Ported vs manifold vacuum advance solved!!!

[Ceedawg]

The thread that never dies

 

[Ranger16]

It should be retitled.
Ported vs Manifold Vacuum - The Debate Continues!!!

 

[biomedtechguy]

The thread that never dies

Oh I've seen this debate in different places on Mopar forums (because Pontiac is the only other forum I've visited, for the wife's GTO) and I am still doing paperwork on a deadline so I haven't read it all, cross-referenced other posts maybe from other threads, even other sites.. across the vast expanse of space and time...LOL.
I have personally wrestled with the ported vs manifold pressure issue because I have a FBO ignition system from Don, and a 6bbl intake too.
FWIW the most awesome ignition system I'm going to, from Progression Ignition, specifically states with emphasis theirs, to:
"h. Connect the vacuum port to a FULL intake manifold vacuum source. DO NOT
use ported vacuum."
That's copied from their installation manual. At least that will be the same connection I'm used to since I've had the FBO system for 5 years or so...

 

[eldubb440]

The thread that never dies

I thought it was the rebody thread

 

[biomedtechguy]

Honestly, I think this is critically important information. Even "experienced" guys may not be as knowledgeable as I believe they could be, but then again, that may be the couple of 10ths that puts me across the finish line ahead of them.
I'm still doing paperwork, but I'm checking in on follow up posts and I'm definitely reading through this thread when I'm done.
It's hard to find an enthusiastic audience for gung ho car guys, even harder for guys like me who are really into ignition system design.

 

[383man]

Well we know you can use either as long as you set the timing advance up right for what you use. I actually think the real problem is that many just still think ported is not manifold vacuum when it is as its just above the throttle so no vacuum at normal idle speed. There as a discussing on a 6pk website on a FB site and one guy swore they vacuum advance is more the more throttle you gave it and swore its most at full throttle. I tried to tell him how the eng can take 45 to 50 degrees at light part throttle but not a WOT but he did not want to listen to me and many other on the site. Ron

 

[biomedtechguy]

I tried to tell him how the eng can take 45 to 50 degrees at light part throttle but not a WOT but he did not want to listen to me and many other on the site.

I would guess that much advance at WOT would be a quickly learned lesson that that is a "no-no" hopefully without melted electrodes or worse.

 

[Jeff Erwin]

OK, newby (to this conversation) question. My 440x6 has the vacuum port on the distributor plugged. I am replacing the distributor, so this conversation suddenly becomes relevant. Question: Do I set the advance with the vacuum connected or disconnected?

 

[turbine68rt]

Set it with the hose removed and plugged until you are satisfied with the initial setting then reconnect.

 

[Jeff Erwin]

Set it with the hose removed and plugged until you are satisfied with the initial setting then reconnect.

Thanks.

 

[1STMP]

Late to the party as usual.
Vacuum advance is distributor diaphragm
dependent/ designated. That's why there
are debates all over the map on this issue.
After all, it's the distributor that delivers
the required advance.
I run a pro billet distributor from 440 source.
(ignition inclusive), and install instructions
clearly state ported vacuum. Follow what
is recommended via your distributor
manufacturer. Just my .02.

 

[biomedtechguy]

Follow what
is recommended via your DISTRIBUTOR manufacturer.

100% agree! It is the distributor that is affected by the vacuum source, and just as Don at 4 seconds flat aka FBO Ignition Systems recommends...scratch that, INSISTS on manifold vacuum be connected to his distributor setups, as does my next ignition system from Progression Ignition. (calling Progression Ignition today w/a few questions, and fully expect to place my long awaited order)

 

[whayden2003]

So I’m going to throw this in here to just get laughed at. I plug the vacuum advance. Use FBO timing limiters. Set the base to 20 and set the limit disc on the 14 degree position. 34 total. 383 larger cam. Engine makes the vacuum it needs for the power brakes at idle. Gear reduction starter. Starts fine. With 20 degrees she responds well to idle adjustments way better.

