Motorsports Village

curtain area
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Author:  zums [ Thu Sep 27, 2012 8:44 pm ]
Post subject:  curtain area

i hear sayings like, it didnt flow more on the bench but the curtain area velocity was up, how can you measure curtain area velocity on the in port with a j shaped probe, or is this just calculated, thanks again- tom

Author:  randy355 [ Thu Sep 27, 2012 9:58 pm ]
Post subject:  Re: curtain area

Tom, if a port didn't flow more on the flow bench, the only way the velocity would be up is because the area (window area in this case) is less. If flow didn't change and velocity did, then the area had to change. I'm talking average velocity for a given area. It's possible flow and area could stay the same and velocity increase in one area of the window, but in this case velocity would have to go down in a different area. If flow and area didn't change, the average velocity didn't either, but local areas could.

The most likely way window velocity could change is with a steeper, or shallower valve job. This changes the window area, and generaly the flow curve.

Author:  rick360 [ Thu Sep 27, 2012 10:33 pm ]
Post subject:  Re: curtain area

^^^^ What Randy said
and ...

You can measure curtain area velocity with a L-shaped probe if you mount the head on the bench with the intake flange bolted to an adapter to the bench and have a cylinder a few inches long attached to the head and flow in exhaust mode (blowing out) so the air enters the intake port entrance and flows out into the cylinder facing out where you can see into it. You can stick a probe into the cylinder and measure velocity at the valve curtain. It isn't easy to setup but it can be done for probing in the chamber and cylinder.

You also have to remember there is a lot of BS on the internet and people saying what that guy said because everybody thinks that guy is smart or that other guy knows what he's doing so they parrot back what he says. I've seen it plenty.


Author:  zums [ Fri Sep 28, 2012 9:01 pm ]
Post subject:  Re: curtain area

thanks randy- rick , yea i know what you mean about the internet bs and have a good idea of the parrots, ive tried blowing through the in port, thats a slow learning curve, i also made up a plastic valve head, same shape -back angle , seat ect with a hollow stem and connected the top to an aux water mano with a .04 L shape brass tube even with the valve bottom of the margin, the mano #s almost read reverse of what i get with the pitot for high velocity areas while blowing out of the in port?? when you speak of window area, the term seems like it could be the ss area, throat or real curtain area, which is the real window area, thanks alot guys

Author:  rick360 [ Fri Sep 28, 2012 9:19 pm ]
Post subject:  Re: curtain area

Window area and/or curtain area (same thing) is the area between the valve seat and valve face. It is normally thought of as a cylinder shaped area but is really a cone shape from the inside edge of the valve face to the outside edge of the valve seat when the valve is open much at all.

A probe perpendicular to flow like I think you are describing at the valve edge WILL read lower pressure with higher velocity and the normal pitot probe reads more differential with higher velocity.


Author:  zums [ Fri Sep 28, 2012 9:41 pm ]
Post subject:  Re: curtain area

thanks rick- i saw your method of calculating curtain area on speedtalk a while ago, very slick, thats the true deal, i think the bench is ringing my brains, if the flow is quicker past my pick up point <90*> to the flow, the faster fps would show lower pressure ,simple physics law, seems like you just have to see it in print to remember or have it sink in-thanks again

Author:  zums [ Fri Sep 28, 2012 10:23 pm ]
Post subject:  Re: curtain area

i thought about that and checked my notes, with the tap valve in the head with the line hooked up to the top of the aux mano and bottom vented, shouldnt the highest aux mano reading <vac> match the highest fps reading from the pitot with the head reversed

Author:  rick360 [ Fri Sep 28, 2012 10:36 pm ]
Post subject:  Re: curtain area

Yes, that sounds right if that is how it was hooked up and you were blowing thru the intake port into the chamber. Hmmm maybe the pitot static ports are too far from the tip and picking up some other influence. Pitots were really designed for straight ducts. Hard to say, but I will bet anything the air did the same thing each way. =; Everything you test can send you down the wrong path or turn on a light. It is good to test different methods to validate your info like you did. That keeps the trips down the wrong path as short as possible.


Author:  zums [ Sat Sep 29, 2012 8:53 am ]
Post subject:  Re: curtain area

ok, thanks rick- one last thing, when probing with the chamber facing you what area-casting seat, valve margin/seat do you probe to get the most accurate results, i would guess around.25l/d ss seperation would start to show so would the seat in the head be more accurate, seems like the flow might be able to reorganize a certain amount around the valve head even though the seat could be seperating- by the way, between you and randy i got say the info you share is much appreciated, better than the books i have or i wouldnt be bothering you guys

Author:  rick360 [ Sat Sep 29, 2012 1:20 pm ]
Post subject:  Re: curtain area

zums wrote:
when probing with the chamber facing you what area-casting seat, valve margin/seat do you probe to get the most accurate results

What is accurate? Measuring either place accurately will give you accurate results. If you mean which is more important then I don't think it matters as long as you are measuring it the same all the way around the valve and doing it the same from test to test. IMO the thing to learn from testing with a probe in the chamber is how the air is entering the chamber and particularly how evenly it is coming into the chamber around the valve. You want the air flowing as evenly as possible all around the valve, not a bunch entering on one side and very little on the other. I don't think the actual velocity of any place in particular in the chamber is important.

I think either area you mentioned should give about the same velocities if the probe is at the correct angle unless the static ports are too far out of the stream. Closer to the valve and away from the seat may give a little lower readings.


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