PTS Flowbench Forum

Finally have my Flow bench up and running,and have done some preliminary testing as a bit of orientation to see how far I can test with 3 1200 Watt/230 volt motors.
In the middle of all the noise I realized the results are way to high for the head being tested.

A little info on my measuring system.
Pressure drop is measured on a "U" Tube manometer, 18" up ,18" down for a total of 36". Testing done at 28"

Pressure differential is measured on an inclined manometer, 23.6" in length ,and 12" inclination for roughly a 30 degree angle.

I have an array of sharp edged orifices machined up,and used the spreadsheet from this forum to determine flow @ 23.6" differential for each.

Orifices used:
1.7" = 189.6 cfm @ 23.6" differential
2.1" = 293.5 cfm @23.6 differential

My cylinder head is a Chevy 462624 casting with 1.94/1.50 valves.This head has never been touched and, in fact, is new from a GM crate engine.
Intake Flow data for these heads @28" pressure drop are as follows.
.100....44 cfm
.200....101 cfm
.300....155 cfm
.400....182 cfm
.500....196 cfm

I tested first with the 1.7"/189.6 cfm orifice and maxed it out @.200 lift
(.200....189 cfm)

I changed to the 2,1"/293.5 cfm orifice and came up with this.
.200....187,8 cfm
.300....242,13 cfm
These heads will never be capable of such low lift flow numbers.Not now and no matter what's done to them.
Something is telling lies to the tune of double what should be.

I did this so far,to find the problem.
I stalled my bench to 28" pressure drop and the differential manometer never moved,so I ruled out air leaks.
I tried several larger orifices and came up with consistant fiqures @.200 lift,around 185 to 190 cfm.

Any Ideas what I'm doing wrong.

What size orifice are you using inside the bench for your Delta P?

Rick

Orifices used:
1st try:1.7" = 189.6 cfm @ 23.6" differential (Delta P)

2nd try:2.1" = 293.5 cfm @23.6 differential (Delta P). It's in there now.

Have you calibrated your bench with a standard orifice say a 100cfm at 28" or a 200cfm at 28" on top of the bench using a head is not the best way to check your bench.

Rick

Found the problem.
Over the holidays,I sent 5 orifices off to have them flow tested,and finally got them back yesterday with the results.
These are extremely sharp edged orifices that I machined myself using an adapter for my lathe.
I used 3 millimeter steel plates ,turned out to various diameters,followed up with a 45 degree angle to produce the sharp edge.Perfectly round ,checked with a dial bore gauge.No burrs and razor sharp.
The flow results @ 24" delta are as follows.

Orifice Flowed Calculated
0,838" = 40 CFM................45,1 CFM
1,20" = 76,5 CFM..............92,5 CFM
1,49" = 116,5 CFM.............142,7 CFM
1,7" = 152,5 CFM..............185,7 CFM
2,1" = 230 CFM..................283,4 CFM

Comparing the test results to the calculations revealed that the lowest range orifice is being calculated 5 CFM higher from the spread sheet than it actually flows.The error gets progressively higher as the orifice range goes up,with the highest range over 50 CFM off track.

I went back to the spread sheet and lowered the discharge coefficient numbers so that the calculated CFM numbers matched the orifice test results.
I have read in different technical articles that 0,61 to 0,65 is the number to use for sharp edged orifices.But,it appears that my orifices, which I payed much time and attention to ,do not have a coefficient of 0,61.More to the tune of 0,487 to 0,53.
Will have to play around some more,trying different back angles maybe.

Anyway,afterwards I flow tested these asthmatic 624 heads again .Using the CFM numbers from the orifice test results as my 100% @ 24" delta ,and the numbers matched up almost exactly to their known flow capabilities.

Even if using these heads to calibrate my bench against their known flow figures was not the right way to do things,I would have never seen the error had I not.

It's been said here, and in many other forums, that to know for sure what an orifice will flow at any giving pressure differential,it's needs to be verified / flow tested.And it holds true.

Ravoll wrote:

Pressure differential is measured on an inclined manometer, 23.6" in length ,and 12" inclination for roughly a 30 degree angle.

I have an array of sharp edged orifices machined up,and used the spreadsheet from this forum to determine flow @ 23.6" differential for each.

Orifices used:
1.7" = 189.6 cfm @ 23.6" differential
2.1" = 293.5 cfm @23.6 differential

My cylinder head is a Chevy 462624 casting with 1.94/1.50 valves.This head has never been touched and, in fact, is new from a GM crate engine.
Intake Flow data for these heads @28" pressure drop are as follows.
.100....44 cfm
.200....101 cfm
.300....155 cfm
.400....182 cfm
.500....196 cfm

I tested first with the 1.7"/189.6 cfm orifice and maxed it out @.200 lift
(.200....189 cfm)

I changed to the 2,1"/293.5 cfm orifice and came up with this.
.200....187,8 cfm
.300....242,13 cfm
These heads will never be capable of such low lift flow numbers.Not now and no matter what's done to them.
Something is telling lies to the tune of double what should be.

