vacum advance ports open or timed

Absolutely correct! You got it.
That 50-55 is right about what you want for cruise conditions (gives best economy and throttle response)
And yes, you step on it, and the total advance will very rapidly drop back to your initial-plus-centrifugal amount.

what did you end up with at idle???

check it at idle with the port connected and disconnected (and plugged at the carb)

real good info so far. so does the allen screw in the diaphram limit/max vacum or mechanical advance

turning the allen wrench in the vac can makes the can require more vacuum(or less depending on which way your turn the allen wrench) to overcome the spring tension & add advance. The amt of adv(in dist degrees) is stamped on the arm(which is inside the dist when its mounted). You can file the stops to add more adv that the can can provide or use paper clips or something similar to reduce its travel to reduce the amt of advance. & different cans give different amounts of adv that they can add & that # will be stamped on the arm. Vacuum adv is a very good economy aid & should be dialed in AFTER you have your initial & your mechanical curve dialed in.

EV2Cuda,

Can you post the mopar magazine article about running ported vs manifold vacuum? I saw acouple of mopar mags yesterday but couldn't find the article. Thank you.

George

Neither is wrong. Both offer additional advance above the mechanical and initial timing.

The ONLY difference between ported and manifold is you will have advance during idle and light throttle cruise conditions with manifold vacuum. Most engines need more timing at idle and using your starter as the gauge is wrong. You can also close your throttle blades more with more ignition timing at idle.

I've spend 2 years recording tank after tank in my truck. Ported and manifold have no effect on mileage. I'm sure it's better than without but my numbers show no improvement against each other. I did have tighten the carb idle speed screw with ported but had more torque just off idle with manifold. I have a manual trans. Not sure if this would be noticeable in an auto.

just wondering is vacum high or low under a load with rpm around1700. i don't diesel or start hard and like my of idle torque and response cruising. i get spark nock under a load say if i lug it in 3rd or 4th. if i stay on the gas the knock goes away as the r's go up.if i hold 3rd to about 2300 and hit it theres no hesitation and it screams.if i retard the initial it boggy down low. its a relatively stock 440 in my 4x4. any sugestion. if it was my 2 stroke banshee i'd just plug it into my computer and adjust my timing curve. i don't no if a small engine 2 stroke guy should mess with a bb mopar.lol

was wondering if the fast advance kits or springs are worth it in my 4x4 i mainly run down low and don't go over 4000 rpm

that curve needs to be slowed down. What springs are in there now?

not shure what springs. its all stock 76 440 rv motor.the can is stamped 9l the weights are L13. to slow it down could i lighten the weights or use tighter springs? thanx for the help.

tighter springs but 1st did you find out what your total is(vac adv plugged) & revved till it wont advance any higher & see what you have at that point(want 36-38 for a BB) & see what your initial is at idle(also with the vac adv plugged for this even if you are on ported vac). We need to get a baseline before we alter anything

the problem with running manifold vacuum to the advance is that if you have a hefty cam, there is usually a large difference in vacuum between nuetral and drive. and that changes the advance in the distributor which will change the idle A LOT when you drop it in gear.

With a stockish cam, you have 14 or more inches of vacuum in neutral which will bump the vacuum advance up all the way. when you you drop it in gear, you may drop manifold vacuum to 12 or 13 or more so you are still maxed out on the vacuum advance. so no change in idle.

but put a BIG cam in there where you have 8-11 inches in neutral but only 6 or so inches in gear, the low vacuum, most likely pulsing up and down 2 inches, is going to make you idle timing bounce all over the place and cause all sorts of idle problem.

so yes, there IS a problem with using manifold vacuum depending on what you are running