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mgburchard 
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Location: Tennessee
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 Topic: Attn doc allis
Posted: 20 Mar 2014 at 5:24pm |
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I was over at Ml shop looking at the motor he built for chris. While I was there he said he needed to give you some Venturi info . Per his request . Tsx977 Venturi part number is nozzle 312950 . Price was 28.82 . Big end measures 1.090 small end is .945 . I hope you remember what the discussion was about . Cause he was in one of his moods .
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DrAllis
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Posted: 22 Mar 2014 at 7:53am |
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I've taken notes, but the venturi in question was to a TSX928 which is supposedly a 1 inch small diameter, not .950". They still may be one in the same part. Thanks.
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mgburchard
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Posted: 22 Mar 2014 at 7:41pm |
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If you get a chance look at his build on yt . Titled tn stud
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wi50
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Posted: 10 Apr 2014 at 1:42pm |
Well I rember the venturi discussion. I took a little time today to take some pictures so I can show you boys how to do things the right way rather than take the easy way out.  Both pieces are upside down so you can see what the air has to enter, the venturi on the left is an original one. The one on the right is one I made. You see the step where the venturi would sit on the carb bowl on both. I make it longer to blend into the bottom bowl. This additional length gives me more distance to cut the lead in angles and cut a radius for air to enter the choke point of the venturi. The more gentle the leade in angle the more air a certain size orfice will flow. Every orfice has a coefficient of flow. There's an inlet coefficient and an outlet coefficient. By doing the bowl mods and making the venturi I'm doing all I can to get a better inlet coefficient. The choke point of the venturi has to be where the end of the fuel tube is positioned. The additional length lets me cut lesser angle to get it positioned in the carb correctly.  Here you can see how the original venturi sits on the carb and the sharp corner the air must turn on the top side of the carb bowl to enter the ventrui, it has no room to make that corner and line itself up to the venturi. The flat bottom of the venturi is also seen.
Edited by wi50 - 10 Apr 2014 at 2:19pm
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"see what happens when you have no practical experience doing something...... you end up playing with calculators and looking stupid on the internet"
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wi50
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Posted: 10 Apr 2014 at 2:14pm |
 Here is a modified carb bowl on the left and a stock one on the right. You can see the step where the venturi would sit. I build a big radius out of epoxy and fill in some other areas in order to help direct the air at the venturi. This gives it room and a long gentle radius to follow prior to getting to the venturi. The new ventrui that hangs down into the bowl and has a gentle leade in angle. I file the fuel tube off at an angle to help the fuel enter the airstream.  Here's a better pic of the modified bowl. So an engine will give a "signal" to the venturi. This is what causes fuel to vaporize. If you run to big of a venturi the signal gets to weak and the engine will stumble and fall off. If I simply pull a flow test on a carb with say a 1" venturi and it flows XXX CFM, and if I do the mods to the bowl and make a new venturi it can gain a quick 25% flow for the same size venturi. What does this mean? It means that the air is traveling through the carb better. It means that the signal is stronger at the venturi. The air density is increased. I just eliminated turbulance. The mods increased the inlet coefficient of flow to the venturi. Maybe that engine that could pull a 1" venturi can really now pull a 1.1" venturi, maybe a 1.15" or 1.2" venturi with all other things being equill. It boils down to possiably a 30% to 40% increase in airflow through the carb. Same carb. same engine, less manifold vac, better cylinder filling. There's other mods, turn the fuel pipe OD down so it takes up less area in the venturi. Thin the throttle shaft or make a 1/2 shaft, thin the throttle plate, low profile screws, etc. At times the neck needs to be bored and a new larger throttle plate fit, increase fuel circuits, etc.
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"see what happens when you have no practical experience doing something...... you end up playing with calculators and looking stupid on the internet"
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Steve in NJ
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Joined: 12 Sep 2009
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Posted: 10 Apr 2014 at 2:33pm |
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That mod should increase air speed and density quite a bit! Might be a small benefit shortening the nozzle a tic to put fuel at the lower end of the venturi to add a better mix as it upstairs. What's your take on that? Just thinkin' out loud here...
Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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wi50
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Posted: 10 Apr 2014 at 5:22pm |
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Positioning the "choke point" of the venturi to the fuel nozzle is the tricky part. I try to put it right in the center of the choke point. Putting it higher gives less signal like having a bigger venturi. Putting it slightly lower may just work better. If anything I'd error low rather than high.
It's a guessing game as to what angles to cut to position things correctly and it changes with the size of the venturi. Lets just say I've thrown a few in the scrap barrel.
What would be best is to have a junk carb bowl and modify it to put a tube on, close off the fuel circuit and hook the second manometer on to that tube. This way I could take a depression reading off the fuel tube and see how strong the signal is right on the flow bench. I have 2 manometers on my flow bench and I use one for pitot tube to check air speed at times, or in this instance one could start playing with different things and see what pulls the strongest signal for a given depression pulled on the carbuerator.
A guy can spend countless hours trying things. The first pic in my first post is a simple adapter to space the carb away from the manifold some and allow me to test it as it's normally facing or rotate it 90* and test.... lets just say the air splits to go around the throttle plate and has not yet re attached itself when it has to turn in the manifold. What happens if I turn the carb? Or space it down? Just how can I get better flow through the system and what can I do inside the manifold to help things......Just because a carb flows XXX and a manifold flows XXX and both are good, when they are bolted together the flow diminishes a lot. There's certain things to try and get some of it back.
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"see what happens when you have no practical experience doing something...... you end up playing with calculators and looking stupid on the internet"
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mgburchard
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Posted: 10 Apr 2014 at 5:40pm |
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Why you even fooling with tiny carburetor . You posted yesterday you ran big carbs
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mgburchard
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Posted: 10 Apr 2014 at 5:49pm |
Carb spacer Mitch shown marty back in 2010 
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wi50
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Posted: 10 Apr 2014 at 6:57pm |
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Well I've never seen that pic, and the old saying is true. A picture is worth a thousand words. All allong I was giving you to much credit. I thought you at least knew the basics, but the pic proves otherwise.
I'll explain.....aparantly you can't figure it out on your own.
1. The carb is bigger than the manifold neck.....so you made an adapter. What happens is that the air hits the smaller neck and must speed up. Bright idea, maybe not.
2. The junction from the manifold neck to the manifold. Look at it, it's sharp. There's little to no internal radius to allow the air to turn left or right. There can't be, there's no filler on the outside.
3. Little to no ram pipe to get the air into the carb. Trutr me, it makes a difference.
So, let's speed the air up before it has to turn a sharp 90* corner. That is exactly what the picture shows. Lets send a high velocity stream of air straight uo and try to yank it left or right. Let's try and condense the air so that when the intake cycles overlap and it has to try and finish filling a front cylinder and has to start filling a back cylinder that high velocity stream can't be pulled apart.
Now what you should have done is at minimum is to at least welde the corners up and cut a large radius inside.
I make a new flange and neck and weld this area into a long sweeping radius. I also weld the back side corners. I cut the longest radius I can, then I knock holes in the back side and finish the radius. Fill the holes with a frost plug and cover it up.
Small neck, sharp corners...Yep you left a good 40-50 cfm on the table to get.....more with a custom made neck and more work. Then speed things up to make the corner......it's alright, seeing what I'm seeing here you didn't have enough cylinder head to take advantage of it anyway.
Your immaginary flowbench didn't teach you much. The easy way usually isn't the right way. Stick around though, we've only scratched the surface.......
Edited by wi50 - 10 Apr 2014 at 7:09pm
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"see what happens when you have no practical experience doing something...... you end up playing with calculators and looking stupid on the internet"
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blue924.9
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Posted: 10 Apr 2014 at 7:08pm |
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wi50, are you saying there is an advantage to having the air intake stick out of the hood? or is there a specific direction it has to be pointed to make it better
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hi my names dan, I am a young guy. i have a problem, i prefer my tractors orange and my clutches mechanical, thanks for letting me share
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mgburchard
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Posted: 10 Apr 2014 at 8:20pm |
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Mitch says spacer works a lot like a bbc square port intake bolted to oval port head.