I did this so far,to find the problem.
I stalled my bench to 28" pressure drop and the differential manometer never moved,so I ruled out air leaks.
I tried several larger orifices and came up with consistant fiqures @.200 lift,around 185 to 190 cfm.

Any Ideas what I'm doing wrong.

The way I read this you have a 12" rise and a scale that is 23.6" long? If that is the case you have a 12" Delta P not a 23.6"

This is what I was told by the author of the spread sheet.

http://www.flowbenchtech.com/forum/view ... f=3&t=1248
Also a pic of my inclined scale setup included.

According to the copied spreadsheet below,my Dp(WC/Inches) @100% is 23.9"
This is what I was told to enter for the "pressure difference WC inches" in the "orifice flow and size" page.

So now what?

Tube I.D. 0,393 0,154449
Reservoir I.D. 3,18 8,0772
Scale Length 23,600 599,44
Scale Vetical Height 12,0 304,8
Fluid density 1,940 Don't change values in Blue. They are calculated values
Scale Angle 30,56227535

Incline Manometer Scale
% of flow Ds (in) Dp (WC in) mm
1,0% 0,0024 0,00 0,059944
2,0% 0,0094 0,01 0,239776
3,0% 0,0212 0,02 0,539496
4,0% 0,0378 0,04 0,959104
5,0% 0,0590 0,06 1,4986
6,0% 0,0850 0,09 2,157984
7,0% 0,1156 0,12 2,937256
8,0% 0,1510 0,15 3,836416
9,0% 0,1912 0,19 4,855464
10,0% 0,2360 0,24 5,9944
11,0% 0,2856 0,29 7,253224
12,0% 0,3398 0,35 8,631936
13,0% 0,3988 0,41 10,130536
14,0% 0,4626 0,47 11,749024
15,0% 0,5310 0,54 13,4874
16,0% 0,6042 0,61 15,345664
17,0% 0,6820 0,69 17,323816
18,0% 0,7646 0,78 19,421856
19,0% 0,8520 0,87 21,639784
20,0% 0,9440 0,96 23,9776
21,0% 1,0408 1,06 26,435304
22,0% 1,1422 1,16 29,012896
23,0% 1,2484 1,27 31,710376
24,0% 1,3594 1,38 34,527744
25,0% 1,4750 1,50 37,465
26,0% 1,5954 1,62 40,522144
27,0% 1,7204 1,75 43,699176
28,0% 1,8502 1,88 46,996096
29,0% 1,9848 2,02 50,412904
30,0% 2,1240 2,16 53,9496
31,0% 2,2680 2,30 57,606184
32,0% 2,4166 2,46 61,382656
33,0% 2,5700 2,61 65,279016
34,0% 2,7282 2,77 69,295264
35,0% 2,8910 2,94 73,4314
36,0% 3,0586 3,11 77,687424
37,0% 3,2308 3,28 82,063336
38,0% 3,4078 3,46 86,559136
39,0% 3,5896 3,65 91,174824
40,0% 3,7760 3,84 95,9104
41,0% 3,9672 4,03 100,765864
42,0% 4,1630 4,23 105,741216
43,0% 4,3636 4,43 110,836456
44,0% 4,5690 4,64 116,051584
45,0% 4,7790 4,86 121,3866
46,0% 4,9938 5,07 126,841504
47,0% 5,2132 5,30 132,416296
48,0% 5,4374 5,52 138,110976
49,0% 5,6664 5,76 143,925544
50,0% 5,9000 5,99 149,86
51,0% 6,1384 6,24 155,914344
52,0% 6,3814 6,48 162,088576
53,0% 6,6292 6,74 168,382696
54,0% 6,8818 6,99 174,796704
55,0% 7,1390 7,25 181,3306
56,0% 7,4010 7,52 187,984384
57,0% 7,6676 7,79 194,758056
58,0% 7,9390 8,07 201,651616
59,0% 8,2152 8,35 208,665064
60,0% 8,4960 8,63 215,7984
60,5% 8,6382 8,78 219,410026
61,0% 8,7816 8,92 223,051624
61,5% 8,9261 9,07 226,723194
62,0% 9,0718 9,22 230,424736
62,5% 9,2188 9,37 234,15625
63,0% 9,3668 9,52 237,917736
63,5% 9,5161 9,67 241,709194
64,0% 9,6666 9,82 245,530624
64,5% 9,8182 9,98 249,382026
65,0% 9,9710 10,13 253,2634
65,5% 10,1250 10,29 257,174746
66,0% 10,2802 10,45 261,116064
66,5% 10,4365 10,60 265,087354
67,0% 10,5940 10,76 269,088616
67,5% 10,7528 10,93 273,11985
68,0% 10,9126 11,09 277,181056
68,5% 11,0737 11,25 281,272234
69,0% 11,2360 11,42 285,393384
69,5% 11,3994 11,58 289,544506
