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 . . .

Here are most of the parts and pieces . . .

http://anthonyrawson.com/Cars/Tools/FlowTestKit0.jpg

The initial flow test . . .

http://anthonyrawson.com/Cars/Tools/FlowTestKit1.jpg

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.

http://anthonyrawson.com/Cars/Tools/BandSaw.jpg

Here I am getting ready to do a test head flow to make sure it will be worth building.

http://anthonyrawson.com/Cars/Tools/FlowTestKit2.jpg

Here is the first flow test in progress.

http://anthonyrawson.com/Cars/Tools/FlowTestKit3.jpg

There are the little plastic flow stabilizers I made to straighten out the flow passing into the measurement tube.

http://anthonyrawson.com/Cars/FlowBe...owTestKit5.jpg http://anthonyrawson.com/Cars/FlowBe...owTestKit6.jpg

A look down the completed flow measurement tube.

http://anthonyrawson.com/Cars/FlowBe...owTestKit7.jpg

And the complete flow measurement unit.

http://anthonyrawson.com/Cars/FlowBe...owTestKit8.jpg http://anthonyrawson.com/Cars/FlowBe...owTestKit9.jpg

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.

http://anthonyrawson.com/Cars/FlowBe...wTestKit10.jpg

http://anthonyrawson.com/Cars/FlowBe...wTestKit11.jpg

http://anthonyrawson.com/Cars/FlowBe...wTestKit12.jpg

And finally, a pic of the whole shebang.

http://anthonyrawson.com/Cars/Tools/FlowTestKit13.jpg

And a close up of the cylinder/head set up

http://anthonyrawson.com/Cars/Tools/FlowTestKit14.jpg

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

http://anthonyrawson.com/Cars/Tools/FlowTestKit15.jpg

And a shot down the test flow tube

http://anthonyrawson.com/Cars/Tools/FlowTestKit16.jpg

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.

I already made something to provide a consistant and even flow into the ports. Check out the last few pics.

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.

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.

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

What is the conversion from 25” to 28” of H2O if you don’t mind?

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

I was not aware of a conversion for that.

Thanks

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.

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.

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.

I am not too concerned about getting exact CFM numbers or pumping a lot of air through the ports. I just want to make sure that the heads and manifold will flow the same amount of air through each port so that my A/F ratio is consistant across all the cylinders.

I know that I may not be able to create the turbulence that could be an issue at higher revs but between the machining, port matching, removing all casting roughness and good blending work I would be willing to bet that the heads are pretty well matched.

Despite the clean up work I have already done to it I suspect my carrera manifold will be a different story though.

I do have another shop vac so for the sake of science I might put a T in the plumbing and see what I get with double the flow though.

Do you have any referances to why there would be turbulance at 28" water vs 10" water? I would suspect the same relative turbulance at both pressures. I haven't seen any myself or have I measured any difference. My suspicians would be a problem with the equipment.

Check out the following links
http://www.superflow.com/support/support-flowbench-faq.htm

http://www.superflow.com/support/support-flowbench-works-how.htm

http://www.superflow.com/support/support-flowbench-which.htm

And finally an explanation of the ammount of error that you might get at much much higher test pressures, Note it should be less than 1%, which on almost any home made bench would be more than wishful thinking.

http://www.superflow.com/support/support-flowbench-what-best-test-pressure.htm

With your engine running at 240" of water and you testing at 10" or 28" whats the difference?

The faster flows at higher vacuumes are more likely to cause the flow seperations and disturbances that cause turbulence.

The problem I have seen only shows up in 2 or 3 heads out of 100. Usually it can be fixed with some attention to the short turn radius.
Its my belief the higher velocity seen at the higher pressure drop
can cause the air detach from the boundry layer and tumble.
The interesting thing is at higher valve lift the flow comes back in line.
I have a 2 freinds with the SF110 flowbench. When they see a slight oscillation on the manometer on thier bench (@ 10"), and I test the same head on my SF600 (@ 28") the oscillations are dramitically multiplied.
FWIW My bench calibrates within .2 % of the setting when it left Superflow in '92. I have also tested an orifice plate on mine and 2 other SF600 benches in the SF Bay area and all 3 benches were within 1%. Flowbenches are like chassis dynos... They are best when compared against themselves and not compared to a bench or a dyno 1000 miles away.

Well, if I adjust my single test run up to 25" of vacuum I get about 180 CFM of flow through 0.4" of valve lift and my TP tube entry flow stabilizer.

Does anyone have any other 911 flow numbers at 0.4" of lift to compare that to?

http://forums.pelicanparts.com/showthread.php?s=&threadid=155158&highlight=snowma n

Your within 7 cfm. ie 190 vs 197
Try the clay, see pictures.

also see

http://forums.pelicanparts.com/showthread.php?s=&threadid=100664&highlight=snowma n

Well, I had a chance to test the bench this weekend and it was very consistent. Between switching between heads and running the bench for different amounts of time it always produced the same results. As soon as I get back from dinner and visiting my daughter I will post the head flow results on my rebuild thread later tonight. :D

If my calculations are correct my intake port flows are phenomenal.

I think that the value of your flow bench is not to determine if your heads have "phenomenal" flow, but rather if they flowed better or worse after you have made any changes to them. To determine if the heads have "phenomenal" flow you'll need to compare them to a set of stock heads -- which you may or may not have done. But it's not clear from your posting if this is the case.

I took one before measurement and have calculated a flow improvement of almost 40%.

My current calculated flows of >255 CFM @ 25" vacuum and 0.45" valve lift are also very respectable.

Compared to other numbers I have looked at thats about as good as it gets for head with 49mm intake valves.

The CFM numbers may vary depending on the equipment used and what is used to guide the flow into the port but this whole experiment was all about making sure the head flows were evenly matched.

I am happy to report that all the heads except one are within 1% of each other, and one is about 1.5% off from the rest.

I will be looking to see what is different about my oddball so I can try to correct it.