Vacuum advance help needed - 1 or 2 port, 1 or 2 diaphram, hose routing, etc?

[oz]

Greetings – sorry in advance for the long post…

I am working on finishing up my ’69 302 rebuild and I have gotten to the point where I need to choose and install the distributor. My plan is to use a stock rebuilt unit from National Parts Depot since I practically live next door to one. I will add a Pertronix ignition to eliminate the points and will be using the vacuum advance. I am installing an Edlebrock Performer RPM intake and 600 cfm Edelbrock (Carter) Carburetor also so originality is not a concern.

One problem I have is that the vacuum advance has never worked before and all the hoses were removed and ports plugged by the previous owner. The stock vacuum advance has dual vacuum ports but I have no idea where the hoses go. I would assume that one goes to manifold vacuum (outer one?) but where does the other one go? I also assume that the rebuilt unit will have the dual port advance…. Is it safe to assume that the two port system is some sort of emissions control measure? Do I really need the two port system?

Second concern is – single diaphragm or dual diaphragm – is this the same thing as single port or dual port? NPD has both for my application in rebuilt form. I have no idea which one to use…

Third Issue: I think my car originally had the vacuum tree on the thermostat housing (plugged now) – since I do not care about originality, is there any reason to buy one and install it? I understand it limits the vacuum to the advance for emissions reasons when the engine is cold.

Fourthly, the Edelbrock carburetor has ports for straight vacuum and ‘delayed’ vacuum… supposedly for vacuum advance. Which should I use for my application?

Finally, I bought the 1969 vacuum diagram at NPD but all it shows is heater / AC / cruise control …. I need the actual engine diagram. Can anyone suggest where I can find this (or describe in detail where each port on the vacuum advance go)? I have the service manuals but I have found nothing.

THANKS!!!!!!!!!!!!

 

[KillerKittyCat]

Your distibutor vacuum advance comes off the carb (delayed). As for the distributor??? If you go to, say, an MSD ignition setup, with the Pertronix it probably will not matter more than price.

 

[10secgoal]

It all depends. Sometimes you go off the manifold vacuum if you need help with idle quality. You won't know until you get it. I wouldn't get a petronix though. They are nice until your alt. goes out and that burns out your petronix. Happened to me 6 months after I bought it. I would say either get a MSD ready to run, or a stock magnetic pick-up from autozone for like 30 or 40 bucks and throw on a MSD 6a box. You'll be much happier with either of those.

 

[86T-Top]

Since you are already replacing your distributor, don't get a points set up and then put a petronix unit in it. Instead a get a distributor from a 302 ford that used a Duraspark 2 box, these have a magnetic pickup in there and no points. Then get a MSD box or you could use a Duraspark 2 box to run the ignition. I also ran a edelbrock carb, and used the vacuum ports of the front of the card to run the vaccum advance. I think it was the delayed vacuum that I used and I plugged the manifold vacuum.

Mario

 

[oz]

Thanks for the replies. Those are good suggestions about the duraspark or MSD setup. My only reservation is that I don't want to clutter up the engine bay with a bunch of boxes, etc.... And I was thinking that the Pertronix had a decent warranty (?)

Anybody have a feeling for 1 diaphram or 2 diaphram vacuum advance? I finally found an illustration showing what each port goes to... one went to the manifold and the other went to the carb. I'm guessing that the one that retards timing is actuated when the throttle is closed quickly(?)
I am leaning toward just getting a single diaphram unit and keeping it simple.

Can anybody explain how the 'delayed' vacuum works? Does it delay the onset of vacuum?

Thanks!