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Cool DIY Flow Bench

Since its time to start measuring and adjusting port flows I just completed a little fabrication project I have been working on for the last couple of months. A trip to lowes for some plumbing and some dumpster diving at the plastics store near where I work have provided me with all the materials I needed for this little frankenstein project.

Grand total for everything I had to pay for, $30.

At the heart of my beast is the cannibalized turbopump from a 1.25 HP shop vac.

The first thing I did was build a basic flow measurement tube to measure the maximum amount of air this thing could move. If it couldn't flow more than a hundred CFM it would be useless for testing my ports and manifold.

Fortunately my home made water manometer registered a dynamic pressure of about 4.8" of H20 which represents an unrestricted flow of about 200 CFM through the 2" test pipe. Thats should be enough to test and and match the ports on my 930.

When I first rigged a head up to the flow tester before doing my port work it was flowing about 150 CFM through the intake port with 0.4" of valve lift and 14.8" of H20 draw.

With the intake ports opened up to 40mm I am now drawing about 158 CFM using only 8" of vacuum @ 0.4" of intake valve lift.

This is just preliminary data but I will be spending the next few days running a few tests to determine how precise this thing is since measuring relative flows between ports is its primary function. I am too lazy to calculate the exact flow effects of viscosity in the measurement tube, so any CFM calculations could be several percent off.

I know you guys like pics of projects, even the strange ones, so enjoy . . .

Last edited by 350HP930; 03-27-2005 at 09:57 PM..
Old 03-27-2005, 09:37 PM
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Here are most of the parts and pieces . . .

Old 03-27-2005, 09:38 PM
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The initial flow test . . .

Old 03-27-2005, 09:39 PM
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I needed to cut a lot of pieces for the flow bench not to mention the custom bracketry and plumbing I will need to make for the 930 so I spent $87 at lowes on a new tool for my shop.

Old 03-27-2005, 09:42 PM
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Here I am getting ready to do a test head flow to make sure it will be worth building.

Old 03-27-2005, 09:44 PM
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Here is the first flow test in progress.

Old 03-27-2005, 09:45 PM
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There are the little plastic flow stabilizers I made to straighten out the flow passing into the measurement tube.

Old 03-27-2005, 09:47 PM
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A look down the completed flow measurement tube.

Old 03-27-2005, 09:48 PM
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And the complete flow measurement unit.

Old 03-27-2005, 09:49 PM
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And a flow bench needs a bench so I made one out of plexi. Now all it needs is a big hole and a few more pieces of scrap plexi.





Old 03-27-2005, 09:52 PM
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And finally, a pic of the whole shebang.



And a close up of the cylinder/head set up



And a close up of the home made manometer pressure gauges.



And a shot down the test flow tube

Old 03-27-2005, 09:54 PM
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A trick to even out the flow into the head port without the intake attached. Use modeling clay, the same kind you used in kindergarden. Roll it into a 1-1/2" to 2" diameter cord. Wrap the cord around the intake port and then blend in the clay to the port. This provides a smooth radius and a more accurate picture of the port flow than without it. The diffenence can be as much as 10 to 20% depending on the port. Same for any opening that has sharp edges. The flow will also more closely match the flow with an intake attached.

For absolute numbers see previous data I have posted. Most accurate is with valve full open for cal purposes. These numbers from differen't shops will typically agree withing 1 or 2 cfm! I used a calibrated Superflow 600 bench for my numbers.

I just noticed the clothespins, cool. I usually use a tru value spring that is very light for a valve spring and a dial indicator with a screw to set the valve opening.

Last edited by snowman; 03-27-2005 at 10:50 PM..
Old 03-27-2005, 10:16 PM
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I already made something to provide a consistant and even flow into the ports. Check out the last few pics.
Old 03-27-2005, 10:22 PM
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I see it. But the clay method is more consistant with practice.

Very nice setup by the way. I used a shop vac for my own home brew setup. Made a couple cal orfices that I measured on the Superflow 600 to cross check with. Manometer is similar. Although I did use a classy wooden rule pasted to the back of the manometer. Your workmanship is excellent, very very nice job.

Another practical hint. Use a couple of drops of antifreeze in the manometer. Color helps readings and looks cool. And for the less fortunate of us keeps the thing working for more than 2 months out of the year.

Last edited by snowman; 03-27-2005 at 10:43 PM..
Old 03-27-2005, 10:29 PM
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The data that I have shows that both the early S heads and the Turbo heads flow up to 230 CFM stock. You might need a second vacuum motor.
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Old 03-28-2005, 06:37 AM
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You will have to convert the data from your pressure drop up to 25" or 28". I have the formula if you need it.

Here is a really slick set up . I have tested 2 heads from 2 different customers who have this set-up and both are within 1% of my Superflow SF-600.
Best part is the price is $1000's less than the professional benches and just as accurate.

http://www.audietech.com/FQPics.htm
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Old 03-28-2005, 08:26 AM
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What is the conversion from 25 to 28 of H2O if you dont mind?

For instance what is 218.27cfm @ 25h2o @ 0.499 lift converted to 28 of h20?

I was not aware of a conversion for that.

Thanks
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Old 03-28-2005, 09:35 AM
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Multiply the cfm at 25" by 1.06 to get the cfm at 28"
If you have cfm at 10", multiply by 1.58 to get cfm at 28"

If you need a larger motor for the homemade flowbench try Grainger. I have seen some nice ones at a reasonable cost.
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Old 03-28-2005, 10:57 AM
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The formula for converting flow at a lower pressure to a higher pressure is determined by the following ratio:

Flow at high pressure/flow at lower pressure= sqrt(high pressure/low pressure)

Using this relationship you can flow a head at any pressure you want to and convert it for comparason to any pressure you want. Some people do not beleive in math or science so they insist on using actual flows. Also 1200cfm blasting thru something is always way more impressive than 200cfm.
Old 03-28-2005, 11:39 AM
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The problem converting to a higher pressure drop is turbulence. Some ports will become turbulent at a higher pressure drop. I have tested heads at 10" and done a back to back test at 28". Sometimes this works fine , other times the port goes nuts and the airflow drops.
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Old 03-28-2005, 12:39 PM
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