PTS Flowbench Forum

I want plot discharge coefficient against the lift?
seems the discharge coefficient equal effective flow area over curtain area,

so How to calculate the effective flow area?
or how to calculate the discharge coefficient of the port??
thanks

I put this together a few years ago to do just this function that you are asking. It is a microsoft xcel file but if you have openoffice you can also open it with that. It has quite a few functions. I have tried to make it as straight forward as possible. Look at the bottom for the tabs for the different functions.

John

PLEASE NOTE! I just checked this and it only works correctly in Microsoft Excel. It does not calculate the CD when trying to use it in OpenOffice

jfholm wrote:I put this together a few years ago to do just this function that you are asking. It is a microsoft xcel file but if you have openoffice you can also open it with that. It has quite a few functions. I have tried to make it as straight forward as possible. Look at the bottom for the tabs for the different functions.

John

PLEASE NOTE! I just checked this and it only works correctly in Microsoft Excel. It does not calculate the CD when trying to use it in OpenOffice

THANKS VERY MUCH.
you answer is straight to my question, I checked the xcel file, it works well on my computer.
according to your equation IF(G7<=G3,SUM(C7/(G7*F5),IF(G7>G3,SUM(((C7/(G3*F5)))),FALSE)),FALSE) etc
the discharge coefficient is equal CFM/(Valve flow curtain area*CFM flow for 1 sq. in. of ideal standard orifice)
why？ could you explain it more deeply？？

What you are measuring is how well your port with valve in place flows compared to a standard orifice. You will notice that the reading of 145.7 cfm is for a standard orifice of 1 square inch at 28" h2o. The program calculates the square inches of the curtain area. So if your valve was opened to where the curtain area was 1.0 square inches and flowed 145.7 cfm you would have a CD of 1.00. Now if the port only flowed .700 CD that means your port is only flowing 70% of what a standard orifice flows or roughly 102 cfm.

On my cylinder head at .500" valve lift I have 3.22 square inches of area and flows 254 cfm. Now if it was a standard orifice it would flow 3.22 times 145.7 or 469.15 cfm. My port only flows 254 so it has a CD of .541 or 54.1% of the standard area orifice of an area of 3.22 square inches. The higher the CD of your port then the better performing it will be. Usually a 2" intake that flows the same as a 2.05" intake valve at the same lift will perform better because it has a better CD. If my intake valve was only 2.00" instead of 2.05" than my CD at .500" lift would be .555 instead of .541.

John

jfholm wrote:What you are measuring is how well your port with valve in place flows compared to a standard orifice. You will notice that the reading of 145.7 cfm is for a standard orifice of 1 square inch at 28" h2o. The program calculates the square inches of the curtain area. So if your valve was opened to where the curtain area was 1.0 square inches and flowed 145.7 cfm you would have a CD of 1.00. Now if the port only flowed .700 CD that means your port is only flowing 70% of what a standard orifice flows or roughly 102 cfm.

On my cylinder head at .500" valve lift I have 3.22 square inches of area and flows 254 cfm. Now if it was a standard orifice it would flow 3.22 times 145.7 or 469.15 cfm. My port only flows 254 so it has a CD of .541 or 54.1% of the standard area orifice of an area of 3.22 square inches. The higher the CD of your port then the better performing it will be. Usually a 2" intake that flows the same as a 2.05" intake valve at the same lift will perform better because it has a better CD. If my intake valve was only 2.00" instead of 2.05" than my CD at .500" lift would be .555 instead of .541.

John

Thanks for knowledge you delivered, John.

Happy new year 2014!

Meaning of CFM/sqr inch?
Would there be any idea if limiting (smallest) area at that lift is used? When MCSA will become limiting area that is used instead curtain area?

Juhani