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 Floating Depression? 
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Joined: Sun May 29, 2011 7:52 pm
Posts: 41
Location: central Illinois
some very good thoughts! (and much to mull over)

I have wanted to build in a temp/baro/humidity/altitude correction into what i am doing from the getgo and am going to work on this on the newer build. any good thoughts on this would be of help. on the voltage i believe i would like to just aquire a variac and not have this be of concern. some on ebay for 90bucks 20 ampand will run the air movers i have. and like you say, usable if(if) i jump ship.

on known orifices, would you think the 3 PaP copies (100,200,300)would be enough to test the range here? with current air power the smallest should be near perfect 100% at real 28". the others would likely see a depression(if nothing changes) around 18.25" on the 200 and 11.25" on the 300. I'm having mental block on how the sizing works, i know at say 10" it will take a much larger orifice to flow a real 300 than at 28. will the % flow become too small? just looking at some stuff here are we looking at around :?: a 2"orifice at 300@28". should same plate flow in ballpark of 170 at 10"? will more data points be required?

any help on the stuff that makes my head hurt is greatly appreciated!

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Jason


Sat Jul 16, 2011 3:22 pm
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Jason,

Since what you are doing is not flowing through a plate, all you need to do is download the flow through and orifice spreadsheet, plug in the numbers and you will have the flow at what ever depression you are pulling. Remember since you are using a vertical monometer it will be a little less accurate as the sensitivity is less.

Rick


Mon Jul 18, 2011 4:07 pm
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Joined: Sun May 29, 2011 7:52 pm
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Location: central Illinois
Rick- 10-4, and thanks

I downloaded that spreadsheet awhile back-its neat. is it for sharp edge only or does the thickness of a given orifice change it? mostly cd i'm guessing? and would also need 2 identical for a homemade(i realize paps are well documented, this part just for play!). been noodling around (learning) will probably test out things for awhile to see how things work a little more (been fun!) Time is going to become premium soon for me (school starts 4 weeks) so may be a while before any updates.

Thanks again!

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Jason


Tue Jul 19, 2011 1:47 pm
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Quote:
I downloaded that spreadsheet awhile back-its neat. is it for sharp edge only or does the thickness of a given orifice change it? mostly cd i'm guessing?


Thickness effects CD, example a sharp edge may test out at .6200 and a 1/8" thick sqauare edge at .5800 +/_

Rick


Tue Jul 19, 2011 2:59 pm
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Location: Maryland
Ok,

Here goes I have an in depth post i would like to put up to clear the air on this concept of using a multidimensional restriction and the change in depression against it to validate improvements or negative effects on flow and some of the history there in.

I personally believe the CD of a port is continually changing and unless you have a standard to compare to (internal bench orifice, Pito, LFE) you have no idea if your modifications that may effect restrictions actually increased flow or hurt it. I struggle with this concept but today stumbled across this video where flow was maintained at standard and the depression change was evaluated. Yes i know the hard edge is changing the initial CD of the pipe, but could you not have a similar effect in your grinding?

watch and tell me what you think?

Rick



Sat Jul 23, 2011 8:43 pm
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Location: Grantsville, Utah 45 min west of Salt Lake City
1960FL wrote:
Ok,

Here goes I have an in depth post i would like to put up to clear the air on this concept of using a multidimensional restriction and the change in depression against it to validate improvements or negative effects on flow and some of the history there in.

I personally believe the CD of a port is continually changing and unless you have a standard to compare to (internal bench orifice, Pito, LFE) you have no idea if your modifications that may effect restrictions actually increased flow or hurt it. I struggle with this concept but today stumbled across this video where flow was maintained at standard and the depression change was evaluated. Yes i know the hard edge is changing the initial CD of the pipe, but could you not have a similar effect in your grinding?

watch and tell me what you think?

