orifices and cfm at 28in h20 Question

sheppard00 · Post by **sheppard00** » Sun Jun 19, 2005 6:52 pm

are the sizes and cfm rating's on this website good

http://www.diyporting.com/flowbench.html

I need to know the cfm for these size orifices

3/4

1/2

1/8

7/8

brucepts · Post by **brucepts** » Sun Jun 19, 2005 7:34 pm

Some pretty indepth discussions on this subject on my flowbench forum located here:

http://www.tractorsport.com/cgi-bin/for ... nboard.cgi

Look in the orifice flowbench area . . . you will be enlightened on orifice design. I personally use a pitot style bench using the Flow Performance Processor with the laptop upgrade that is displayed on the website you posted.

sheppard00 · Post by **sheppard00** » Sun Jun 19, 2005 11:23 pm

thanks I wish I had excell so that I could look at one of the charts posted...lol

PFM · Post by **PFM** » Sun Jun 19, 2005 11:30 pm

Mark,

What are you trying to do? An 1/8" orifice is darn small for anything relating to engines. There are formulas out there for area of a sharp edge orifice plate area to airflow but there are issues when the hole gets this small. I'm with Brucepts and also have Flow Performance Processor in my bench 600 CFM at 38" WC. If you are working on a flow bench they can save you a bunch of time, my project was in limbo for years waiting for something like this. Check it out http://www.flowperformance.com/

PFM

bill jones · Post by **bill jones** » Sun Jun 19, 2005 11:46 pm

-I have flowtested 1/8" thick sharp edge orifices that I made myself on my Superflow 300 flowbench and I found you can expect 84.4CFM per square inch of area at 25" test pressure.
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-1.0583 times 84.4 is what you should see at 28" so that would be 89.3CFM per square inch of area.
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-3/4" = .4418SIA so that hole would flow 39.45CFM at 28"
-5/8" = .306796SIA so that is 27.397CFM at 28"
-7/8" = .60132SIA equals 53.698CFM at 28"
-1/8" = .012272SI egauls 1.098CFM at 28"

PFM · Post by **PFM** » Mon Jun 20, 2005 12:03 am

Bill,

Nice work that is within 1 percent of the numbers that I have but.... I do not think the 1/8" hole will have the same flow / area numbers. The vena contracta (spelling) will reduce the number quite a bit. The 5/8 number will even be reduced a bit, the larger holes should be so close as to not be able to measure the error.

PFM

sheppard00 · Post by **sheppard00** » Mon Jun 20, 2005 7:07 am

I'm building a bench and didn't know about this site untill after I have already made the disk... I was trying to avoid having my disk flowed because the only person with a sf600 within 100 miles is realy high $ it will probably cost me $200 just to get the disk flowed.... but I want' it to be close untill I can buy a processor... I used multiple holes in my disk and those are the hole sizes I used I was wanting 1- setting for flowing 100cfm @ 28in h20 and 200, and 300, and 400. those are accualy hole saw bits and drill bit sizes that I have already...

Ape · Post by **Ape** » Mon Jun 20, 2005 9:27 am

Hi,
im also occasionally on the flowbenchforum, there should be quite valuable info on orifice type benches as i do use a orifice style one (hi bruce, by the way). As mentioned comp interfaces make the job easier or just using a plain exxel sheet, as i do to feed the manual data into(time consuming though). there should be great info on how to calculate the coeeficients leading to the cfm´s on the froum, but i would stay away from multiple holes, and also i would recommend a nice machinist or the forum for getting nicely made (lathe) orifices, since i wouldnt trust circle saws. but in order to not get offtopic, just use the search function extensively on the flowbenchforum and you´ll find what you need.

christian