# Pontiac Vacumn Gauge hookup -ported vs manifold



## Jetzster (Jan 18, 2020)

I have a Original Pontiac O-30” vacumn gauge on a ‘64 console that appears Teed off the Rear throttle base of the center TriPower carb ,the other side of the ‘T’ goes to The Dist

Not sure if this is this is a “ported “ vacumn, or it’s a manifold vacumn at the carbs throttle base?

So Which type of vacumn port Should a vacumn gauge be connected to for Any meaningful Engine diagnosis? could it be used in either type of port? If so how would the readings differ on troubleshooting the engine?

Ported vs Manifold vacumns appear to work Somewhat opposite of each other, correct? 

I’m seeing about 18”-20” of steady vacumn at idle on the gauge inside which would appear normal , but shouldn’t there also be 0” Vacumn going to the Dist at idle so as to not operate the Advance? Or do I want Full 18” manifold idle vacumn going directly to the Distributer when idleing? 
Seems I read there’s confusion with others often hooking up Their distributors to a manifold vacumn or a ported One, any advice if The Vacumn hookup is correct would be helpful, thx


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## GTOJUNIOR (Aug 7, 2011)

Factory shows Ported off Carb Base. 
So it sounds like you're in a good location.

On my '66 I chose to "T" off the existing hose from the man to my AC controls, this hose also is used to control the Idle "Speed-Up" Switch for my AC.
The gauge has functioned perfectly now for years.


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## O52 (Jan 27, 2019)

Your vacuum gauge is connected correctly. It should have full manifold vacuum at the carb base or directly from the manifold. 
Depending on the engine and year of manufacture, the distributor could have ported or full manifold vacuum. Most but not all pre-smog vehicles run manifold vacuum to the distributor. Factory timing takes this into account and normally requires that you disconnect and plug the vacuum line to the distributor when setting timing. As more and more smog equipment were added to the engines, manufacturers required ported vacuum for emission control. 
Ported vacuum is vacuum ( or lack of) above the throttle plates. Once the throttle is opened there is virtually no difference between the two.


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## Jetzster (Jan 18, 2020)

Thx Junior & O52, glad to know it’s correct,
and I dont have to change anything, just need now to learn the tricks on deciphering vac needle movements,
I Teed a “motor-minder” Greenline vacumn gauge under-dash to compare alongside the OEM vacumn gauge to check its accuracy, and they both do track each other almost identical, just the newer Greenline is understandably faster. Seems a lot can be gleaned from vacumn gauges when one knows how to really understand them...


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## PontiacJim (Dec 29, 2012)

Jetzster said:


> Thx Junior & O52, glad to know it’s correct,
> and I dont have to change anything, just need now to learn the tricks on deciphering
> the needle movements,
> I “Teed” a “motor-minder” Greenline vacumn gauge under-dash to compare alongside the OEM vacumn gauge to check its accuracy, and they both do track each other almost identical, just the newer Greenline is a tad faster.
> ...



All you need to understand is that if that needle doesn't spend most of its time at "0", then you are not using the car correctly.


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## O52 (Jan 27, 2019)

LOL Jim


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## Old Man Taylor (May 9, 2011)

By the way, there's no ported vacuum on a '64 tri-power GTO. The California cars had it on the '66 tri-power. It comes out of the middle of the center carburetor.


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## Jetzster (Jan 18, 2020)

Thx, Roger that, OMT, one great lookin ‘64 btw!


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