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Location:
Liverpool
Registered:
February 2005
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Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 05:04
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I've got a boost gauge in the RA28 plus I've got a spare that came in a box of bits. The first one reads from negative 100 through to 150 kPa. The other one reads from 0 to 700 kPa.
My question is.....WHAT DOES IT ALL MEAN????
The first one's needle indicates from the negative numbers through to the positive numbers depending on how much I accelerate (obviously). The second one (which I tried today) sits on zero and won't move till the boost is up.
Why is there a difference in the calibrations (is that the right word?) of the two? Which is betterer?
They are both VDO gauges.
Please excuse my ignorance on these matters.
Cheers, Greg.
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 05:33
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What you have here are a pair of relative pressuge guages, with differing pressure ranges.
The one which shows a negative thru to positive range, allows the guage to show manifold VACUUM as well as manifold PRESSURE (relative to atmospheric pressure). To me this is the better type to use, as it gives good idications of how your engine is behaving in off-boost conditions, and can help identify manifold leaks should they appear.
The other guage is a positive relative pressure guage, showing only pressure ABOVE atmospheric pressure (aka, BOOST). This means that unless your turbo is pushing through enough air to increase manifold pressure above atmospheric pressure, the guage will not register any reading.
Most likely, due to the range, this guage is intended for very high boost engines in race use, or possibly not even for small engines at all!!
700kPa = ~7.0bar or 102.9psi!!!
150kPa = 1.5bar or around 22psi - this makes much more sense to use!!
i hope this helps matey 
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Location:
Terrigal
Registered:
May 2002
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Location:
Wollongong
Registered:
November 2004
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 05:36
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The boost guage that reads into the negative is a boost/vacuum guage...
They are good...
They allow you to know what the pressure is compared to the air...
The needle will read into the negative in Hg/cm^3 where as boost is measured in kPA...
The second one can not read vacuum...
The one that reads vacuum I'd find better as you can see when boost is about to hit...
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Location:
Canberra
Registered:
January 2004
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 05:47
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a gauge that reads 102.9psi?
DANGER TO TEH MANIFOLD!!!1!11
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 05:49
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kyosho,
it is not necessarily so that his guage reads mercury levels as the units of vacuum.
mmHg is simply another unit of pressure measurement. It is very common so see mmHg on boost/vacuum guages as this is the industry standard for manifold vacuum measurements.
Personally i think pressure guages should all be reading absolute pressure......
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Location:
Liverpool
Registered:
February 2005
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 05:51
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Great stuff you blokes. Much appreciated. I knew I came to the right place for info.
Cheers, Greg
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Location:
Sydney
Registered:
April 2004
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Location:
Wollongong
Registered:
November 2004
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 07:01
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| THE WITZL wrote on Wed, 09 March 2005 16:49 |
kyosho,
it is not necessarily so that his guage reads mercury levels as the units of vacuum.
mmHg is simply another unit of pressure measurement. It is very common so see mmHg on boost/vacuum guages as this is the industry standard for manifold vacuum measurements.
Personally i think pressure guages should all be reading absolute pressure......
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The mmHg is GENERALLY used as it gives a greater MOVEMENT on the needle then what kPA would...
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Location:
cambo
Registered:
May 2002
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 10:33
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yeah i dont think you would want an absolute pressure gauge in a car, no point, just adds confusion.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 11:15
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| THE WITZL wrote on Wed, 09 March 2005 16:49 |
Personally i think pressure guages should all be reading absolute pressure......
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i totally agree... if you are tuning an EFI system, usign absolute pressure make a whole mot more sense from the fuelling calculation side.
i would much prefer to have an absolute pressure gauge 
as for mmhg.. US archaic dinosaur units. SI is the way to go 
and the total needle movement depends on what the gauge is rated to, not the units it measure in (ie an oil pressure gauge reading to 80psi or 5.4bar is the same)
the problem is that people have been conditioned to use certain units and find it hard to adapt. PSI boost has much better bragging rights than KPA boost heh heh
i do find it confusing when ppl say they have 25kpa at idle, as opposed to 75kpa absolute...
Cya, Stewart
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Location:
Campbelltown, NSW
Registered:
November 2004
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 11:23
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Hey All,
i just wish i had a car that required a boost gauge 
that would be soo cool  ive been trying to save up for a new car..somethign with power bu its just not happening...
stupid apprentice wages
/rant
NOLAN
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Location:
cambo
Registered:
May 2002
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Re: Boost gauges. Please educate an ignorant old man.
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Wed, 09 March 2005 11:26
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bah, most gauges for automotive are in/Hg, so get a boost gauge with in/Hg and psi, does the job 
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