DISTRIBUTOR VACUUM ADVANCE PORT

[FJ5 1970 440]

Just noticed that my electronic conversion distributor has a 3/32" allen head inside the vacuum advance port. Feels like it can be turned both ways. So what does this do? Any advantages with adjusting this, that is if it truly is adjustable? Thanks.................

 

[Chryco Psycho]

Turning it counter clock wise reduces the amount of advance that can be added , it will go about 14 turns allowing anything from zero to 14* advance .
In most cases I do not hook up the vacuum advance at all keeping the advance curve as short as possible using an initial timing of 16-18* & a total advance of 36-38 *

 

[Righty Tighty]

Turning it counter clock wise reduces the amount of advance that can be added , it will go about 14 turns allowing anything from zero to 14* advance .
In most cases I do not hook up the vacuum advance at all keeping the advance curve as short as possible using an initial timing of 16-18* & a total advance of 36-38 *

Not meaning to hijack, but do you leave the vacuum advance disconnected even for performance street builds?

 

[Chryco Psycho]

I always leave it disconnected for performance street builds ...

 

[moparleo]

Connect your vacuum advance for street use. It was designed that way at the factory for a reason and they have a lot more experience and money in r & d than any member. Full manual advance is fine for floor board driving at the track but reality driving is different.
The info in the article applies to any size engine. Better gas mileage and less engine wear.
Read the entire article. A good read about Mopar ignition systems.

Gallery: Distributor Recurving for Improved Fuel Economy - Mopar Connection Magazine | A comprehensive daily resource for Mopar enthusiast news, features and the latest Mopar tech

 

[rarefish]

Turning it counter clock wise reduces the amount of advance that can be added , it will go about 14 turns allowing anything from zero to 14* advance .
In most cases I do not hook up the vacuum advance at all keeping the advance curve as short as possible using an initial timing of 16-18* & a total advance of 36-38 *

Actually adjusting the vacuum advance canister allen screw does not change the degrees of vacuum advance. It changes at what inches of mercury vacuum ("hg.) that the advance starts at. You can make the advance start earlier or later by adjusting the spring tension in the canister.

 

[moparleo]

It is explained further in the link I posted #5.

 

[Chryco Psycho]

This what is inside a canister , once the screw is backed out of the 6 sided plate it will butt up against the end of the housing preventing the arm from being pulled no matter how much vacuum you pull with .
With performance builds , even cam swaps using a 112* CL instead of the factory 115 the engine responds better with a shortened timing curve , I have often welded the slots in the mechanical advance to shorten the curve so you can have more timing at idle making the engine respond better , while not over advancing above 2500 RPM .
I have proven this on dynos for years , I have generally worked on Mustang dynos where you can tune at a consistant speed & load not nessisarily just at wide open throttle pull through the power band , adding vacuum advance doing this does not result in gains .

 

[moparleo]

Boy what was Chrysler thinking. Could've saved millions.

 

[DaveBob]

Just noticed that my electronic conversion distributor has a 3/32" allen head inside the vacuum advance port. Feels like it can be turned both ways. So what does this do? Any advantages with adjusting this, that is if it truly is adjustable? Thanks.................

Chryco Psycho is 100% correct that vacuum advance does nothing to increase WOT power. (At WOT, vacuum advance drops to zero anyway, with low vacuum, when properly set up). However, at part throttle with low load and high vacuum, it improves fuel economy, reduces oil contamination, improves part throttle response, and reduces cooling system load. But, other than that, it's worthless.

 

[Chryco Psycho]

I have no dog in this fight , I know from experience what works for me & I will continue to do so & you can do what you have done or you can try different things & test the results for yourself ...
In one of many cases I was cruzing to a car show in a friends 318 Charger , the mileage was not great so while he filled the tank I retuned the engine disconnecting the vacuum advance & increasing the base timing creating a shorter timing curve as a result we gained 6 MPG on that tank of fuel & response was better , so with a longer timing curve using vacuum advance did Not improve mileage at all while keeping a steady RPM at highway speeds , WOT was not involved at all .

 

[DaveBob]

I have no dog in this fight , I know from experience what works for me & I will continue to do so & you can do what you have done or you can try different things & test the results for yourself ...
In one of many cases I was cruzing to a car show in a friends 318 Charger , the mileage was not great so while he filled the tank I retuned the engine disconnecting the vacuum advance & increasing the base timing creating a shorter timing curve as a result we gained 6 MPG on that tank of fuel & response was better , so with a longer timing curve using vacuum advance did Not improve mileage at all while keeping a steady RPM at highway speeds , WOT was not involved at all .

I'm sorry. I was not trying to target you, just reference your comment.