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 Post subject: Re: New Builds
 Post Posted: Sun Sep 23, 2012 1:07 pm 
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I think any 3/8 tube can be used, you just may need to turn it down a little. Those are pre-made vents but I have made my own as well like on this 1050.

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 Post subject: Re: New Builds
 Post Posted: Sun Sep 23, 2012 6:13 pm 
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You said the booster outlet sits .400" below the venturi. Thats why its got a high signal. The point of minimum pressure in a venturi is not at the minimum diameter, its past it, its called the vena contracta point.
If you get the opportunity on the flow bench measure and plot the vacuum curve of the booster and then do the main venturi with a probe positioned just to the side of the booster so you measuring as close as you can to the center of the main venturi. The see how the 2 curves overlay onto one another.


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 Post subject: Re: New Builds
 Post Posted: Sun Sep 23, 2012 10:19 pm 
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I plan on discussing this with them, it may have been done on purpose. I do plan to do some booster testing with this body, but looks like it's going to be a bit before that happens. After posting a picture on another forum I had two people interested in trying the carb. It ships out tomorrow to SAM, School of Automotive Machinists, to try on the engine they plan to run at the Engine Masters in a couple weeks. A 406 SB2 head engine that has made almost 860 HP, if it works out to be the best for them they will run it at the Engine Masters. If not, I go back to work. It might be a little large, but the booster characteristics on the boosters I use and the positioning may help, as well as being calibrated as a 2 circuit carb. It will be ncool if they use it, whether they win or not.

Once I get it back I'll see where the best point is for the venturi, and if not this carb I'll build another later and try to move the venturi down to gain airflow without killing too much booster signal, open the venturi diameter in the process. With engine sizes growing dramatically the need for larger carbs is there, the cost for anything larger than a 1250 took a large jump until this one came along. 600+ inch engines are more common, and this fits a lot of them well in airflow ability and with a little venturi work even more airflow.


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 Post subject: Re: New Builds
 Post Posted: Thu Oct 11, 2012 10:55 pm 
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Well I'm in the process of making the changes to see how it responds. Not the prettiest job and I'll probably work it a little more, but I'll do some flow bench testing first.

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 Post subject: Re: New Builds
 Post Posted: Fri Oct 12, 2012 5:25 am 
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Not the best picture Mark but are you opening it up down to the step above the throttle plate?
Thinking your also going to have to modify the legs on the banjo's also as they already stick
out..

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 Post subject: Re: New Builds
 Post Posted: Fri Oct 12, 2012 5:36 am 
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shrinker wrote:
You said the booster outlet sits .400" below the venturi. Thats why its got a high signal. The point of minimum pressure in a venturi is not at the minimum diameter, its past it, its called the vena contracta point.
If you get the opportunity on the flow bench measure and plot the vacuum curve of the booster and then do the main venturi with a probe positioned just to the side of the booster so you measuring as close as you can to the center of the main venturi. The see how the 2 curves overlay onto one another.



Bruce, Can you explain this better as to what issue it has or what Mark is trying to do by doing the mod??

Also the QFX main body weight's a ton and does look like alot of material can be removed from the underside..

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 Post subject: Re: New Builds
 Post Posted: Fri Oct 12, 2012 8:54 am 
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I'm trying to get more air through this 1450 center section, the venturi was put a bit high in it. This makes the booster in the way, killing a little airflow. I just put it down to the tail of the booster like a Holley normally is, I had to take out .055 to do it. I took the picture last night, I'll try to get a better one.


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 Post subject: Re: New Builds
 Post Posted: Fri Oct 12, 2012 11:08 am 
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 Post subject: Re: New Builds
 Post Posted: Sat Oct 13, 2012 1:11 pm 
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Mark , did this carb ever get tested or ran on a Engine Masters motor??


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 Post subject: Re: New Builds
 Post Posted: Sat Oct 13, 2012 2:55 pm 
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Yes, and why it's getting some changes. The biggest is the airflow is way down what it should be for a carb that size, but I think there are some negative effects when the booster tail is not at the venturi point. I'll flow bench test it this next week. And by the way the SAM engine won, a 406 with SB2 heads, with a 2.400 throttle blade carb from Bob Book. BIG CARB!


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 Post subject: Re: New Builds
 Post Posted: Sun Oct 14, 2012 5:26 am 
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Looks like they ran that giant carb through a 4500 - 4150 adapter too , obviously it works !
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 Post subject: Re: New Builds
 Post Posted: Sun Oct 14, 2012 6:19 am 
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[quote="jmarkaudio"]Yes, and why it's getting some changes. The biggest is the airflow is way down what it should be for a carb that size, but I think there are some negative effects when the booster tail is not at the venturi point.






Mark does the Dominator have the same issue??? Have you flow tested any of them and compaired those #'s to
an HP or your shoot out carb winner??

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 Post subject: Re: New Builds
 Post Posted: Sun Oct 14, 2012 8:46 am 
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We logged airflow and booster draw with several bodies and different booster arrangements. I've also looked at the QFX 1050 I have and it's not the same, the Venturi is in the correct spot. Holley's are fine.


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