# Vacuum gauge



## gtoearl (Dec 21, 2009)

I purchased a used vacuum gauge for my 66 gto. I hooked it up directly into the intake manifold. It works but it doesn't get in to the green, no matter what rpm. At idle in park it's in the yellow..........Any suggestions.......:seeya


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## geeteeohguy (Feb 2, 2008)

Connect another vacuum gauge to the intake and verify that your old gauge is accurate. If so, and you have low manifold vacuum, it could be due to retarded timing, camshaft design, or other issues.


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## gtoearl (Dec 21, 2009)

thnaks for the reply.......going to put a tri power on in the near future..........just thought that maybe I had it hooked up wrong........I do have a mild cam with a little higher lift. Not sure just how much......


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## BearGFR (Aug 25, 2008)

Could be the cam. Lift generally alone won't affect vacuum much, but increased duration will, especially if it results in more overlap. (Period where both intake and exhaust are open). Does your new vacuum gauge also have a numeric scale on it, or is it just marked with color bands?

Bear


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## gtoearl (Dec 21, 2009)

Here's a pic of the vac gauge I have.........The gauge never reads better than about 10. But mostly during driving conditions it's 8 or less....When I step on the gas a ltttle hard it pins to right............thanks for your help........

On another note bearGFR, I noticed in your pics that you installed roller rockers..........I'm thinking of the same for my 389 bored out to 400 with # 16 1968 heads..........I've already got a tri power coming for it..........What manufacture or type would you recommend? I'm also thinking of just roller tip rockers as I'm not concerned about more horses.........just to have adjustment to valves is my conceern.........


By the way.............DOES ANYBODY KNOW THIS NAME..........Mike Wasson in Brimfield, IL http://www.pontiactripower.com/index.html

He's building a tri power for me.........


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## pontiac (Mar 6, 2011)

or bad gauge. they can be zeroed internally.


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## BearGFR (Aug 25, 2008)

Unless you've got a -really- rowdy cam, 10 is very low. I'm running a moderate solid roller in mine and it makes around 11 or 12 at idle once it's warm. I'd suspect the gauge. You can get a relatively inexpensive one at most big box parts stores that would allow you to compare readings. Where do you have your current gauge connect for a vacuum source?

Bear


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