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Vacuum advance #2499132
05/22/18 04:56 PM
05/22/18 04:56 PM
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ILLINOIS
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volaredon Offline OP
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volaredon  Offline OP
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Put a 360 together for my son's ramcharger. Engine originally came from a 76 B body. Checked out the distributor and found the vacuum advance can blown. I have a new one on the shelf been here for years. Standard brand I think the PN is a VC168
On the arm that attaches to the advance plate it is stamped 8.5R. the original one said 11.5R. what difference will this make? Distributor otherwise stock as built in 1976, springs, weights and such. Questions about optimum setup to come later

Re: Vacuum advance [Re: volaredon] #2499149
05/22/18 05:43 PM
05/22/18 05:43 PM
Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp Offline
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Eugene, Oregon
That means it can pull up to 11.5 degrees in the distributor at full vacuum, or 23 degrees at the crank.

The old one (before it blew) was pulling 17 degrees at the crank at full vacuum, unless it had an internal hex adjuster and was set to something lower.


1967 Dodge Coronet Deluxe station wagon

1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
Re: Vacuum advance [Re: volaredon] #2499217
05/22/18 09:10 PM
05/22/18 09:10 PM
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Posts: 36,040
Lincoln Nebraska
RapidRobert Offline
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Lincoln Nebraska
You will be fine with this new one. As noted it has 6 deg less adv but it is a non issue right now.


live every 24 hour block of time like it's your last day on earth
Re: Vacuum advance [Re: Secret Chimp] #2499719
05/23/18 10:57 PM
05/23/18 10:57 PM
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ILLINOIS
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volaredon Offline OP
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Originally Posted By Secret Chimp
That means it can pull up to 11.5 degrees in the distributor at full vacuum, or 23 degrees at the crank.

The old one (before it blew) was pulling 17 degrees at the crank at full vacuum, unless it had an internal hex adjuster and was set to something lower.

I think you have this backwards. the old one was the 11.5.

I have seen the allen screw adjuster in the vac nipple on vac advance cans before. what does this adjust? Can I make the 8.5 act like the 11.5?
Does it change the inches of vacuum that it kicks in at? or same amount of degrees of advance, regardless of where the setscrew is adjusted, at a different vac level or RPM or load?

Re: Vacuum advance [Re: volaredon] #2499726
05/23/18 11:06 PM
05/23/18 11:06 PM
Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp Offline
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Secret Chimp  Offline
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Eugene, Oregon
Originally Posted By volaredon
Originally Posted By Secret Chimp
That means it can pull up to 11.5 degrees in the distributor at full vacuum, or 23 degrees at the crank.

The old one (before it blew) was pulling 17 degrees at the crank at full vacuum, unless it had an internal hex adjuster and was set to something lower.

I think you have this backwards. the old one was the 11.5.

I have seen the allen screw adjuster in the vac nipple on vac advance cans before. what does this adjust? Can I make the 8.5 act like the 11.5?
Does it change the inches of vacuum that it kicks in at? or same amount of degrees of advance, regardless of where the setscrew is adjusted, at a different vac level or RPM or load?


The adjuster determines how much vacuum you need to start pulling advance and what the ultimate maximum is. Basically, you are adjusting a vacuum vs spring resistance curve.

You can't make the 8.5 act like the 11.5, but you could squinch an 11.5 down to act kind of like an 8.5.

Whenever I monkey with this stuff, I like referring to this topic:

http://www.dodgecharger.com/forum/index.php?topic=14888.0

It has very good detail and an example table showing changes for going CW vs CCW with an example canister - once you have a Mityvac-type thing and a timing light on the engine, it is pretty quick to figure out your ideal adjustment.

Last edited by Secret Chimp; 05/23/18 11:06 PM.

1967 Dodge Coronet Deluxe station wagon

1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
Re: Vacuum advance [Re: volaredon] #2499789
05/24/18 01:01 AM
05/24/18 01:01 AM
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax Offline
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Originally Posted By volaredon

I have seen the allen screw adjuster in the vac nipple on vac advance cans before. what does this adjust? Can I make the 8.5 act like the 11.5?
Does it change the inches of vacuum that it kicks in at? or same amount of degrees of advance, regardless of where the setscrew is adjusted, at a different vac level or RPM or load?


The answer is maybe.
Of the three variables, the spring rate can not be changed.
The pre-load (allen adjuster) changes the vacuum need for the advance to start.
The maximum advance is limited by the tabs on the arm.

https://www.forabodiesonly.com/mopar/ams/how-to-limit-and-adjust-chrysler-vacuum-advance-cans.183/







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