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Confirming the ported vs. manifold vacuum debate


Well-Known Member
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5:48 AM
Nov 26, 2019
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Eagan, MN
So I think have read or watched 20+ articles on the ported vs. manifold distribution advance topic. In conclusion for a 67 R/T 440 4sp with a very mild
hop-up to the engine (aluminum intake, 1-up cam, Edel Performer, stock heads 10:1, stock manifolds, etc.)
1 - earlier AFBs including the original one for this car (which I have) had only a ported vacuum hookup, that must mean something as it was engineered that way
2 - Edelbrock says to hook non-emissions cars (like my 67 R/T) to the manifold vacuum for a 750cfm Performer like on the car currently. It has both outputs.

--> end result, play around with it and see which you like.

Taaa Daaa!

For anyone who cares, I will do some "seat of the pants" testing with different initial timings, and put observations in this thread. Once I solve the current
fuel leak.....
I am subscribed. I get both sides of it but...............
LOL you can use a ported vacuum line on the fuel spill. It wont flood at idle because it only picks up fuel at rpm!:rofl:
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Edelbrock says to hook non-emissions cars (like my 67 R/T) to the manifold vacuum for a 750cfm Performer like on the car currently. It has both outputs.

FF to 4:45. Here they suggest to use ported for advance, and manifold for cars with vac modulators. Personally I use the ported for vac advance, and manifold source for the choke pulloff when I'm using my 1905 AVS2.
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Not to muddy the waters but....
There is the third choice of no vacuum advance. :rofl:as posted above
Mechanical advance only master race checking in.

Not to muddy the waters but....
There is the third choice of no vacuum advance. :rofl:as posted above

If it's basically bone stock, hook it up as per the car manufacturer.
If you want to be a wildman, hook it up like a different car manufacturer.
Vacuum advance? Whats that? How does it work? :lol:
Those that use manifold vacuum to control the distributor are knuckle heads......conversely......those that insist that the ported vacuum advance connection is "the absolutely only way to go" usually based on the seat of the pants comparison methodology and the "you don't need either or NO vacuum connection whatsoever is best" based on the testimonials professed by: my next door neighbor's cousin's sister's husband's uncle's best buddy's friend's down at the local watering hole....only on Tuesdays. The results are demonstrated on his 700 CID/ 900 Hp stroker Ford SOHC FE block engine......he states he can melt the tires off on his pro street ride.....using 100LL ave gas exclusively.......but.....the real answer or method lies with the owner..... just a casual observation......
Frankly, being a tach drive no vacuum distributor user, I don't understand the conundrum. Only two ways, ported or manifold vacuum. Try it both ways, stick with the one that works best for you. DONE! (What is so freakin hard?)

Now, if you're talkin pinion snubbers and pinion angle.......
The problem with this 'debate' is the ignorance that goes along with it......
I could give many examples but here is just one example: Bill Bloggs is using 22* initial timing & then hooks up his VA to manifold vacuum, which adds 25* of timing. His modified dist has the very light springs controlling the centri curve for better throttle response. The engine surges at cruising speed, but didn't before MVA was added. So MVA is no good........
Clearly here the Edel 1411 install manual says to use MVA for "non-emissions controlled engines", i.e. the 440HP in my 67 R/T. Interesting this is opposite to what was said in the above YouTube video.......but then again the pic has to tell you that the PCV port is "not for fuel".... so consider the source.....as such, my testing that will occur over the next couple of weeks.

I take it you haven't seen the picture of the edelbrock carb with the fuel line hooked up to the pcv port. Owner was complaining it ran rich, if I remember.....
Regarding #15's observation reference to "ignorance", remembering the George Orwell's novel "1984" that ignorance is bliss, one could accept the concept....or not. There are just as many "PRO" ways of acceptance as there are "CON" ways of non acceptance......which way is "BEST"????
OP - before you hook it up and test the difference between ported and manifold, be sure to know where your initial timing is set at, your total timing with Vac Advance disconnected, then realize that your Vacuum Advance canister may add too much additional timing at idle/off-idle and need to be shimmed to lower the amount of added advance. Only then will you be able to test which works best for your setup.

Here's a post from the A-bodies site with an excellent photo showing a wire shim inside a mopar adjustable Vacuum Advance can. The wire shim in the photo limits travel in the front to rear direction of travel along the can's internal diaphragm spring. The adjustability of these cans without this shim only allows adjustment of the Vacuum level at which the advance is applied.

Out of all the articles I've read on this debate, few mention the option of shimming the Vac Advance can arm to limit added advance.

From the A-bodies site:
How To Limit and Adjust Chrysler Vacuum Advance Cans
This should muddy the waters more, you can also play around with vacuum delay valves. However the only real way to tell if it helps or hurts is to keep very detail records of changes made and improvements or losses. You can also use a 3 way vacuum connection. These changes like this for a street driven car take a lot of time.
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