Help setting timing and vac advance

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standup303

standup303

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First timer setting timing up….

Decided to replace my mechanical advance distributor with the vac advance unit below from Jegs. My plan is to adjust the mechanical advance of the distributor to about 20 so I will have 16 initial and 36 total and keep the 2 silver springs so timing is “all in” at 2400 rpm. All with vac advance disconnected.

My understanding for the vac advance setup it to put a vac gauge on the manifold port at idle with the car in gear and say it’s 10 inch. So then I adjust my distributor vac advance can till it’s pulling 10 inch (test it with a Mity Vac) and that’s it? Plug it in?

440
9.2:1
530/530 lift
235/243 103 CL
4.10
Street car

JEGS 40506: Vacuum Advance Electronic Distributor Fits Mopar Big Block 413/426W/440 "RB" & 426 Hemi V8 Engines - JEGS

IMG_0060.jpeg
 
Start by testing what your engine wants for total timing. Don’t assume 34 or 36 or 38 degrees is best, actually go test. Once you have that number adjust the mechanical to get the idle timing where you want it. Then work on the curve, again testing is the key here, not assuming that a specific curve is best (all in at 2400 is pretty quick). The whole time plotting the curve on paper so changes are easy to see and quantify. After all of that hook up the VA. Adjusting the VA is about bringing in cruise timing for mileage but having it drop out quick enough on throttle application so the engine doesn’t rattle.
 
That's going to need a short curve with a lot of initial (idle) advance. I'd start with 20 initial and give it about 14 mechanical for a total of 34. I would turn the vacuum can adjustment all the way counter clockwise to start. This gives the advance the soonest in the vacuum range. If you get no spark knock with the can adjustment like that, leave it. If you do get some spark knock on part throttle acceleration, turn the vacuum advance adjustment two turns in and try again until no spark knock. I bet you won't get any. At that point, you can plot out your curve with the light, but it will probably be so close you won't want to mess with it.
 
standup303 said:
First timer setting timing up….

Decided to replace my mechanical advance distributor with the vac advance unit below from Jegs. My plan is to adjust the mechanical advance of the distributor to about 20 so I will have 16 initial and 36 total and keep the 2 silver springs so timing is “all in” at 2400 rpm. All with vac advance disconnected.

My understanding for the vac advance setup it to put a vac gauge on the manifold port at idle with the car in gear and say it’s 10 inch. So then I adjust my distributor vac advance can till it’s pulling 10 inch (test it with a Mity Vac) and that’s it? Plug it in?

440
9.2:1
530/530 lift
235/243 103 CL
4.10
Street car

JEGS 40506: Vacuum Advance Electronic Distributor Fits Mopar Big Block 413/426W/440 "RB" & 426 Hemi V8 Engines - JEGS

View attachment 1716319714
Click to expand...


I’m going to say it will be totally pissed off if you bring the timing in by 2400. That’s too fast.
 
And why?
Why are you trying to re-invent the wheel?
the car has a 440 and 4.10s, and already has more torque than almost any street car can handle.
>If it has alloy heads, and a tight-Q, it doesn't need more than 32>34 .
>If it has a manual trans, you will not be able to drive it slowly with more than maybe 10/12 idle timing, because the Transfer ports may be too far closed by 16*.
> but if an auto with a 3200 stall or better; Ok, you can then get away with murder
>But good luck running iron heads at Part Throttle at 36*@2400 plus whatever is in the Vcan, up to around 14* or more.
> But, she might cruise ok with 36 plus 14 @65=2400. It's just Not the right way to get 50*, lol.
 
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RustyRatRod said:
I would turn the vacuum can adjustment all the way counter clockwise to start. This gives the advance the soonest in the vacuum range.
Click to expand...

Read elsewhere on this forum:
if the canister has a hex shaped end, the preload can be adjusted by turning an internal screw. This is done by inserting a 3/32" hex key (Allen wrench) into the nipple. Counterclockwise = higher vacuum needed to advance.
Click to expand...
THAT is an excerpt from here:

www.forabodiesonly.com

How To Limit and Adjust Chrysler Vacuum Advance Cans

Mattax submitted a new Article: How to Limit and Adjust Chrysler Vacuum Advance Cans This comes up enough that it seemed worthwhile to create its own thread. Chrysler Style Vacuum Control Canisters (pods) This write up will cover how to adjust two of the three vacuum advance characteristics...
www.forabodiesonly.com www.forabodiesonly.com

I read the first two to be opposite statements. I didn't go look up my spec sheet on the matter, but IIRC, the latter is correct.

