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experimental venturi fabbing
https://www.slantsix.org/forum/viewtopic.php?t=14592		 Page 2 of 5
Author:  panic [ Mon Oct 03, 2005 11:18 am ]
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The general trend has been to get the most strong and "linear" signal with the least disruption to the flow around the booster and least reduction in CFM.
Note from certain 4500 Holleys and Weber DCOEs that a long booster suffers less from reversion pulses in IR applications.
Remember that the tail of the booster should (theory) end about .030â€￾ down-stream of the minor diameter of the main (original) venturi.
I have a feeling that annular is only a trade-off against conventional because annular (as currently manufactured) requires added thickness at the discharge opening which reduces CFM more than the less intrusive downleg etc. but is easy to produce as 2 castings (pressed together) with minimal machining.
I think an annular could be made to mimic proven conventional (low loss) shape and still incorporate radially symmetrical discharge with no flow loss - it just takes a lot of hand work.
You can buy annular boosters from Summit etc. Special order the Holley 4010 booster, available as Holley “Secondary Nozzle Bar Assemblyâ€￾ (Part Number 1021-837-11A), which is a casting containing two boosters, easily separated with a razor saw, Dremel, &c. Each measures 19/32â€￾ (.594â€￾) ID, and ⅞â€￾ (.875â€￾) OD.
Author:  panic [ Mon Oct 03, 2005 11:29 am ]
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BTW: despite the magazine's "new" and "secret" description, here's a booster (not annular - the small hole is for the discharge tube, not shown) and main venturi insert of a 1 barrel that's been around for a while.

Image

Anyone guess what it's for, and how old?
Author:  Dart270 [ Mon Oct 03, 2005 12:42 pm ]
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Model A? Looks pretty old and maybe ferrous metal?

Lou
Author:  panic [ Mon Oct 03, 2005 1:39 pm ]
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Harley 1941
Author:  argentina-slantsixer [ Mon Oct 03, 2005 3:02 pm ]
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I'm a li'l bit in between of confused and overwhelmed :lol:

So, Lou (and the article) says that the top should be at the narrowest point of the carb barrel (where the pressure is low ans the velocity is high)
But Panic sez that the end should be .030 downstream this narrow point.... hmmm that leaves me with no "wing"section at all... :?
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I have a feeling that annular is only a trade-off against conventional because annular (as currently manufactured) requires added thickness at the discharge opening which reduces CFM more than the less intrusive downleg etc.
So do I, in fact, I'm willing to fab the thing cuz the annular ones I saw in pix provided by... (steponmebooom or D.Idiot? CRS) Was thick and restrictive looking.
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The height of your venturi in relationship to the existing throat...While you're fabricating, come up with a way to adjust the height...
You mean, ditto Lou, the relative position in the carb's barrel? I see...

I have another question: what if the booster venturi is so large that most of the airflow passes thru it, but think enough to be non restrictive? I had this crazy idea while looking at panic's harley 1941 design: the top of the difusor (barrel) on the carb can be machined out to carry the fuel inside the narrowest point, all around the barrel, and have 6, 8, whatever simmetrical discharge holes drilled on it... This way you use the main venturi (the barrel) as the booster itself, and cut off restrictions (I mean, you kiss goodbye the thick leg that connects the booster to the wall) but that would require major machining (not so difficult) and all the air going on the inside of the booster itself (this is the thing I don't know if it's reasonable-suitable)
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I'm a li'l bit in between of confused and overwhelmed :lol:

Now I'm getting a little excited :mrgreen:
Author:  emsvitil [ Mon Oct 03, 2005 7:58 pm ]
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And make any leg that is in the air flow airfoil shaped not round for the least amount of drag...... Ideally an airfoil shape won't have any net effect on flow................



Wonder if you should make a bench model (with clear pieces even) so you can see what happens and measure pressure differences....................
Author:  Ice Titan [ Tue Oct 04, 2005 11:51 pm ]
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And make any leg that is in the air flow airfoil shaped not round for the least amount of drag...... Ideally an airfoil shape won't have any net effect on flow................
Could he possibly angle them such that they force the airflow to twist in one direction? I don't know that this would help any at this point. I tend to think such fins in air intakes and throttle bodies are mostly snake oil. But what could it hurt to try?
Author:  emsvitil [ Wed Oct 05, 2005 12:20 am ]
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You've got to love this backseat fabricating...................

:twisted:
Author:  GTS225 [ Wed Oct 05, 2005 4:50 am ]
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Ya know.....it occurs to me that if he makes them out of steel or iron, and magnetizes them, they'll work like those "molecular alignment" magnets that's supposed to get you a bazillion mpg. :? :oops: (Sorry, couldn't resist)

Roger
Author:  argentina-slantsixer [ Wed Oct 05, 2005 7:48 am ]
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Quote:
Ya know.....it occurs to me that if he makes them out of steel or iron, and magnetizes them, they'll work like those "molecular alignment" magnets that's supposed to get you a bazillion mpg. :? :oops: (Sorry, couldn't resist)
Roger
Mjuaaaaaaa¨:lol:

About the wingfoil shape of the leg itself, could be made, in fact, as long as I'm fabricating I can get away with almost anything I can think of AND get done.

Ice titan: about twisting the airflow in one direction (aka creating turbulence) if ain't too much flow restrictive is good for low end and ain't hurts the top end (I remark the non-restrictive thing). Our 1922 had a funny venturi (I don't know if your 1920 has the same...) it's like a wall to wall leg (airfoil shaped and then something like an H where the discharge holes are in the middle and the high and low parts of that H are plain old flaps. One old trick I've been thaught is to bend those flaps to produce a swirl. Gives crisper throttle response. You can say that's snake oil, but if you know your car you can feel the difference as little as it is.

So bottomline I think that my setup would look like this:

Image

No one has given any opinion bout using the throat venturi as the booster... I don't know if I'm explainig myself correctly...

would be like this:
Image
Author:  emsvitil [ Wed Oct 05, 2005 7:59 am ]
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The throat body wouldn't have enough pressure differential to work well at low throttle................ might work at the high end.


Also you might get an effect of the fuel droplets clinging to the throat rather than enter the air stream (a booster eventually ends and the fuel has to enter airstream)
Author:  panic [ Wed Oct 05, 2005 8:14 am ]
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I don't think you understand the purpose of the booster. What you drew will probably have an effect, but it's too low, and blocks (reduces) the main venturi - which is exactly what using a booster (rather than a smaller venturi) does not do.
Author:  argentina-slantsixer [ Wed Oct 05, 2005 8:15 am ]
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The throat body wouldn't have enough pressure differential to work well at low throttle................ might work at the high end.
So @ larger booster size = worse low end response... I get it.

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Also you might get an effect of the fuel droplets clinging to the throat rather than enter the air stream (a booster eventually ends and the fuel has to enter airstream)
Didn't think of that.... :?

What do you think about the tall - downlegged one?
Author:  argentina-slantsixer [ Wed Oct 05, 2005 8:23 am ]
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this reply from me was mildly snappin at panic's suggestion that I didn't understand (and I didn't by the time) how this thing works.
Author:  Dart270 [ Wed Oct 05, 2005 1:57 pm ]
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I believe the booster opening (top in your pics) needs to be at or near the same height as the narrowest point in the main throat venturi, otherwise you get no boosting.

Lou
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