Rick



Flow was not maintained Rick. When he put the cardboard on, the CFM dropped and when he put the plastic bag on, the flow CFM dropped to about 167 cfm. I really don't know what they were really trying to prove here besides selling their airfilter system. Anytime you leave your flow bench pulling the same speed and restrict the flow the depression or vacuum as he was saying will go up. I have done this on my flow bench. If I crank the motors up as high as they go and test at .100" lift I get almost 40" H2O and once I get to .650" lift the test depression is down to 12" H2O. Basically that was what he was doing by putting cardboard or the plastic bag over the airfilter.

John


Sat Jul 23, 2011 11:12 pm
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Forget the plastic bag part that was simply a way of showing the pipe was not collapsing as someone on that Colbalt forum was saying it was or might be.

Putting the cardborad over the filter showed you did not need as much filter area as they had to give the same amount of CFM and the larger filter was not a restriction. This simply showed what we have been saying on here for years that flow is presented to your "orifice" from around it's edges and not directed at it. If he would have put the cardboard at the base of the filter it would have shown a loss of CFM in my opinion.

As he stated the airfilter radius was allowing it to flow more air with less depression due to the change of CD. If he would have set the bench for a given depression you would have seen the CFM drop when he removed the filter.

The flowbench was controlling the motors using the set CFM of 300, neat feature to be able to do. When would you be able to use this in testing? Would you need to be able to do this?

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Sun Jul 24, 2011 8:36 am
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I will offer this in regards to using this type of bench.

1. This method will only help when looking for a CFM increase. It will not tell you exactly why you got it. You can potentially raise the DC anywhere in the port to raise cfm or "lower the depression". The problem with this is you may make areas of the port "too fast" for the intended engine.

2. In many cases, a properly shaped/sized port will show no increase in flow or even a decrease. So if a critical area change was done but then the depression goes up (a loss of flow) one might dismiss the potential HP gain and go back to a "flowbench fallacy" that may not show up in HP.

3. One can potentially use a velocity probe. However you would still have to use the same depression and not go by the raising or lowering of depression. This can give you some close cfm values through math, but now you begin to go away from the "floating depression bench"

4. There are many ways to do an induction system in regards to application. Because of this, the floating depression bench will give you different readings. Unless one understands the DC effects through the port, that person will not know what kind of port is being produced.

5. Exhaust ports I feel become trickier when using this method. You can either enlarge many areas to get a drop in restriction or work on the DC of the port having it smaller and still dropping the restriction. Two totally separate ports with 2 different outcomes with the motor. Again, it goes back to airspeeds, areas, and how much flow is needed.

If I had to do a head without a known orifice for cfm. I would use a velocity probe and some calipers using the same depression. A box with motors only and 2 water guages. One for depression and one for velocity. I would then make a mold, get the starting sq/in areas and do a baseline velocity map. Use math to find cfm from that. Then make my changes where needed and retest. If you see a reduction in depression, make note. Then bring depression back up to the test point and probe the port again. Do the math to get cfm values and see where the velocities changes through the whole port. Then if the depression kept falling through all the tests AND, a big AND, your velocity profiles are where they need be, then the port will most likely perform.

My .02$

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Chris Sikorski
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Sun Jul 24, 2011 10:04 am
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Thanks for the explanation Bruce. I see what he was trying to do now and that makes sense after your explanation.

John


Sun Jul 24, 2011 12:51 pm
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Location: central Illinois
Rick- to me this is demonstrating the "inverse" style of testing . with the computer maintaining the ACTUAL cfm of course the depression will go up with restriction.

What concerns me is when testing at a static depression that may be higher or lower than what the engine is seeing at the same valve lift, The flow patterns that develop at that valve lift and that depression around the valve and in the port could be quite different and perhaps misrepresentitive of what the engine will see.

I spose' there is as much ASSumption in what i am saying as anyone elses though. The guy in the video is just trying to sell his intake/air cleaner. two more cents for the pot :)

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Jason


Tue Jul 26, 2011 1:49 pm
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