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Which means "Evil Twin". Lets see your projects where you change boring into fun or create the fun from scratch.
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PostPosted: Thu Apr 11, 2019 6:16 am 
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So, I have a Carburetor Comparator and I have used it years ago to just compare small carbs as it was designed to do and it did ok. I am thinking of trying to convert it to have actual CFM data and not spend a lot doing it. Any ideas would be helpful. I am sure there will be a lot of questions and I will answer as best I can. I am interested in flow testing a set of VW heads I am building for a Dune Buggy engine upgrade I am doing.


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PostPosted: Thu Apr 11, 2019 7:18 am 
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I have never seen one of those...do you have a link to any info on it or have anything you can post so we can maybe figure out what's in it?

The simple fact that it can compare flows means its measuring flows and all you need to do is calibrate it which is not too hard, but I'd like to understand a little bit about what exactly it is before jumping to calibrating it.


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PostPosted: Thu Apr 11, 2019 12:18 pm 
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Just an Idea I've been pondering: Use a hot wire mass airflow sensor. Hook it up to an Arduino and a digital display. I think most of them now cost under $50 and have a digital output, but even if they are analog the Arduino can accept either input. You can probably cobble the whole thing together for under $100.


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PostPosted: Thu Apr 11, 2019 8:37 pm 
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I had the same thought as i was dragging my bench around and pondering upgrading it....then decided I didn't need another project :lol:

I've never arduio'd anything....there is a mega board in my printer but I didn't set it up.....I'm sure we could figure it out though. Flow is volumetric flow not MAF so you need to add a temp and Baro sensor to do the conversion I guess. Probably want flow straighteners above and below it, buy the pipe...adapters for the head, controller for the shop vac(s), better vac motors if you want 28"......its probably more like a $500+ project by the time its working.


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PostPosted: Fri Apr 12, 2019 6:22 am 
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Here is what I know about it. The motor is mounted in the divided partition in the middle. It has variable speed. column tube on the right is plumbed to the intake side of the box and the inches W.C. gauge is plumbed to the left side or the exit flow side. There are flow control valves on top. The fan is not reversible so exhaust flow is another issue. I have a second motor and could mount it flowing the other way maybe. It may be more trouble than it is worth to try and convert this thing. I just don't know yet.

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PostPosted: Fri Apr 12, 2019 8:00 am 
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For exhaust you can put a short piece of pipe on the head and connect that to the bench. pressure in the cylinder or vacuum in the pipe are pretty much the something flow wise. Then you bolt the head to a cylinder and add a quick clay stack to the case end of the cylinder and you're flowing exhaust. Mine is really not designed well to convert either....but its possible.

Do you have a brand or model for anything for it that I could google?

The unit as it is will certainly tell you if you are making the flow better, you just won't have numbers with units. To get units you need to calibrate, to calibrate you need something of known flow, that something is an orifice plate. I have no idea how much it costs to buy a set, but you can make them easily enough and the flow comes from here:
https://www.efunda.com/formulae/fluids/ ... wmeter.cfm

I cal at 0, 67, 131, 171 @10" which is about 0, 115, 226, 295 @28"

I'd have to check the dimensions I used..they were round numbers IIRC and I sized my stuff around the max flow I expected from the heads....I was shooting for 160 and got 156. (@10")

I put the plate on and measure the flow, the manometer reading goes into excel, excel gives me values for an the equation of the line that goes through the points and I plug the equation values into a table calculator so I had a calibrated table I can look at to convert my manometer readings to actual flow values. When I'm on the bench I work directly in manometer readings, more is better and once the development is done I know exactly what readings I'm looking for to match the other ports to the 1st.....so the cal table just tells me what to plug into dynomation and lets me make a pretty graph to post on the forum :)

I do a cal every day with the plates or with the head I'm matching. When you do it this way you really don't need to worry about temp or baro, it washes out in the cal.


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PostPosted: Fri Apr 12, 2019 10:51 am 
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I have the "instruction" manual. I had to give the maker the serial number to get it. I'll scan it and email it to you. There is a thread on a flow bench forum where a guy bought one and had an issue getting the manual too.
http://www.simonsbalancing.com/carbcomparator.html
this is the page from the company that made it years ago. I think they stopped making them many years ago I think in 2000.

http://www.flowbenchtech.com/forum/view ... =39&t=1005 here is a link to the page discussion.

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PostPosted: Fri Apr 12, 2019 2:50 pm 
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hmmmm...it jut occurred to me that if its for gokart carbs, like the 8hp (at most) brigs engine in the photo...that's like 20cfm @10" or 12 @28". That might be your biggest problem. You can alway flow at less pressure to get in range but you might end up flowing at 1 or 2" on a system designed for such small stuff.

Maybe its worth just cobbling up the head to the machine and see what pressure maxes out the readouts before you spent a lot of time setting up and calibrating?


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PostPosted: Tue Apr 23, 2019 6:31 am 
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After a lot of thought and research, I have decided to just buy a flow bench. I found a very nice unit with all the whistles and bells.
Here is a link to the flow bench in use.

https://www.youtube.com/watch?v=N-J-XmzaZt4&t=11s

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PostPosted: Tue Apr 23, 2019 10:26 am 
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Any day you can convince yourself you need a new tool is a good day :)

I didn't here him day what the bench is exactly? Did 8 miss it?


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