70,0% 11,5640 11,75 293,7256
70,5% 11,7298 11,92 297,936666
71,0% 11,8968 12,09 302,177704
71,5% 12,0649 12,26 306,448714
72,0% 12,2342 12,43 310,749696
72,5% 12,4048 12,60 315,08065
73,0% 12,5764 12,78 319,441576
73,5% 12,7493 12,95 323,832474
74,0% 12,9234 13,13 328,253344
74,5% 13,0986 13,31 332,704186
75,0% 13,2750 13,49 337,185
75,5% 13,4526 13,67 341,695786
76,0% 13,6314 13,85 346,236544
76,5% 13,8113 14,03 350,807274
77,0% 13,9924 14,22 355,407976
77,5% 14,1748 14,40 360,03865
78,0% 14,3582 14,59 364,699296
78,5% 14,5429 14,78 369,389914
79,0% 14,7288 14,97 374,110504
79,5% 14,9158 15,16 378,861066
80,0% 15,1040 15,35 383,6416
80,5% 15,2934 15,54 388,452106
81,0% 15,4840 15,73 393,292584
81,5% 15,6757 15,93 398,163034
82,0% 15,8686 16,12 403,063456
82,5% 16,0628 16,32 407,99385
83,0% 16,2580 16,52 412,954216
83,5% 16,4545 16,72 417,944554
84,0% 16,6522 16,92 422,964864
84,5% 16,8510 17,12 428,015146
85,0% 17,0510 17,33 433,0954
85,5% 17,2522 17,53 438,205626
86,0% 17,4546 17,74 443,345824
86,5% 17,6581 17,94 448,515994
87,0% 17,8628 18,15 453,716136
87,5% 18,0688 18,36 458,94625
88,0% 18,2758 18,57 464,206336
88,5% 18,4841 18,78 469,496394
89,0% 18,6936 18,99 474,816424
89,5% 18,9042 19,21 480,166426
90,0% 19,1160 19,42 485,5464
90,5% 19,3290 19,64 490,956346
91,0% 19,5432 19,86 496,396264
91,5% 19,7585 20,08 501,866154
92,0% 19,9750 20,30 507,366016
92,5% 20,1928 20,52 512,89585
93,0% 20,4116 20,74 518,455656
93,5% 20,6317 20,96 524,045434
94,0% 20,8530 21,19 529,665184
94,5% 21,0754 21,41 535,314906
95,0% 21,2990 21,64 540,9946
95,5% 21,5238 21,87 546,704266
96,0% 21,7498 22,10 552,443904
96,5% 21,9769 22,33 558,213514
97,0% 22,2052 22,56 564,013096
97,5% 22,4348 22,80 569,84265
98,0% 22,6654 23,03 575,702176
98,5% 22,8973 23,27 581,591674
99,0% 23,1304 23,50 587,511144
99,5% 23,3646 23,74 593,460586
100,0% 23,6000 23,98 599,44

What type of fluid are you using in your manometer? You need to put in the correct specific gravity for the fluid you're using, for water it would be 1.0. I'm not entirely sure how I ended up putting 1.940 there but I think that's the specific gravity of Dwyer blue manometer oil.

It's water with blue food coloring..Does that count?

I was wondering the same at one time or the other what the 1,9 fluid density was representing.
g/cm3, kg/m3, sp. gr. lb/ft3, or lb/gal? If your saying 1, then seems to be g/cm3.
I had messed around a bit with the calculations ,changing the density,but just wasn't sure.What throws me off is ,in the Inclined scale compensation it seems to be represented as grams,but in Orifice flow and size it's represented as lb/ft³.

When I change it in the scale compensation to 1,then I do come up with 12,36" as my delta P WC.It also puts my Discharge coefficient back up ( 0,68) closer to my orifice test results.Now I'm getting somewhere.

My scale length @100% will still be 23,6"?

Ravoll wrote: Scale Vetical Height 12,0 304,8

This is your Delta P

The scale length can be any number it is just what the rise is measured on to get your reading off of, you are projecting the rise of water (12") along the length of your scale to measure the small changes easier.

So all your internal orifice plate calculations are based on a 12" Dp which you are reading on your 23.9" length