TRYING TO BUILD A FLOW BENCH HELP!!!

[Tony]

What you have done sounds fine.

If you are planning to use that 1.78" orifice as your measurement orifice, then you need to adjust the slope of your sloping manometer so the 100% flow mark is 16.4" higher than the 0% flow mark.

You then know that 100% flow = 173.8 CFM.

You can verify this by fitting the other 1.78" orifice over your test hole.
When your test pressure is adjusted to 16.4", your sloping manometer should just read 100%.
If it does not, adjust the manometer slope very slightly to get it reading exactly 100%

It should now be possible to very accurately measure flow between 86.9 CFM (50%) and 173.8 CFM (100%)

[swnf]

Thanks, for your help.
Let you know how it turns out.

[swnf]

Got to tinker some this evening, had a idea today, put the 2.020 plate inside, put the 1.78 plate on top run the bench up to 240mm wc. (should have set it to 236mm because that is the wc height the 2.02 plate is figured 168cfm so the numbers are a little off) 78% of 168 is 131 and 131 is what the 1.78 plate should flow. The incline went up to 79.5% I was shocked. So do I adjust the incline to read 78% and call it good or what? Am I getting it now? I have the right side of my u-tube hooked up for test pressure when it pulls up to 236mm the incline height should be 472 and that is where 100% should be
Is my bench working right now ?

[Tony]

That sounds about right.

You wound up your test pressure to 236mm across your 1.78" test piece.
That is 9.29 inches of test pressure, or about 168 CFM by my reckoning.

The 2.02 inch measurement orifice should require a flow of 223 CFM to reach the 100 percent flow mark that was previously adjusted to 16.4 inches height above zero.

The flow manometer reads 79.5% of 223 CFM which works out to 177 CFM.

So the test piece says 168 CFM
And the flow manometer says 177 CFM

A 5.3 % difference.

Allowing for a bit of error here and there, not a bad first attempt.

Well done, certainly nothing to be shocked by.

[swnf]

How should I go about getting that 5.3% out

[Tony]

How should I go about getting that 5.3% out

The error could come from quite a few places, including my own wobbly rounded maths.

First thing to try is placing a 1.78 inch orifice in each location and make sure that the water rise in both manometers is exactly the same 16.4 inches. If it is not, swap the orifices over and try again.

That should give you an idea if both orifices are flowing exactly the same.

If you find the flow orifice reads consistently different to the measurement orifice, there are several possibilities. The measurement orifice might be being hit with turbulent air, or there could be something wrong your pressure measurement locations, or even an air leak somewhere.
Or maybe you just need to tweak the manometer slope very slightly.

All this is pretty normal for firing up a brand new bench, so don't worry.
A bit of messing around is actually good at the start, you will gain a much better understanding of the whole process.

Anyhow try a few different things and see what happens.

[200cfm]

Have you tried this. Put both the test manometer and the incline manometer in parallel to each other and use a vacumn / brake pressure bleeder pump to calibrate the incline to the test manomoter. You will have to use some "T" connection and disrupt your bench connections for the test. When the incline is at the proper angle the water levels on both manometers will track together. My internal plates have a 12" wc reference so when the test manomoter reaches 12" wc then the incline should reach 100%. If the angle is correct the vertical equivalent rise on the incline is also 12" wc. I have my incline marked for the equivalent test pressure readings. 5", 8" 10" 11" and 12". When the incline is properly zeroed and angled for the equivalent 5,8,10,11,12 rise, each of the 5 points will hit within 1 mm. Hope this helps.

[swnf]

Think I am getting close now . Can someone point me in the right direction to change 236mm wc to 28" wc I flowed my heads and cfm numbers seem low but i only been testing at 236mm wc . Thanks again for your help

[Tony]

236mm is 9.291 inches test pressure.

If you went up to 28 inches test pressure, that would be x 3.013 times the test pressure.

Square root of 3.013 is 1.736

Multiply whatever flow you get at 236mm by 1.736 to get the flow at 28 inches.

[swnf]

I have not tried to get the 5% out yet but have tested my heads on one exhaust port, pulling through the port do not know how much of a difference it would make blowing through the port but anyway here is the numbers I came up with.

Did all test at 236mm wc 1.779 orifice at 100% should be 131cfm. Started at .300 up to .800


.300 63% of 131=83...........*1.736 to get flow at 28"= 144
.400 72% =94 163
.500 76% =99 172
.600 79% =103 179
.700 81% =105 182
.800 82% =107 186

same 236mm wc but with a 2.02 orifice at 100% should be 169cfm. Started at .300 up to .800

.300 53% of 169=90.............*1.736 to get flow at 28" =156
.400 60% =101 =174
.500 63% =106 =184
.600 65% =110 =190
.700 67% =113 =196
.800 67% =113 =196

difference between plates at 236mm wc
2.02 1.779
90 - 83=7
101 - 94=7
106 - 99=7
110 - 103=7
113- 105=8
113 - 107 =6
is this my 5%
should i use the 1.779 orifice or the 2.02
point out all my errors please
going to work on the bench some this weekend
cfm numbers are close , I think for a big block ford head ,form what was found on a ford website