial, 10 degrees vacuum and 15 degrees mechanical.
     
  9. Triaged

    Triaged 1/2 ton status

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    As long as you don't have a big cam that doesn't idle well your motor will run better with full manifold vacuum. Just try it yourself it is real easy to do. My HEI spits out about 30* of advance at idle and it works great!!! With the ported vacuum I would have to bump up the idle just to get it to run right.

    Also you are right about the ~35* advance but that isn't how you add it up. You need 10-12* base timing (vacuum plugged) at idle. When you floor it you will have NO VACUUM and so you don't add in. You will need ~25* of mechanical advance. When you get off the throttle at high rpm (crusing on the hwy) you will have much more then 35* advance (somewhere like 45*+) which is what helps gas mileage.
     
  10. Mad-Dog

    Mad-Dog 1/2 ton status

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    "When you floor it you will have NO VACUUM and so you don't add in."

    That's why i don't hook up the can to manifold vacuum......

    That's where your wrong :bow:
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    So if you hook the vac advance up to ported and floor it, what happens?

    Nothing. That is correct. It doesn't matter where you get the advance from, under acceleration/high engine load, you won't get vacuum advance. Ported or not, vacuum is vacuum, and unless you have a reservoir, you won't have advance from vacuum under acceleration. (within reason, I'm not implying you will have NONE, but very little compared to cruise/idle) Anyone that has hooked a vacuum gauge up to their engine and driven around will understand this.

    Whats wrong with high advance at idle? Nothing. High advance smooths out the idle. The problem is high BASE timing which makes a vehicle hard to start. Relatively low base timing makes it easy to start, once the vehicle has started is when the vac advance can "come in" without causing that starting issue. At cruise the vacuum will still be high, so again, manifold or ported, the vac advance will be the same.

    Pull vacuum from a port on the carb or the manifold, it's still engine vacuum. The author of the article cited previously is correct.

    Edit: and because I'm sure this will keep going, and it's already been hashed out millions of times everywhere on the net, read these, so hopefully people don't feel the need to further regurgitate the same arguments:

    Timing link 1

    timing link 2
     
  12. RustyMule

    RustyMule Registered Member

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    My 30 year old 230K mile motor runs smooth as a baby's behind running that advance off of manifold vacuum. It may be different for other people. I was taught, at tech school, to always hook it to manifold vac. But I don't think there will be a consensus on this subject mo matter what. :dunno:
     
  13. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    So what are you guys using as dead timing(without the advance hooked up)?

    Funny this topic came up, I just replace my VA this week and was having problems with what seemed like it advancing too much now(ping under partial throttle). The advance had been out altogether for no telling how long... I threw a timing light on it today and with was well almost 20*above TDC dead timed, I backed it down to 4* and then hooked my advance to ported vacume which now i have a lopy idle without any mods over stock. I'm definatly going back to full manifold vacume but curious where to start with the dead timing and maybe avoid some pinging....

    Also a item to check is on stock manifolds the pass side manifold has a "flapper valve" so to speak that under load closes up some and is wide open when not under load, it seems a bit baffling, i just disconnected it all together :dunno:
     
  14. PaleRider

    PaleRider Registered Member

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    With wide open throttles ported/full vacuum are exactly the same ;)
     
  15. Mad-Dog

    Mad-Dog 1/2 ton status

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    That's strange that you say a carb has no internal (ported) vacuum when you floor it because it mysteriously draws fuel out the float bowls to mix with the incoming air........but I'm sure you have a explanation for that as well.

    If you have air-flow thru the carb then you have ported vacuum.....period
     
  16. Triaged

    Triaged 1/2 ton status

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    Hooked up to ported vacuum you will have nothing (or close to it) at idle, Max just off idle, tapering back down to nothing as you give it more throttle. You will in fact have zero (or close to it) vacuum at full throttle. When people state "total timing" #'s they do not include the vacuum advance.
     
  17. Mad-Dog

    Mad-Dog 1/2 ton status

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    Thanx for the link, it has caused me ponder my train of thought and perhaps realize that i may have been wrong in some of my earlier replies,

    " I am Man enough to admit it"

    On the same note the combination of parts i am using works well for me but may not for someone else....
     
  18. Fierospeeder

    Fierospeeder Banned

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  19. smalltruckbigcid

    smalltruckbigcid 1/2 ton status

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    Full throttle vacuum should not exceed 1.5 inches at WOT or the carb is to small and the motor will run lean at WOT because of excess vacuum signal at the boosters. Second you don't want more than about 38 degrees total timing at any time or you will get part throttle pinging as the timing over advances. Ported vacuum was done as an emissions measure to lean out the motor to help for smog reasons,and heres how you can tell what you have. I f you have a temp sensor on the top of the t'stat hosing and its hooked to 2 vacuum sources and goes to the distibutor on the 3rd vac line follow the 2 source vac lines to their source, those should be 1 ported and 1 manifold. It worked like this, if the engine was cold or at least not very hot it got ported vac timing, but if it got hot it got manifold vac timing to cool the engine down. This is how I hooked up my vacuum advance, got a Crane adjustable unit and set it for a max of 12 degrees and hooked it to manifold vac. Reworked the dizzy and set it for a max of 22 degrees mech advance. Set the total timing at 2500rpm for a max of 36 degrees from both sources. That means I'm setting at 2 degrees base timing, so it starts easy and then idles good as the vacuum advance comes on. This gives me the best part throttle crusing, no surging, and for whatever reason I get a little surge with 38 degrees timing so it stays at 36.
    George
    I'm saving my pennies for a MSD digital box and billet distributor, the timing retard feature for starting is so cool, you can run a locked distributor and still start the engine when its hot. Best of both worlds.
     
  20. bigbadchev84

    bigbadchev84 1/2 ton status

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    Ok so what do i set my timing to with the hose disconected? i will be using full manifold vacuum and my motor is stock with no emissons. i put on an edelbrock 500cfm tuned for performance is what he box said. my quadrajet i got from my buddy was crap and kept loading up.
     

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