Ported or full vacuum?

You trying to start a fight?

LOL I think I'll just use ported!

The one time I used manifold vacuum, it was accidental, I couldn't figure out why my idle speed kept changing all on it's own. No matter what I did it was cycling up and down, I was thinking bad carb or something, till I saw what I did.

Early(pre 1960) GM used manifold, all the Mopars V8 I've seen(1951 and later) had ported vacume advance

I switched from ported to manifold vacuum about five years ago. I purchased a distributor from FBO purposely built for manifold vacuum. My engine cranks at 18 degrees timing, then as soon as it fires, it has 30 degrees timing at idle. All I needed to do is richen up the idle circuit a tad and it idled smooth. This is like having a timing retard setup at startup. It also drops the timing out at shutdown too.

But, my point is that the distributor was setup to run off of manifold vacuum. I need to have at least 12"hg at idle to keep the timing solid at the 30 degree mark. If the vacuum drops below the 12"hg, then the idle jumps around and the distributor will not hold the timing correctly.
I used two other distributors before this unit and they were setup for ported vacuum. I tested as much initial timing as I could and the most that they would take (& still turnover) was 22-24 degrees. I wanted more timing at idle so I decided to try this setup. Once I reset the idle A/F ratio after the install, I have never had an issue with this setup in 5 years.

You have 3 basic timing needs.
1.While you are wide open throttle. 30-35 deg
2.During cranking 5-10
3.During idle and light throttle cruise. 25-45 deg.

You can not achieve 2 AND 3 unless you chose manifold vacuum.

Not true.

https://www.msdperformance.com/products/ignitions/street_and_strip/parts/6530

I tried 18 degrees initial and it quite often kicks back against the starter. I took the shaft from a small block distributor and put it into my 440 distributor. It's the same as the 440 shaft, but I noticed the slots were smaller than the 440 dizzy. They are only about 2/3 as long as the 440 shaft slots. I need to have it checked to see just how much mechanical advance it's got. I have seen vacuum advance canisters with different numbers stamped into the arm. Am I correct in thinking that there are different amounts of advance that can be achieved by changing vacuum canisters?

if your eng likes 18, a way around that is to wire in a normally closed momentary contact switch to the ign & (1) push the button then (2) get it cranking then (3) release the button while it is still cranking. EDIT I would set the initial with the "vac gauge method" then set the total (initial+slots) with can capped to 36 with the FBO plate then work with spring combo then plug in the can to ported & work with it & yes # on can arm X2 is how much it offers & adj the slope with a 3/32 allen wrench. you could then do manifold & retune for it & see which one works the best for you

I should have worded it as you can't have 2 AND 3 with ported on a stock distributer.

Now that MSD box, that's some fine timing control right there.



Elroy, you answered you own question. Your car wants less than 18 to crank, 18 to idle. Your options are MSD or manifold.

I know, I was just being a clown.

You do know that ported vacuum is the same as manifold vacuum once the throttle is opened up a bit.

So whatever you think manifold vacuum will give, ported does as well, just not at idle and if you need 45 degrees of advance at idle then you really need to reconsider your combo.

No I don't see this as you being a clown. This is a great debate and it requires input from both sides.

I see advantages to both set ups and have tried both on many cars. I have even used locked distributers on "race" combos. Big cam, converter, single purpose etc.

What I don't like is tunnel vision. That is to only use ported because some engineer from 1961 decided to run the factory set up as ported. This is quite possibly the same person that decided negative caster is better and we are going to run the entire electrical system through an ammeter gauge.

Mild combinations idle better with big timing, you have better throttle response, higher torque at tip in and most importantly better mileage.

To be specific, not every combo requires ported, manifold or locked. We have even introduced more combinations if you can control timing with a computer.

So many threads about my car runs great at 20, 30 or 40 deg but it will not start. Why limit your idle and light throttle cruise to a timing your starter wants?

This is true that many dont realize. Ported vacum is manifold vacum but its just above the throttle blade so it has no vacum at idle. Many think ported vacum works like venturi vacum but it is not and does not. At part throttle you will have good vacum to the vacum advance with ported vacum if the port is fully uncovered. Most Mopars I worked with over the years used ported vacum. Some during the emission years used a vacum switch to change from ported to intake vacum at idle if the car was starting to over heat as it would advance the timing to help run cooler and speed up the eng fan when it raised the idle as it was done to keep the eng cooler but it only came in effect if the eng was running hot.
I do see some set their eng up either way. Myself I like ported vacum but I set my eng up for ported as I still have alot of timing at idle and give it a little more just off idle and then just the mechanical advance at full throttle. On my 63's eng I have a Mallory race dist that I got for a good price and has no vacum advance. It has full mechanical advance by about 1800 rpm and the car drives great with it. Since it works good for me and I got it real cheap I use it. Ron