...and NOT the same as the former.

Yea, verily or...'YOU! Go Sit In The Back Row!'
 
canyncarvr said:
Read elsewhere on this forum:

THAT is an excerpt from here:

www.forabodiesonly.com

How To Limit and Adjust Chrysler Vacuum Advance Cans

Mattax submitted a new Article: How to Limit and Adjust Chrysler Vacuum Advance Cans This comes up enough that it seemed worthwhile to create its own thread. Chrysler Style Vacuum Control Canisters (pods) This write up will cover how to adjust two of the three vacuum advance characteristics...
www.forabodiesonly.com www.forabodiesonly.com

I read the first two to be opposite statements. I didn't go look up my spec sheet on the matter, but IIRC, the latter is correct.

...and NOT the same as the former.

Yea, verily or...'YOU! Go Sit In The Back Row!'
Click to expand...
Turning the screw counter clockwise removes tension from the spring and allows the vacuum to more easily pull the advance mechanism. Conversely, turning the screw clockwise compresses the spring, making it more difficult and requiring more vacuum to operate the advance. I don't understand any of what you said, but that ^^^^ is how it works. ;)
 
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Nope, turning the Allen Screw CW reduces spring tension, does not increase it. You ALWAYS start with AS would fully CW.
 
303.
You start with idle timing....& finish with the WOT curve.
This is how you do it, & in this order:
- with approx 10-16* init timing, carb idle adjusted as best as you can, engine idling in gear if auto slowly turn dist to advance timing; turn until you get the highest rpm; toggle dist to make sure you have the highest rpm. Then check the timing.....This part of the test is now finished.
- say you got 40* in the test. That is what THIS engine needs for best idle, highest vacuum etc. It can be any combination of init [ static ] + MVA that gives 40*. Some of the Chrys dists only get 22* from the VA unit. GM HEI units give about 30*. A 440 I dialled in some months ago reqd me to adapt the GM VA unit to the Chry dist to get enough MVA at idle.
- so now you know the idle timing reqd, select the combination of init + MVA. Always better to keep the init low & use as much MVA as possible; it reduces the possibility of light throttle pinging.
- now you select the total timing for WOT. If you, say, selected 18* init & want 38* at WOT, then the centri curve needs t be 20*. The actual combination of springs/weights would be any bodies guess & getting that dialled for max HP at various rpm levels could only be found on a dyno.
- if you get light throttle pinging......idling in gear, turn AS 2 turns CCW & check timing. Keep going 2 turns CCW, checking timing each time, until timing moves or becomes unsteady. Then turn AS 3 turns CW.

img287.jpg


img267.jpg
 
I don't understand any of what you said...but you're wrong.

That is not a reasonable approach to anything.

standup303 said:
I adjust my distributor vac advance can till it’s pulling 10 inch (test it with a Mity Vac) and that’s it?
Click to expand...

I don't understand that. Might you mean it's adjusted such that the unit STARTS advancing at a measured 10" of vacuum?

The distributor vacuum advance can doesn't 'pull' inches of Hg. It pulls a rod WITH the application of vacuum to the can. It does advance the spark depending on the amount of vacuum it is attached to and when that advance starts in the vacuum 'curve' (given amount of vacuum at particular RPM) is dependent on the setting of the allen-spring INside the vacuum canister.

Yes, you can check all of that with a Mity Vac..or any vacuum source.
 
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If I may....

Rusty, you got it right from the standpoint of thinking righty-tighty/lefty-loosy and all, but it's NOT the 'bolt' of the contraption that is changing, it's the 'nut'. ...I think.

Of course, it COULD have been a LHT assembly...:eek:

Good pic!
 
canyncarvr said:
If I may....

Rusty, you got it right from the standpoint of thinking righty-tighty/lefty-loosy and all, but it's NOT the 'bolt' of the contraption that is changing, it's the 'nut'. ...I think.

Of course, it COULD have been a LHT assembly...:eek:

Good pic!
Click to expand...
Yeah. It's the nut lookin back at me from the mirror.
 
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