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This is a discussion on Boost Gauge... is This Normal!? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; heres a pic i just took of the gauge sitting at idle...

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    heres a pic i just took of the gauge sitting at idle

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    Quote Originally Posted by Clarkiss View Post

    heres a pic i just took of the gauge sitting at idle
    1. The units are likely inHg
    2. That is a VACUUM GAUGE not a boost gauge. That's essentially useless for your application. Sure it reads + over atmospheric pressure, but look at the gauge ranges: + 20 inHG is only 9.85 PSI. You'll max out the gauge at just a bit over wastegate pressure.
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    Quote Originally Posted by lytlec View Post
    Wait, Vacuum is represented in different units from boost? That's easily one of the most idiotic product design I've ever seen.

    And of course, no units on the dial face. Whoever designed that product should be forcibly retired.
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    You're fine. Nothing wrong with your gauge. I have a prosport and it does the same thing.
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    Quote Originally Posted by zax View Post
    Wait, Vacuum is represented in different units from boost? That's the most idiotic product design I've ever seen.
    That's how the prosport boost gauges are.
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    Quote Originally Posted by lytlec View Post
    That's how the prosport boost gauges are.
    No surprise there. Prosport is also garbage.
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    Quote Originally Posted by zax View Post
    No surprise there. Prosport is also garbage.
    Ha yep. I thought it was the norm though. I'm too cheap to upgrade. I figured once they stop working I'll upgrade them one by one.
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    That (inHg and PSI) is how the SPT gauge is on my WRX as well. You can quickly tell as the scales are different on one side than the other. To be honest the setup always seemed intuitive to me, as I am used to dealing with vacuum in inHg and boost in PSI.

    I do agree that all gauges should have units, mess up your units and your fancy Mars orbiter turns into an Intra Solar System Ballistic Missile. It is kind of hard to see here, but the SPT does have units: http://i.imgur.com/5dTEV.jpg .
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    Quote Originally Posted by zax View Post
    Wait, Vacuum is represented in different units from boost?
    You been drinking early today ?I have never owned a boost gauge that didn't express vacuum in inHg and PSI in boost. In fact expressing vacuum as negative psi is absurd. I have used vacuum gauges in my NA cars for over 25 years and they all read inHg. Unless we are looking at a different pic, the units are expressed on the gauge face.
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    My AEM digi gauge must do the same thing in regards to units of measurement since I'm around 20 at idle.


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    Boost Gauge... is This Normal!?

    A mixed unit gauge with mmHg and PSI is absurd but common... From memory, even the OEM Porsche VDO gauges for the turbo 4cyl motors were mixed unit gauges.

    Why not just use Pa or bar?!

    Anyway, OP, you're reading different units in vacuum vs in boost.
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    Quote Originally Posted by zax View Post
    Wait, Vacuum is represented in different units from boost? That's easily one of the most idiotic product design I've ever seen.

    And of course, no units on the dial face. Whoever designed that product should be forcibly retired.
    I'm surprised someone with a graduate degree in physics has never seen vacuum represented in inHg.
    While agree that the units should be labeled on the gauge face, I've never seen an Imperial unit manifold pressure gauge that didn't use inHg for vacuum and PSI for positive pressure. Both my Prosport and Defi manifold pressure gauges used that notation (both had the units labeled), so brand quality didn't have anything to do with notation.

    That said, the term "boost gauge" applied to these gauges is a misnomer. A true "boost" gauge would only read from 0-XX positive PSI. VDO makes just such a gauge: Boost | By Type | Instruments | VDO Instruments and Accessories

    VDO describes the vacuum/positive pressure gauges as "turbo gauges": Turbo | By Type | Instruments | VDO Instruments and Accessories
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    Quote Originally Posted by Rambo View Post
    I'm surprised someone with a graduate degree in physics has never seen vacuum represented in inHg.
    While agree that the units should be labeled on the gauge face, I've never seen an Imperial unit manifold pressure gauge that didn't use inHg for vacuum and PSI for positive pressure. Both my Prosport and Defi manifold pressure gauges used that notation (both had the units labeled), so brand quality didn't have anything to do with notation.

    That said, the term "boost gauge" applied to these gauges is a misnomer. A true "boost" gauge would only read from 0-XX positive PSI. VDO makes just such a gauge: Boost | By Type | Instruments | VDO Instruments and Accessories

    VDO describes the vacuum/positive pressure gauges as "turbo gauges": Turbo | By Type | Instruments | VDO Instruments and Accessories
    Can't tell if belittling...

    For all intents and purposes, "boost" and "vacuum" are simply measurements of manifold absolute pressure. I would expect measurements of the same quantity to be represented in consistent units. In physics, if unit conversions are not properly obeyed, one can expect to have a bad time. Simplicity is key my friend.

    Of course I've seen units of pressure represented in inHg (more typically Torr), as I've seen units of pressure in PSI. That is no excuse to use units inconsistently, especially without labels.

    My gauge, while represented in Pascals, uses consistent units above (boost) and below (vacuum) atmospheric pressure. This is something I appreciate.
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    Quote Originally Posted by Donkey View Post
    You been drinking early today ?I have never owned a boost gauge that didn't express vacuum in inHg and PSI in boost. In fact expressing vacuum as negative psi is absurd. I have used vacuum gauges in my NA cars for over 25 years and they all read inHg. Unless we are looking at a different pic, the units are expressed on the gauge face.
    Yet another reason I despise the inconsistency of Imperial units.

    We are clearly looking at different pics.

    How is negative PSI any more absurd than negative inHg? Both are merely units of pressure. This is nothing less than carryover from people classically referring to vacuum in inHg vs. Boost in psi.

    I agree with Spiro: multiunits is absurd.
    Last edited by zax; 03-17-2014 at 08:59 PM.
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