 

[Dragon Slayer]

It is amazing this get so much attention. The ported is just a switch. Keeps vacuum adv off at idle. Once port exposed you're at or near manifold vacuum and vacuum adv now in play. That is it in a nutshell. All based on having stock carburetor, stock distributor and stock initial timing. Which is nowhere near what is normally being used today. Stock Initial depending on year and motor was anything from retarded a few degrees or 0, and 6 to 8 advance, or maybe 12 adv on early performance cars.
Slap in 20 or more initial and use vacuum adv on manifold and now you have a much higher initial unless you set it with vacuum attached. Let alone having a mechanical cam that may add 20 to 30 degree depending on what initial it was made for. I think people get into trouble with a mismatched distributor set up, other than folks using the adjustable mech advance type.

 

[Turboomni]

I plug the vacuum advance. Use FBO timing limiters. Set the base to 20 and set the limit disc on the 14 degree position. 34 total. 383 larger cam. Engine makes the vacuum it needs for the power brakes at idle. Gear reduction starter. Starts fine. With 20 degrees she responds well to idle adjustments way better.

I thought the main reason for vacuum advance is to be able to burn more completely lean mixtures at low load part throttle conditions and needing +40 degrees advance at those times to do so. This is for street cars I believe. I had heard of accelerated engine wear [carbon deposits etc] if I remember correctly if it wasn't used in a street car for any length of time. Correct if I am wrong. I will ask the question then.
What are the specific reasons car manufacturers used vacuum advance?
What happens to engines run on the street that do not run vacuum advance?

 

[biomedtechguy]

I spoke with the owner of Progression Ignition. I'm still getting one, maybe next month. I will have some really good information to share once that happens, and I'll put it in a Progression Ignition thread.

 

[biomedtechguy]

I thought the main reason for vacuum advance is to be able to burn more completely lean mixtures at low load part throttle conditions and needing +40 degrees advance at those times to do so. This is for street cars I believe. I had heard of accelerated engine wear [carbon deposits etc] if I remember correctly if it wasn't used in a street car for any length of time. Correct if I am wrong. I will ask the question then.
What are the specific reasons car manufacturers used vacuum advance?
What happens to engines run on the street that do not run vacuum advance?

Everything you stated as reasons for vacuum advance are true, from my experience and in my opinion too.
If that is correct, you have answered your own questions!

 

[whayden2003]

I thought the main reason for vacuum advance is to be able to burn more completely lean mixtures at low load part throttle conditions and needing +40 degrees advance at those times to do so. This is for street cars I believe. I had heard of accelerated engine wear [carbon deposits etc] if I remember correctly if it wasn't used in a street car for any length of time. Correct if I am wrong. I will ask the question then.
What are the specific reasons car manufacturers used vacuum advance?
What happens to engines run on the street that do not run vacuum advance?

Not sure what happens if you don’t run vacuum advance on a street car. Would love to be educated. I take any and all advice.

 

[Turboomni]

Not sure what happens if you don’t run vacuum advance on a street car. Would love to be educated. I take any and all advice.

I would love to be educated too and see no one laughed at you. I even removed that statement from your quote as many guys run without vacuum advance. There must have been a very good reason for all the car manufacturers to go to the trouble ,hassle and expense to install them on all their cars.

 

[Ceedawg]

I thought the main reason for vacuum advance is to be able to burn more completely lean mixtures at low load part throttle conditions and needing +40 degrees advance at those times to do so. This is for street cars I believe. I had heard of accelerated engine wear [carbon deposits etc] if I remember correctly if it wasn't used in a street car for any length of time. Correct if I am wrong. I will ask the question then.
What are the specific reasons car manufacturers used vacuum advance?
What happens to engines run on the street that do not run vacuum advance?

It’s all about burn time, advancing the timing starts the flame front sooner so it’s hitting the piston coming up to tdc, more of a push, like spring resistance. The expanding pressure wave meets the piston head on, creating more pressure, the wave doesn’t chase the piston down the cylinder