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Old 01-13-2005, 11:31 PM   #1
apollo
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Default Boost Guage Readout - What do they exactly mean?

Heh, call me a noob (that's why I'm here ), but I dont really understand the readouts on my Omori Boost gauge. Here's my mental lockup:

Below zero, it reads inches per (what is it, mg) of Mercury (inHg). The pin is in this range during idle and most slow-normal acceleration.

Above zero, the gauge reads PSI. The pin is in this range most often during WOT.

The gauge is hooked up to the vacuum line. As far as I can get, is, that when the pin is below zero, there is a vacuum in the line. When it is above zero, or, when the pin begins to climb, pressure is actually being formed in the line. Right?

Basically, what does it mean when the pin is above and below zero, and why use two differnt measurements?
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Old 01-14-2005, 12:07 AM   #2
Odin
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I think you may be confusing Metric units and Standard units. Obviously the negative pressure (or positive) is independent of what units you use. The rest is just a matter of reading the gauge.

i.e. - 1 mile = 1.6 km

It is the same distance, just different units.
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Old 01-14-2005, 12:29 AM   #3
ncarn8
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Yeah u are correct, when the pin is below zero there is a vacuum situation inside the engine, as the throttle plate is closed.In a n/a car , it would stick at 0 at WOT (or thereabouts) as this is the normal atmosphereic pressure of 14.7psi or 1 bar. Above this the engine is seeing positive pressure and the guage reads this accordingly. -29.92 inhg is a perfect vacuum.

Last edited by ncarn8; 01-14-2005 at 12:49 AM.
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Old 01-14-2005, 12:39 AM   #4
speedyHAM
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In a N/A car, the gauge would read negative (relative to atmoshpere) whenever the car is running due to the throttle plate being partway to all the way closed most of the time and restrictions in the intake system.

The reason for different units is this- on a typical low vacuum system the standard engineering units that are used are inches of mercury (or water for better accuracy), whereas in positive pressure applications Psi or Bar are the typical engineering units. There are many different units that can be used, those two are just typical and easy to use over the range of pressure that an engine sees.
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Old 01-14-2005, 01:20 AM   #5
apollo
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So basically, the engine is seeing no actual forced induction until the needle is above zero?
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Old 01-14-2005, 02:42 AM   #6
ncarn8
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yes, there is no boost at or below zero.
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Old 01-14-2005, 04:15 AM   #7
Jesse00
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wow, im confuse here, anyone here speak english?
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Old 01-14-2005, 09:38 AM   #8
dogfrndnew
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Man, you guys really explained that well. I guess the cliff notes would be
below 0 = vacuum = Suck
Above 0 = boost = Thrust
Everyone knows it is more fun to thrust than to suck.

Sorry couldn't help it...
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