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mgburchard
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Posted: 10 Apr 2014 at 8:34pm |
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Knive edge fools runner into thinking its longer
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Butch(OH)
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Posted: 10 Apr 2014 at 8:47pm |
Ya Pank, Miss match and sharp corners is where it's at when it comes to air flow that why all the top builders started doing it that way on purpose,, 
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wi50
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Posted: 11 Apr 2014 at 8:40am |
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Mg, the other day Mitch (or should I say yourself...I mean yourshelf) was on YT asking for a dyno challenge...of course the moderators on YT have delt with him and rather than block the IP adress they simply delete anything he posts. Sort of sucks for him but anyway..... I suppose he had it coming.
Anyway, I would like to make him aware that his dyno challenge really does exist. It has been scheduled for some time already.
Time: August 2nd
Place: Wilson Machine in West end North Carolina.
So for a meager 6 hr drive those dreams can come true. The chance to prove himeself and his claims in front of people at a social event. A chance to hook to a real dyno allong with other engines with a chance to compare and see how everyone stacks up on the same dyno, same day, etc.
You'll also find that the results will be astonishing. In fact someone who owns and publishes a well known national pulling magazine offered to cover the event. He said "a good train wreck is good for business". So here's a chance to prove yourself.....
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"see what happens when you have no practical experience doing something...... you end up playing with calculators and looking stupid on the internet"
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Hudsonator
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Posted: 11 Apr 2014 at 8:52am |
Well, I'm pleasantly surprized to find a great carb tech thread emerging.
I didn't know anybody else had "beveled" a nozzle tube before. It apparently works great on straight nozzle/emulsion tube combos like the tractor carbs and older antique carbs. I discovered the effect while tweaking up Harley-Linkert carbs. They were notorious for very poor emulsification and nozzle delivery of the emulsified fuel to the airstream.
I'm going to back up Marty's observations about nozzle discharge in relation to the narrowest point in the venturi. Its best to get the discharge surface as close to the exact plane passing through the venturi's narrowest point. That is the point of most efficient vacuum signal transfer to the nozzle. You can get different effects by varying that relationship, but they are only handy if dealing with multiple venturi systems/functions - like a 4 barrel or progressive 2 barrel. Since we don't have that luxury on a single barrel carb - go for as close to perfect positioning in the "choke point" as possible as it is the most efficient spot.
The thing I like about the tractor carbs is they (either by accident or purposely) placed the nozzle/emulsion tube at dang near the perfect angle to maximize a cut on the exit of the nozzle to maximize vacuum signal transfer to the tube. I've found the best angle to be somewhere between 23 and 32 degrees, turned opposite of airflow direction. On the tractor carbs - it works out exactly like Marty's pictures. In a Marvel or Zenith, it means the angle should very nearly match the plane represented by the flat surface of the carb's lower body.
In a Linkert or Weber, the nozzle enters the venturi perpendicular to airflow. But, the same nozzle exit-angle applies and is indexed to be as perfectly opposite of airflow as possible and at the narrowest point in the venturi.
The best answer I can give for why this helps, is more surface area at the exit of the nozzle to expose the interior of the nozzle/emulsion tube to the vacuum signal. Like everything else, there is a limit to how much surface area is "useable" and you can get too much of a good thing. Hence, the 23-32 degree exit angle. These angles are not without application in other areas unrelated to carbs, these are the same angles (varied on conduit roughness factors) cut on culvert entrances to enlarge the entry to a surface area that allows the diameter of the culvert to flow its full diameter at a head equal to its own diameter.
Good bunch of tech by Marty and Steve - please keep it coming!
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There isn't much a WC can't do.
WD's just do it better.
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