Thank you Mr. Wizzard and for our next subject... ;)
-----Original Message-----
From: Bernd D. Ratsch [mailto:bernd@texas.net]
Sent: Wednesday, November 15, 2000 8:12 PM
To: dakota-truck@buffnet.net
Subject: DML: RE: Re: Holley TB Update - WOW! - Flowbench Testing 101
25" H2O = Ya gotta wear waders to test it. ;)
Ok...seriously, here goes:
Airflow is initiated by a pressure differential. A pressure differential can
be most simply described as a pressure difference between two points.
Pressure, at least as it applies to the automotive field, is normally stated
in psi. (Pounds per square inch), Hg" (Inches of mercury), or H2o" (Inches
of water)
The earliest pressure measurement devices were simple manometers. A
manometer is made up of a clear tube formed into the shape of a U, and
partially filled with liquid. If there is no pressure differential between
the two ends of the tube the liquid will fill both sides of the tube by the
same amount If there is a pressure differential between the two tubes, the
liquid will flow from the high pressure side of the tube to the low pressure
side. The difference of the fluid height between the two sides of the tube
is the pressure differential, stated in inches, millimeters, or whatever
unit of measurement you prefer. If the tube is filled with water, the
pressure drop is stated in inches of water, if it is filled with
mercury...well you get it.
Atmospheric pressure at sea level, at 59 degrees farenheit is 1bar., 14.7
psi, 29.92 inches of mercury, or 406.9 inches of water. This is referred to
as SPST, or standard pressure, standard temperature. From this you can see
the realtionship of these different units of measure.
During the intake stroke the chamber volume increases. Since the mass of the
air in the chamber is the same, but its volume has increased, its density
has decreased, and so then has its pressure. (Remember, air density is
directly proportional to air pressure, and air pressure is directly
proportional to air density.) The result is a pressure drop, or a pressure
differential between the chamber, and the air at barometric pressure outside
of the engine. This initiates air flow into the chamber.
When airflow is measured on the flowbench, it is really the restriction to
airflow that is being measured. If for instance there were no restriction to
airflow, a pressure drop could not be realized. To be able to compare the
airflow of one induction system to another, flowbench testing is usually
done at a standard pressure differential. The most commonly used pressure
drop for flowtesting is is 25 inches of water.
The pressure drop caused by the engine itself is not steady like that of the
flowbench. In fact, the pressure varies a great deal throughout the intake
cycle. (There are, however, many factors that determine the pressure
throughout the cycle.)
Anything else?
- Bernd
-----Original Message-----
From: owner-dakota-truck@buffnet.net
[mailto:owner-dakota-truck@buffnet.net]On Behalf Of Steven St.Laurent
Sent: Wednesday, November 15, 2000 7:02 PM
To: dakota-truck@buffnet.net
Subject: DML: RE: RE: Re: Holley TB Update - WOW!
25 inches of water?
---------------------------------------------------
Steve St.Laurent
2000 Dakota 4.7L, CC, Soon to be Supercharged
1999 Chebby gone in 2003
1993 Suzuki Tracker (Geo) 1.6L
COMING SOON
2003 Aspiring for a V-10 GTS-R
2003 Dodge Dakota 5.7 Hemi R/T
-----Original Message-----
From: owner-dakota-truck@buffnet.net
[mailto:owner-dakota-truck@buffnet.net]On Behalf Of Bernd D. Ratsch
Sent: Wednesday, November 15, 2000 4:39 PM
To: dakota-truck@buffnet.net
Subject: DML: RE: Re: Holley TB Update - WOW!
Flowbench measurement: 25" H2O
- Bernd
-----Original Message-----
From: owner-dakota-truck@buffnet.net
Subject: DML: RE: RE: Re: Holley TB Update - WOW!
For us non-automotive engineers, speak English. What does it mean from 28"
or 25"?
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