PRH wrote: ↑Sat Jul 20, 2019 4:00 pm
I thought that the typical way CD was interpreted was against the curtain area.
I’ve also heard about using the actual valve seat specs to calculate the available area between the valve and the seat at the various lifts, and use that instead of the curtain area as the basis for the theoretical flow potential.......which makes sense to me.
(A valve with a 55* seat lifted .100 creates a smaller path than the same diameter valve with a 30* seat lifted that same .100, and the curtain area method doesn’t take that into account).
So, while I totally understand there will be situations where the curtain area will exceed some point of min csa inside the port....... it still makes sense to me having the curtain area(or better yet, the valve job area) be the reference point for the CD....... since, if you open the valve that far........ the potential to use that area exists.
After all, if the same amount of air is moving past the same valve in the same port at .500 lift and .700 lift...... isn’t the air going a little slower as it passes by the valve through the .700 lift opening?
Everyone has their own way that they would like to see the data. When the program was being done David and I decided on a couple of ways that we would show the data.
Stan
shawn-eff-sae-cd.gif
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Everyone has their own way that they would like to see the data. When the program was being done David and I decided on a couple of ways that we would show the data.
Sure, I get that.
Hopefully the software explains how the various curves are derived....... particularly if the method is different from what much of the industry uses........ since it’s inevitable that the charts and graphs generated by the software will be compared to all kinds of other charts and graphs.
Right or wrong...... it’s going to happen.
If the methods as to how the charts and graphs are created is in the software....... it might help ward off some confusion.
Carnut1 wrote: ↑Sat Jul 20, 2019 4:38 pm
Rev, any word on which heads, engines DV is testing?
I don't, Charlie. I've been dealing with a migraine that's been going on for several months now and, when that happens, I tend to turn into the friend that doesn't call to see how things are going.
Hopefully his REC Ford is on schedule and Josephine hasn't cracked him over the head with a skillet and pushed him down the stairs for trying to do too much.
Rev,
Thanks for the confirmation, I plot velocity the same, don't know if mean velocity says alot with low port 23degree head because of velocity gradients throughout the Port, exhaust yes because port so small in area.i think another thing difficult to do is putting pitot tube back in exactly same position when rechecking port position airspeed.
Re your post:- I am assuming DV is short for David Vizard. So is it common on this board to speak of oneself in first person? Or is this possibly someone else posting for him or a glitch. Struck me as funny. Its all good. Anyway. Elroy understands what Elroy read regardless. :lol:
Phil was in my shop at the time and posted on my address - I did the pics for him and that was possibly the reason for the confusion.
DV
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
Everyone has their own way that they would like to see the data. When the program was being done David and I decided on a couple of ways that we would show the data.
Sure, I get that.
Hopefully the software explains how the various curves are derived....... particularly if the method is different from what much of the industry uses........ since it’s inevitable that the charts and graphs generated by the software will be compared to all kinds of other charts and graphs.
Right or wrong...... it’s going to happen.
If the methods as to how the charts and graphs are created is in the software....... it might help ward off some confusion.
PHR,
I don't think it has changed since I was a kid (a long long time ago) but SAE decided to use the valve diameter as the final flow area constraint. That was because calculating the actual area through the throat and on past the seat/valve gap was a long winded process prior to calculators and computers. At the end of the day the available through flow area can never be bigger than the valve. How that valve area is used is up to the user. If the valve area is the limiting factor then, once the lift is over 0.25 of the valve diameter no more through flow area is available regardless of the lift. So after 0.25 D the program uses the valve area regardless of the geometric curtain area generated by the lift.
Hope that answers your questions.
DV
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
steve cowan wrote: ↑Sat Jul 20, 2019 7:24 pm
Rev,
Thanks for the confirmation, I plot velocity the same, don't know if mean velocity says alot with low port 23degree head because of velocity gradients throughout the Port, exhaust yes because port so small in area.i think another thing difficult to do is putting pitot tube back in exactly same position when rechecking port position airspeed.
Steve,
Actually the mean port speed is a telling factor. It allows for an assessment of how well the available port area is being utilized. Probing the port tells what parts are over utilized and what are under utilized.
DBV
David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
Rev Theory unless you know definitively that you have a Migraine going on then please get yourself checked out as you could also have the start of a Brain Tumor and you don't want to give that time to grow!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
Everyone has their own way that they would like to see the data. When the program was being done David and I decided on a couple of ways that we would show the data.
Sure, I get that.
Hopefully the software explains how the various curves are derived....... particularly if the method is different from what much of the industry uses........ since it’s inevitable that the charts and graphs generated by the software will be compared to all kinds of other charts and graphs.
Right or wrong...... it’s going to happen.
If the methods as to how the charts and graphs are created is in the software....... it might help ward off some confusion.
PHR,
I don't think it has changed since I was a kid (a long long time ago) but SAE decided to use the valve diameter as the final flow area constraint. That was because calculating the actual area through the throat and on past the seat/valve gap was a long winded process prior to calculators and computers. At the end of the day the available through flow area can never be bigger than the valve. How that valve area is used is up to the user. If the valve area is the limiting factor then, once the lift is over 0.25 of the valve diameter no more through flow area is available regardless of the lift. So after 0.25 D the program uses the valve area regardless of the geometric curtain area generated by the lift.
Hope that answers your questions.
DV
So, the curtain area up to the point of .25 l/d, then the area of the valve OD above that point.
Thanks for clearing it up.
Last edited by PRH on Mon Jul 22, 2019 12:23 pm, edited 1 time in total.
mag2555 wrote: ↑Mon Jul 22, 2019 12:12 pm
Rev Theory unless you know definitively that you have a Migraine going on then please get yourself checked out as you could also have the start of a Brain Tumor and you don't want to give that time to grow!
I haven't had an MRI since 2004 (they didn't find anything at all, lol) but it's definitely something to keep in the back of my mind, so to speak. I appreciate the comment.
Everyone seem to have their own way they want to see the data. In my software while I don't graph all of the different ways I do try to show the data in my text report.
Stan Weiss wrote: ↑Mon Jul 22, 2019 6:14 pm
Everyone seem to have their own way they want to see the data. In my software while I don't graph all of the different ways I do try to show the data in my text report.
what if you have an upstream secondary choke point that isnt the actual throat? the lift where the "choke" area starts to dictate will be somewhat lower