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Vacuum Advance Pod
https://slantsix.org/forum/viewtopic.php?t=47138		 Page 2 of 3
Author:  supton [ Tue Nov 29, 2011 6:45 pm ]
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That would be me, making the debate... :oops: In my defense, as I read up further on this, I am finding that both methods are used--ported and manifold--depending the setup. [url=http://www.www.corvette-restoration.com%2Fresources%2Ftechnical_papers%2FTiming101.pdf]This[/url] indictates that ported control came about with emissions, yet when I look at the instructions for this this MSD distributor install, they want ported. As I look further (other sites, won't bother linking), it appears most setups are using ported vacuum, and most recommendations are for ported, yet most descriptions of the mechanisms at work describe it as it was manifold vacuum.

It may be there are some factory setups running manifold vacuum, but it appears it's ported. Sorry. :oops:

[Interesting, this link backs up that first link--ported vacuum came about with emissions... here too ]
Author:  ceej [ Tue Nov 29, 2011 7:03 pm ]
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No worries. :D

CJ
Author:  duval67 [ Tue Nov 29, 2011 7:54 pm ]
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I've heard manifold vacuum all in all works out better.

http://www.jeepforum.com/forum/f12/mani ... um-994651/

That article has been referenced on a number of different forums.
I'm gonna try it both ways and see which works out best.

Supton: Thanks for all the parts links, much appreciated!
Author:  Aggressive Ted [ Tue Nov 29, 2011 10:23 pm ]
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Don't go by what you hear.....think about it. You have initial or base timing, plus mechanical timing plus vacuum advance on top of that. You add all three to get your total advance. See the Engine FAQ section, Advance Curve section. There is a plot of mine plus a template so you can plot your own.

If you have an old car with a carburetor, not fuel injected you have to run ported vacuum or the vacuum advance pod will be at maximum advance at idle or at highest vacuum. You don't want that because it will interfere with base timing at idle.

That is why you need to run ported vacuum so it does not engage at idle. Ported vacuum allows a progressive vacuum advance as you increase speed. Some of us run two vacuum gauges and monitor how much the vacuum advance really sees at various speeds. One on the carb's ported vacuum port and one on the intake manifold.
Author:  duval67 [ Wed Nov 30, 2011 7:30 am ]
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You can still just adjust your base timing to work with the advance at idle.
I'm just going to try it myself. You guys appear to be on the ported side of the argument, and there are others who are on the manifold side.
I'm going to personally see which ends up working best for me.
Author:  WagonsRcool [ Thu Dec 01, 2011 9:25 pm ]
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"back in the day" (1970's) many GM cars ran full manifold vac. Instead of 0-10 degrees timing at idle they had 20+ degrees. (While it made for smooth idle, HC emissions were pretty high, a PIA when dealing with state smog inspection)
The driveability problems would arise from the the many badly designed emissions devices, to worn carbs /throttle shaft, to worn ignition parts. since the eng was "riding" on vac advance, any idle glitch could be magnified. (it can be much more unstable if your mechanical advance starts to come in at idle speed)

Manifold vac advance can work, but my money is staying put on chrysler engineering- & ported vac.
Author:  Josh P [ Thu Dec 01, 2011 10:00 pm ]
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Quote:
Under quick, heavy acceleration, my truck stumbles, feels like it might stall, then catches and accelerates normally.
Another vote for accelerator pump.Most carbs normally have an accelerator pump vent adjustment. If the vent is too low I believe the pump shot is too rich (or possibly restricted and weak?) and your engine will stumble. The adjustment is made using the spring on which the accelerator vent disk sits.
Author:  duval67 [ Thu Dec 01, 2011 11:50 pm ]
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Where would I find that spring?
Author:  Reed [ Fri Dec 02, 2011 12:10 am ]
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Whether or not the vacuum advance on the distributor should be connected to a manifold or a ported vacuum source depends on the design of the system. All slant six vacuum advance systems are designed to be used with ported vacuum sources, NOT manifold vacuum. Other manufacturers did use full manifold vacuum at idle, but in those systems the vacuum was used to retard the timing as opposed to advance the timing like slant sixes. I once owned a Ford Pinto where the distributor vacuum advance used ported and manifold vacuum in an odd system with a vacuum nipple on each side of the distributor vacuum advance diaphragm.

The point is that you should hook up the vacuum to the type of dource the system was designed to use. All stock non-lean burn slant six ignitions must be hooked to ported vacuum.
Author:  wjajr [ Fri Dec 02, 2011 6:40 am ]
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Most of the hot links refer to Chevy V8s, small & big block sporting 90 degree architecture, and a marine engine that has nothing in common with a street driven engine; all are unlike our long stroke 120 degree in-line six cylinder engines, and in particular a stationary race engine in a boat. All that yapping about big advance settings, heat migration, blah, blah, blah at idle dose not directly translate to an inline six, however it is pertinent to a V8.

Not too many street driven engines are operated at idle rpm for any length of time. Arguments for a lot of timing advance at idle to lessen inefficient use of combustion heat for a street driven six is moot in my book. For 1500 rpm and above, the normal street driven engine operation range, yes, proper conservation of heat of combustion is very important, and Chrysler timing devices achieve this goal with ported vacuum controlled advance pods.

My 2 cents
Author:  duval67 [ Fri Dec 02, 2011 9:37 am ]
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Yeah, I guess that makes sense.
All right, thanks guys.
Author:  w2-1969dart [ Fri Dec 02, 2011 11:12 am ]
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What if I have no ports on my carb for the ported vacume.Holley 4150 390cfm
Author:  Aggressive Ted [ Fri Dec 02, 2011 11:40 am ]
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Since you have a a racing carb you can install a different metering block or drill your own hole and install a fitting above the throttle plates. Racing carbs are generally used on race cars with limited timing and they do not use a vacuum advance.
Author:  w2-1969dart [ Fri Dec 02, 2011 11:46 am ]
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Quote:
Since you have a a racing carb you can install a different metering block or drill your own hole and install a fitting above the throttle plates. Racing carbs are generally used on race cars with limited timing and they do not use a vacuum advance.
Thanks for that I will look into the drilling mod. I thought this carb would work good having 1 to 1 secondaries and the 4 corner idle plus all the other cool stuff
Author:  Josh P [ Fri Dec 02, 2011 11:54 pm ]
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Quote:
Where would I find that spring?
Assuming the carb is a BBS, wrapped around the accelerator pump plunger. It's sole purpose is to hold the vent disk just slightly above the carb body to allow... ventilation. The plunger usually has 3 settings notched in it which the spring slides into. For my Dart I know the recommended setting is the middle notch, can't say for your truck, but there are only 3 settings so...
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