Vaccum Gauges

[Larry 67]

What exactly doe's a vacuum gauge tell you. I've been told if you know how to read, and understand them, they will give alot of info about the condition of your engine, other than a vaccum leak.
Besides looking cool on the console, what are all of it's functions. I will be installing it in a 67 GTO 400, 4barrel, 400TH dual gate.
This car is being restored for cruising on the street, I don't plan to race it at the track.
Thanks for any info you experienced guys can pass along. Take care. Larry

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Cruise On

[Larry 67]

What exactly doe's a vacuum gauge tell you. I've been told if you know how to read, and understand them, they will give alot of info about the condition of your engine, other than a vaccum leak.
Besides looking cool on the console, what are all of it's functions. I will be installing it in a 67 GTO 400, 4barrel, 400TH dual gate.
This car is being restored for cruising on the street, I don't plan to race it at the track.
Thanks for any info you experienced guys can pass along. Take care. Larry

------------------
Cruise On

[Blackcat]

A vacuum gauge tells you how hard your engine is working. Green means light loads or good mileage. Yellow moderate work or poor mileage. Red Hard work and no mileage.
The harder on the gas the poorer the mileage. When you put the pedal to the floor. The gauge will drop to the bottom of the red.

[mike nixon]

if the guage fluctuates alot [ with a smooth idle cam] it can mean burnt or tight valves, retarded timing ect. they are also used to set idle mixture. mike

[Ccass]

Since we are on the subject of Vacuum gauges, who has a 64-67 GTO that they "KNOW" came with this option? For years we have been puzzled as to whether the gauge got a chrome adapter for the console. We know for sure the 65 Big Car had this adapter, but there is no part number in the parts books for the GTO, yet most ask for this adapter when installing a Vacuum gauge.

[Blackcat]

The vaccum gauge was a Dealer installed option. An old Friend Who worked at a Pontiac dealer told me. Lots of people liked the Grand Prix look. So to sell a car they would Gladly install the vaccum gauge for the buyer. (for a small fee)

[Larry 67]

Thanks Guys for the reponses. A friend at work brought in an article from the Jan 74 Hot Rod mag. It's titled What Do All Those Instruments Mean, and really covers the vacuum gauge well. The bracket mentioned that was used in the GP installation...can the same one be used on my Goat console??? If so where can I obtain one..are they a reproduction, or do I look for an original?
If anyone is interested in the Hot Rod article I mentioned let me know. Thanks again...and take care.

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Cruise On

[Blackcat]

Larry, The bracket mentioned is from a 62 Big car. GP, Cat, Bonnie. You will have to drill 3 holes. One large and two small. Follow the pattern on the console backside. the gauge will work without the bracket. It just won't look as good.

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Mr. Z

[Ccass]

We reproduced that bracket way back in 1986. It is our part # PYU300. $24.00 In the parts books it is listed as a 1965 fullsize only "adapter".
http://performanceyears.com/ponor4.htm

[analytical]

I'd like that article please.

[Rugratman]

Being a rookie to the vacume gauge, How did they hook up to the engine, just a small hose from the manifold to the gauge?

If I did not want to mount the gauge to the console, can you check the vacume with a hand held gauge? Should I have done that anyway?

[mike nixon]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by rugratman:
Being a rookie to the vacume gauge, How did they hook up to the engine, just a small hose from the manifold to the gauge?

If I did not want to mount the gauge to the console, can you check the vacume with a hand held gauge? Should I have done that anyway? </div></BLOCKQUOTE>

yes manifold vaccum is what is supplied to the guage.

and yes a handheld unit does the same thing, just not a pretty.

mike

[ctgross]

Wow, talk'n about digging up bones, just realized this post started in 2000! I'd like a copy of the article too, if he can still find it. Got one of those gauges on my 66, but I didn't use the small mount because I'd read that they were only used on the big cars.

[george kujanski]

To add some info: A vacuum gauge is connected to manifold vacuum & can tell you quite a few things about the engine.

First, A stock engine should have about 18 in. of vacuum (actually measured in in. of mercury). A much lower figure indicates probable vacuum leak.

A pointer that drops in reading periodically may indicate a stuck open intake valve or several bad valves.

As mentioned above, the OEM type of gauge had a red/green scale, the green corresponds to the high readings which occur at idle and part throttle conditions. The deeper you get into the accelerator or load the engine, the vacuum goes down (red) showing poor economy.

A typical use during tune ups is when adjusting the idle mix screws on a carb. The best idle is usually at highest idle vacuum.

In modern cars, a vacuum gauge of sorts is built into the system, it's called a MAP sensor, (manifold absolute pressure). It gives the computer a output voltage from 0 to 5 volts, indicating manifold vacuum.

George

[Bill H]

Vacuum tuning info.

http://www.centuryperformance.com/vacuum.asp

[ctgross]

Bill H., thanks, that's a great link!

[6t7gto]

bill h.
thanks for the link.
i just picked up a vac gauge to tune my lemans and needed to refresh my memory.
david

[Brian D'Amico]

Is there a certain place on the manifold that tie into?? I have a Vacuum gauge next to my Temp and oil pressure gauges. I have a Pontiac performer intake. Please let me know where I should run a hose from... Thanks!!!

[TopdownloGTO]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">

First, A stock engine should have about 18 in. of vacuum (actually measured in in. of mercury). A much lower figure indicates probable vacuum leak.


George </div></BLOCKQUOTE>

George, is this condition at idle?

[george kujanski]

Yep. As mentioned in the link above for stock cammed engines. Substantially lower could indicate a vacuum leak. Also as mentioned above low idle vacuum could also cause your power enrichening circuit in the carb to respond, causing more issues.

You should try to maximize the vacuum by adjusting the idle mix screws, adjust the idle speed to the proper value, And then note the vacuum for your engine. That'll be your baseline.

Vacuum will go lower when the engine is under load, and go higher when coasting (throttle being closed).

George