Intake vacuum measure
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Joined: Apr 2000
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From: Acapulco Guerrero
Intake vacuum measure
Hi,
i recently replace the intake manifold.
Icant found vacuum leaks or vacuum leaks at hoses, seem to be find
I also installed a mild cam
I dont measure the intake vacuum before i change this parts
Some people says that needs to be near 15
I have 10
Haynes manual says at least 10
At this moment im living at 7200 feet altitude
We know that atmosferic pressure is less at high altitude than sea level
Question
The vacuum is less too or is not the same ?
i recently replace the intake manifold.
Icant found vacuum leaks or vacuum leaks at hoses, seem to be find
I also installed a mild cam
I dont measure the intake vacuum before i change this parts
Some people says that needs to be near 15
I have 10
Haynes manual says at least 10
At this moment im living at 7200 feet altitude
We know that atmosferic pressure is less at high altitude than sea level
Question
The vacuum is less too or is not the same ?
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
While I'm no atmospheric engineer, I can't see why the engine would have different vacuum values? Your piston "pull" would remain the same and create the same internal (inside the intake) vacuum as any other place on the planet.
Now, the "mild cam" is a different question. Cams tend to make the engine idle rougher as the valve timing change is designed to be more efficient (more powerful) at a higher RPM band.
10 seems low to me, but that is me.
Now, the "mild cam" is a different question. Cams tend to make the engine idle rougher as the valve timing change is designed to be more efficient (more powerful) at a higher RPM band.
10 seems low to me, but that is me.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
As you know, your vacuum gauge will read zero at sea level, too!
The technical term for psi (pounds per square inch) is really psi-g (psi gauge). That means the gauge you are using is referenced to the atmospheric pressure at that location.
So, 10 inches vacuum at altitude is the same as 10 inches vacuum at sea lever, because that is referenced to the air pressure at that location (psi-g).
The reason the potato chips bag gets puffed up is measured in psi-a (absolute). Psi-a at sea level is about 14.7 psi-a, and at 7,200 ft., it's about 11.2 psi-a.
Here's an interesting chart:
www.avs.org/AVS/files/c7/c7edaedb-95b2-438f-adfb-36de54f87b9e.pdf
Drifting
Joined: Jan 2005
Posts: 1,354
Likes: 325
From: San Antonio Tx
I agree, 10 seems a bit low for that mild a cam . Maybe late ignition timing?
As far as altitude, This is a cut and paste from an automotive technical school website.
When testing manifold vacuum, it’s important to remember that if an engine idles at 22” Hg at sea level, it will idle at about 17” Hg at 5,000’, 14” Hg at 8,000’ and 12” Hg at 10,000’ altitude. Variations from the calculated standard, of course, are the weather conditions, the engine design, and how well the engine management system adjusts spark advance and air/fuel mixture to correspond to a change in barometric pressure.
As far as altitude, This is a cut and paste from an automotive technical school website.
When testing manifold vacuum, it’s important to remember that if an engine idles at 22” Hg at sea level, it will idle at about 17” Hg at 5,000’, 14” Hg at 8,000’ and 12” Hg at 10,000’ altitude. Variations from the calculated standard, of course, are the weather conditions, the engine design, and how well the engine management system adjusts spark advance and air/fuel mixture to correspond to a change in barometric pressure.
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Joined: Apr 2000
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From: Acapulco Guerrero
When testing manifold vacuum, it’s important to remember that if an engine idles at 22” Hg at sea level, it will idle at about 17” Hg at 5,000’, 14” Hg at 8,000’ and 12” Hg at 10,000’ altitude. Variations from the calculated standard, of course, are the weather conditions, the engine design, and how well the engine management system adjusts spark advance and air/fuel mixture to correspond to a change in barometric pressure.
I will check at sea level in a few months
