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Old 07-30-2003, 01:34 PM   #1
redhat778
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Member#: 34184
Join Date: Mar 2003
Location: Atlanta
Vehicle:
02 WRX
Now with STI VII Swap

Default Absolute Pressure VS. Boost Pressure

Little bit confused guys.....tried search but I couldn't come up with anything. How do absolute pressure (MAP) and boost pressure relate. Bottom line here is what I'm trying to do. I just finished my water injection and I was trying to have it come on with spare soleniod w/UTEC and i'm trying to get it to come on when RPM's >3k TPS>70% and boost is greater then 12 psi. Thanks
Michael
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Old 07-30-2003, 01:47 PM   #2
zaxrex
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Default Re: Absolute Pressure VS. Boost Pressure

Quote:
UTEC user's manual - Parameter Constants
MAP Display allows you to select whether you wish to display the absolute pressure relative to 1 atmosphere or gauge pressure. IMPORTANT: This ONLY applies to the logger and dashboard map readings. Load points are always in absolute pressure.
Gauge pressure shows the difference in pressure between the tap point and the local atmospheric pressure. This shows the differential between the two, with the atmospheric pressure variable.

Absolute pressure is the pressure differential between the tap point and 14.7 (14.696) psi or 1ATM. This is a true measurement because you are going against a set standard while the relative pressure flopps around depending on the environment.

Last edited by zaxrex; 07-30-2003 at 02:05 PM.
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Old 07-30-2003, 03:01 PM   #3
SysRq
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Quote:
Originally posted by zaxrex

Absolute pressure is the pressure differential between the tap point and 14.7 (14.696) psi or 1ATM. This is a true measurement because you are going against a set standard while the relative pressure flopps around depending on the environment.
This is the TurboXS definition of absolute pressure which is not technically correct.

Absolute pressure is, well, absolute. Absolute pressure = gauge pressure + ambient pressure. When you run 1 bar of boost under normal atmospheric conditions, your absolute manifold pressure will be close to 30 psi.

What UTEC displays as absolute pressure is really absolute pressure - 14.7psi. What UTEC displays as gauge pressure, is really absolute pressure - ambient pressure (probably obtained from MAP reading with engine off, since UTEC lacks its own pressure sensor).
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