Where do you have your vacuum advance hooked up?
#2451287
02/13/18 06:08 PM
02/13/18 06:08 PM
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Posts: 290 Dayton, WA
wesgtx440
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Ported or manifold vacuum.
And if you feel like sharing. Why did you choose one vs the other?
68 Charger R/T 440 auto
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Re: Where do you have your vacuum advance hooked up?
[Re: wesgtx440]
#2451333
02/13/18 07:18 PM
02/13/18 07:18 PM
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BigBlockMopar
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I always prefer manifold. Makes for a cooler running (idling) engine. (And my MegaSquirt ECU wants it there ) On another car with a large(r) cam it's connected to ported, to prevent too much ignition advance fluctuations at idle. IMO, ported is mostly more an emission thing because it helps for a more complete burn and hotter exhaust temps (at idle), although the factory used ported advance for as long as I know. Perhaps they installed it like that for a more steady/stable idle-quality.
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Re: Where do you have your vacuum advance hooked up?
[Re: ahy]
#2451440
02/13/18 11:11 PM
02/13/18 11:11 PM
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Posts: 3,933 Oregon
hooziewhatsit
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As long as your vacuum at idle in gear is higher than the vacuum needed to actuate the vac advance can, you'll have a steady idle. If your vacuum is too low and the can moves, then nothing will ever settle, and you'd be better off using ported vacuum.
I have mine hooked to manifold since I didn't want to take the distributor out to put in the limiting plate, and I wanted more timing at idle.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Where do you have your vacuum advance hooked up?
[Re: wesgtx440]
#2451568
02/14/18 05:58 AM
02/14/18 05:58 AM
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That AMC Guy
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All my junk is mostly stock, so they all run full manifold. Nice smooth idles, no overheating. Good gas mileage and smooth steady cruising.
I can see the guys with modified engines running ported and that's Ok too!
Bloody Mary, Full of Vodka, Blessed art thou among cocktails....
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Re: Where do you have your vacuum advance hooked up?
[Re: That AMC Guy]
#2451661
02/14/18 02:15 PM
02/14/18 02:15 PM
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Joined: Oct 2011
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wesgtx440
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All good stuff, thanks for all the input. So is there a difference in vacuum cans for ported vs manifold vacuum?? Say like a stock points dist. in '70 was hooked to ported vacuum correct? Are the newer distributors ie: mopar performance electronic ones, firecore, FBO, set up with a different advance unit that is designed to use manifold vacuum? or does it basically just boil down to how much vacuum your engine makes at idle and what it prefers timing wise?
68 Charger R/T 440 auto
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Re: Where do you have your vacuum advance hooked up?
[Re: wesgtx440]
#2451662
02/14/18 02:24 PM
02/14/18 02:24 PM
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hooziewhatsit
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All good stuff, thanks for all the input. So is there a difference in vacuum cans for ported vs manifold vacuum?? Say like a stock points dist. in '70 was hooked to ported vacuum correct? Are the newer distributors ie: mopar performance electronic ones, firecore, FBO, set up with a different advance unit that is designed to use manifold vacuum? or does it basically just boil down to how much vacuum your engine makes at idle and what it prefers timing wise? A vacuum can is a vacuum can. The only real differences are how much additional timing they provide, and what vacuum level they start to move at. Most can have the vacuum level changed by using an allen wrench through the nipple to adjust the spring load on the diaphram. (A mity-vac comes in very useful for adjusting this) To adjust the amount of advance a physical stop needs to be added to the arm. Otherwise, it's based on your specific engine's idle vacuum, how much mechanical advance your distributor has, and how much total timing you want.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Where do you have your vacuum advance hooked up?
[Re: wesgtx440]
#2451694
02/14/18 03:56 PM
02/14/18 03:56 PM
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Joined: Aug 2003
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Cab_Burge
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Early GM, Chevys, used manifold vacuum until the early to mid 1960s, Mopar and Ford have always used ported vacuum advance that I'm aware of The major difference in using manifold vacuum advance it is advanced most at idle and then drops off as the vacuum declines to the throttle, ported vacuum doesn't start to work until there is airflow past that port
Last edited by Cab_Burge; 02/14/18 03:57 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Where do you have your vacuum advance hooked up?
[Re: Triggerfish]
#2451745
02/14/18 06:09 PM
02/14/18 06:09 PM
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Joined: Oct 2011
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wesgtx440
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Did you previously run the dual point with no issues?
68 Charger R/T 440 auto
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Re: Where do you have your vacuum advance hooked up?
[Re: wesgtx440]
#2451751
02/14/18 06:18 PM
02/14/18 06:18 PM
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hooziewhatsit
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I guess the way I see it is if you have an engine that starts fine with the static advance setting and it idles good, then ported vacuum is the way to go. If you have an engine that idles good with more advance than allows for starting with out kickback, then manifold vacuum is the better one since you can retard the timing to allow it to start and then have it advance a set # of degrees with the vacuum to where it idles good. So at WOT, both manifold and ported vacuum signal will drop significantly and mechanical advance takes over at that point correct? Sorry for all the questions, just trying to educate myself on this subject Pretty much Some cams like more timing at idle. This raises the idle speed, giving you enough room to close the throttle blades so it will idle on the idle circuit. Some don't. To do this, you can: use ported vacuum crank up the initial timing, and limit the total timing. But, like you mentioned, you might run into kickback issues. Or, use manifold vacuum a more reasonable initial timing (maybe still limiting the total), And have the base timing jump to initial + vac advance once it starts. Once the throttle is open past idle, both manifold and ported are the same. At wot, both are near zero so there is no advance added. The only difference is at idle with the throttle closed.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Where do you have your vacuum advance hooked up?
[Re: wesgtx440]
#2451754
02/14/18 06:22 PM
02/14/18 06:22 PM
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hooziewhatsit
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PIA to get it to stop pinging at WOT. At WOT, there's no vacuum advance, so I would look at the total timing, fuel, or both.
If you ever find yourself in a fair fight, your tactics suck.
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