Setting Timing and adjusting vacuum advance canister?

[91r/t]

I did the timing settings yesterday....man it runs great!!! I set the intial at 18 degrees without the vacuum and I have the plate adjusted in the distributor to 16 degrees so that puts my total at 34. Then I hooked up my vacuum advance to manifold vacuum and dialed in the can to give me roughly 10 degrees of vacuum advance as well so that put me at 28 degrees at idle......WHAT A DIFFERENCE. Runs snappy, no header glowing anymore, and seems to burn alot cleaner as well. I am going to leave it there until spring when I can take it for a ride, but I am confident it will run better. I had it running at 2000 rpm for a good amount of time burping the cooling system of air with the cap off and headers were not glowing like last time. I think that answers my intial timing and hot starting issues for sure! Thanks again Don and lewtot184! Getting very close to perfection! Next is a dyno run to see where my a/f ratio is throughout the power band come spring.

 

[Don Gould]

Your Honor, I rest my case and pass the witness.

 

[65-440]

Read this .... http://www.forabodiesonly.com/mopar/threads/plugging-timed-vacuum-advance-hose.398471/

 

[91r/t]

Read this .... http://www.forabodiesonly.com/mopar/threads/plugging-timed-vacuum-advance-hose.398471/

Yea, I have seen that one as I am a member there too. Thanks for the info though! Basically it comes down to your timing needs and cam size. My cam is rather large, and with the big stroker, it wants ALOT of timing at idle/slow speed cruising. Hard to start though when its locked in at 28 initial mechanically when its hot and the starter binds. That's why I am utilizing the vacuum canister at idle to get the timing I need once the car is running.

 

[91r/t]

Your Honor, I rest my case and pass the witness.

Here is a question I always wondered. I don't have a vacuum gauge that I can drive with down the road. Is my motor going to make max vacuum at idle or driving at cruise? I pull 12ish in./mg. at idle and I was under the impression that it won't pull any more when driving. it will float between that and near zero at WOT. This is because the throttle blades near closed will create the most vacuum in the engine. Am I correct in this assumption?

 

[65-440]

It will make more vacuum while steady cruising than at idle ... my 383 idles@14" and at 65 pulls 19" .... my 340 idles at 11" and pulls more while cruising also ... I also use full manifold vacuum for my advance cans with no driveability issues ....

 

[62 Dart Convertible]

Great thread, thanks to all those that were involved!

 

[91r/t]

I love being a test dummy! Anytime! So much more crap to figure out when you have a highly modified engine. Now I know why my dad for years left his **** stock. Runs sweet and less to screw with. There is something to be said about that sometimes.

 

[68 Sport Satellite]

Your correct that's what the vacuum can is supposed to do...Pull timing at idle and part throttle cruise.
The adjustment feature only adjusts the sensitivity of the diaphragm and not the stroke. you need to try and get the can set so at idle it will pull the timing up to about 28-32* pulling from a constant manifold source. If the stroke is too long it will go into a lean miss so you may have to limit the amount of the stroke.... We need to do this on almost every performance application.
Once you get the distributor set up correctly your black plugs and rich idle will go away.

Hi Don,

I see that now on the FBO site you offer separate adjustable vacuum advance cans. It says 10-20 degrees advance. I know the vacuum rate is adjustable, but does this 10-20 degrees mean that these cans you are offering also allow adjustment of added vacuum advance? I was going to just add some .031" diameter wire to my existing adjustable rate can, but would like to hear more about these adjustable cans on the FBO site. Thanks.

 

[68 Sport Satellite]

Is FBO Don still around? Looks like he hasn't been seen on FBBO since 2018. I emailed his FBO site about his adjustable vacuum advance cans and didn't get a response back.

 

[Geoff 2]

Don't know what he charges but you can buy a complete dist from Summit quite cheaply that has adj VA unit.

 

[68 Sport Satellite]

Don't know what he charges but you can buy a complete dist from Summit quite cheaply that has adj VA unit.

Thanks. Let me clarify - I already have an adjustable vacuum advance unit built into my Firecore electronic distributor, but it only allows adjustment of the Vacuum level at which the advance starts. The FBO offered advances indicate adjustment of this vacuum start level as well as a range of advance degrees itself (10-20), so I was just trying to confirm if his units have a built in shim or some other means of adding various shims to limit the advance. I've seen others accomplish this by using different diameter wires (.008" to .031" diameter) as a shim and wrapping around the inside rectangular stop. If I don't shim it up, it gives too much advance and pings, so I'm running without the advance now, but need to shim it and test again. Just trying to avoid multiple distributor remove and replace if possible.

 

[Geoff 2]

The adj VA units typically operate the way you describe. Allen Key adjusts the rate. Some form of stop/limit that is external needs to be fabricated to change or limit the total amount of VA added.

 

[68 Sport Satellite]

The adj VA units typically operate the way you describe. Allen Key adjusts the rate. Some form of stop/limit that is external needs to be fabricated to change or limit the total amount of VA added.

agreed. I have not yet found anyone who has done this, but I have seen some add an internal wire shim. External would be nice to allow adjustment, but not sure it's possible.

 

[68 Sport Satellite]

From the A-bodies site:
How To Limit and Adjust Chrysler Vacuum Advance Cans

I just measured a small paper clip and it's .036" diameter, so roughly based off the graph in this thread, I might expect this paper clip wire shim to reduce vac advance added timing by about 9 degrees from around 22, providing 13 added vacuum advance degrees. My initial is set at 15 degrees and the max total my motor can run without detonation is 32, so with this added shim, I could get an off-idle advance of 28 degrees and this might just be the ticket to allow me to run vacuum advance. Will need to pull the distributor and experiment.

 

[Geoff 2]

68,
You are doing EXACTLY what is needed to dial in MVA. It amazes me that people think they can just bolt on a VA unit & 'all is well'. When they put the new Holley on, they take the time to tune/jet it. But not ign....

 

[68 Sport Satellite]

68,
You are doing EXACTLY what is needed to dial in MVA. It amazes me that people think they can just bolt on a VA unit & 'all is well'. When they put the new Holley on, they take the time to tune/jet it. But not ign....

Yeah, it took me a while for it all to click in my head - I used to think the adjustment in the can adjusted the amount of advance and didn't realize until later after much reading and visiting the dyno shop that it only adjusted the vacuum level at which it starts.