Got the new negative/positive gage on the inlet side
and here are the results.

4200 RPM air slug .95 dia by 3.6 " long

Flow   press   press    press 
GPM  outlet  flow meter inlet
Closed  8      8        -13
15      7      7        -10
20      6      6        -9
25      6      6        -8
30      6      6        -8
35      6      6        -7
40      5.5    5        -5
45      5      4.5      -4
55      6      4        -3
65      5      4        -2
75      5      3.5       0

off     2.5    2.5      2.5                


2800 RPM air slug .95 dia by 3.6 " long

Flow   press   press    press 
GPM  outlet  flow meter inlet
Closed  4      4        -3
15      4      4        0
20      4      4        0
25      4      4        0
30      4      4        0
35      3.5    3.5      1
40      3.5    3.5      2
45      3.5    3        2.5
55      3      2.5      2

off     2.5    2.5      2.5                

Found a bit more RPM with a slightly different mill step pulley 
arrangement.

4300 RPM air slug .95 dia by 5" long

Flow   press   press    press 
GPM  outlet  flow meter inlet
Closed  7      7        -15
15      5      5        -14
20      5      5        -13
25      4.5    4.5      -12
30      4      4        -11
35      4.5    4.5      -11
40      4      3.5      -10
45      4      3.5      -8

off     0      0        0

The lack of pre pressure (2.5 V 0) had more to do with the
differences than the amount of trapped air.

In the next couple of days I will test the stock Mazda
pump housing with the same impeller. I have a 1.5 inch dia 90 degree bend on 
order from Burns Stainless to adapt the stock pump to this test rig.

Also found a five HP horizontal mill I can use next week.

Paul Lamar
 
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