Thank you Mr. Wizard, now I understand, very cool indeed.
Josh
00 CC V6
>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
>
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
Share information about yourself, create your own public profile at
http://profiles.msn.com.
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:57:23 EDT