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Gauge - Vacc/Boost vs. boost

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Old Feb 7, 2005 | 04:03 PM
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Gauge - Vacc/Boost vs. boost

I saw that Autometer makes a Vacc/Boost gauge, and just a Boost gauge.
What are the differences between them? What does the vacc side show you?

Which is more desirable on a turbo car?
Can one of these gauges be used for any purpose on an N/A car?

Thanks,
-a

Please restrain from immature responses regarding: a) autometer quality, and b) the reason fr putting a vacc/boost gauge on an N/A.
Thanks
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Old Feb 7, 2005 | 05:29 PM
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NA cars will read just above -14.7 psi with the throttle closed, and 0 psi at WOT. since there's no turbo raising the pressure, it will never read above 0 psi.

a turbo car will read just above -14.7 psi with the throttle closed, and whatever it's boosting at WOT.

being able to see vac is helpful for knowing if there's a vacuum leak. also nice to know it if you have your safc reading pressure instead of throttle
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Old Feb 7, 2005 | 05:48 PM
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I'm not a fan of autometer's stuff, check out VDO.

I opted for a boost only gauge (vdo) and in hindsight I wish I had gotten the vac/boost unit. It would be nice to have an accurate vac reading too.
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Old Feb 8, 2005 | 09:24 AM
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How would you wire a vacc/boost gauge on an N/A? Tap into the pressure sensor tube?
-a
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Old Feb 24, 2005 | 06:40 PM
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any vacuum hose on the intake manifold after the throttle body should be okay
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Old Feb 25, 2005 | 01:02 AM
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Originally Posted by sunshine
I saw that Autometer makes a Vacc/Boost gauge, and just a Boost gauge.
What are the differences between them?
One shows boost and vacuum, the other shows just vacuum. Seems obvious...

What does the vacc side show you?
Post-throttle manifold vacuum.

Which is more desirable on a turbo car?
Desire has nothing to do with it. If you mean which is more useful, then the one that can read both will always be more useful.

Can one of these gauges be used for any purpose on an N/A car?
A vac/boost gauge would be half useless; a boost-only gauge would be completely useless. You use a vacuum gauge on NA engines.
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Old Feb 25, 2005 | 01:13 AM
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Originally Posted by drewl
NA cars will read just above -14.7 psi with the throttle closed, and 0 psi at WOT. since there's no turbo raising the pressure, it will never read above 0 psi.

a turbo car will read just above -14.7 psi with the throttle closed, and whatever it's boosting at WOT.

being able to see vac is helpful for knowing if there's a vacuum leak. also nice to know it if you have your safc reading pressure instead of throttle


uhhh... no
it will read more than 14.7 at idle...
14.7 has nothing to do with it
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Old Feb 25, 2005 | 01:29 AM
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Actually 14.7psi is atmospheric pressure, so it does have something to do with it. But he's still wrong.

With the throttle closed, manifold vacuum will vary according to engine rpm. It'll be 14-18inHg (7-9psi) at idle and 20-22inHg (10-11psi) at higher revs (i.e. decel).
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