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owbench-guided cylinder head designs in the early 1970s as well. Chrysler adapted a ow lab from
elements that were used in air lter work, and the lab was developed in parallel with their introduction of the
426 Hemi engine. The Ford Motor Company ow lab dates to the mid-1960s where they supported their
winning LeMans racing eort with their GT40 racing vehicles.
Some of the OEM, specialty-engine manufacturers, and professional race teams are now using
Computational Fluid Dynamics (CFD) to assist in Computer-Aided Design (CAD) and owbench driven
designs. Many of the OEMs have abandoned their in-house airow benches to outsource much of
their airow development testing. As a result, some well-established shops using SuperFlow or other
owbenches around the country typically get involved in OEM development contracts because the
programs are more cost and time eective.
7.2 Test Pressures and Comparing Flow Numbers
The necessity of ow number comparison is something anyone involved in ow testing must endure. Even
if the number comparison is made on the same components and owbench, it is important to know how
to compare the numbers so the time and eort is worthwhile. The comparison process is necessary to
evaluate published numbers vs. your own developed ow numbers. The rst principle you learn in ow
testing is that you must ask (or qualify) at what test pressure the ow numbers were recorded.
"Table 7-1. Flowbench Test Pressure Conversion Chart" is based on the square root of the pressure ratio
method. If you have ow numbers at a known test pressure and want to compare those numbers at a
dierent test pressure, it is easy to do. The formula is:
= FlowAtSecondTestPressureX
SecondTestPressure
FirstTestPressure
As an example, if you have ow numbers at 10"H
2
O test pressure and would like to know what the ow
should be at 25"H
2
O test pressure, the formula is:
So you would multiply the ow numbers taken at 10”H
2
O test pressure by 1.58 to see what the ow would
be at 25"H
2
O.
7.0 Flowbench Theory
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