figuring flow from depression?

[bc]

Is there a way to figure what a head would flow if you just know the depression that the bench can pull it at. Example. Head A flows x amount at 15" of vacuum (bench is maxed out). Head B flow so more that the bench can only get 6" of vacuum out of the head. Is there a way to no what what B flows based off of knowing the cfm of head A and the depression difference between the heads A and B. By the way I only asking out of mathematical curiosity. Just wondering if it can be figured out. If so how?

[John Wallace]

Not sure if this is exactly what you want.
http://www.wallaceracing.com/calcdchg.php

[bc]

No that is just converting from one depression point to another.

[bill jones]

-when I get to that point on my bench which is about 360CFM at 25" and I need to know what the flow is of those occasional heads that flow more than 360---I drop my flow testing down from 25" to say 15" and then do the math.
-I use a superflow 300 and the intake scale is 424.7 at 100% and at about 84.4% on that scale my machine is all maxed out.
-So I will drop down to 15" and finish my testing and do the square root math on the numbers.
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-example is if you the head flowed 75% on the 426.7 scale at 15" how much does it flow at 28"?
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step 1:

28 divided by 15 = 1.8666667

1.8666667 and hit the square root key equals 1.36626.
-------------------------
step 2:

426.7 times .75 (75%) equals 320cfm at 15" test pressure

320cfm times 1.36626 equals 437.2cfm (converted up from 15" to 28")

[crazycuda]

Is there a way to figure what a head would flow if you just know the depression that the bench can pull it at. Example. Head A flows x amount at 15" of vacuum (bench is maxed out). Head B flow so more that the bench can only get 6" of vacuum out of the head. Is there a way to no what what B flows based off of knowing the cfm of head A and the depression difference between the heads A and B. By the way I only asking out of mathematical curiosity. Just wondering if it can be figured out. If so how?

There is no real way to calculate the flow numbers just by the depresion unless you know the orifice flow rate. In other words if you have an orifice that flows 200 cfm at 15". Then you mount Head A on the bench and it flows 100% @15" then head A would flow 200 cfm at 15". now If you take head B and put it on the bench with the same orifice and you only pull 6" at 100%flow. That tells you that the head flows 200 cfm @ 6". you will then have to convert 200 cfm at 6" to 15" to get an "estimated" flow number to compair the heads.
This is a very rudamentary explination

[panic]

The square root conversion method is only approximate - the formula is accurate but the same head will not flow those exact numbers.

[bc]

Thanks for the help guys. So if I have a head that I know flows 250cfm at 28" and put it on a bench that maxed out can only pull 15" then that head should flow 183cfm at the 15", correct? So if I take head B and put it on the same bench and it is only able to pull 6" is it safe to say that, that head flows 183cfm at 6" so it would flow 395 at 28". Any of these making sense?

[bill jones]

-like Panic says-the square root numbers are for getting some sort of a comparison and the heads SHOULD flow close to those square rooted numbers, but may not be quite exact in real life.
-I just use the square root method and live with it.

[Rick360]

I think I understand the question now.

Thanks for the help guys. So if I have a head that I know flows 250cfm at 28" and put it on a bench that maxed out can only pull 15" then that head should flow 183cfm at the 15", correct?

This part is correct. The same head when tested at different pressures/depressions should be close to the square root conversion.

So if I take head B and put it on the same bench and it is only able to pull 6" is it safe to say that, that head flows 183cfm at 6" so it would flow 395 at 28". Any of these making sense?

This part is wrong. You are confusing the flow curve of the motors/bench with the head. The bench has a different curve that increases flow with reduced test pressure, since it is the source of the flow and pressure. This is opposite what a port does. The flow/pressure curve is also unique to that flowbench and can't be used to calculate flow like that. A bench that flows 183cfm at 15" maxed out would likely flow 250-300cfm at only 6" test pressure. It is completely depenent on the design of the vacuum motors.

Rick