Cascade Crew

blue89 · Posted: Wed Apr 18, 2007 11:19 am Post subject: Flowbench DIY!

Found this, had to share!

http://en.wikipedia.org/wiki/Air_flow_bench

and it led me to this

http://www.ag.auburn.edu/users/gparmer/articles/flowbench2/

Flowbench Forum

http://www.tractorsport.com/cgi-bin/forum/cgi-bin/ikonboard.cgi

Shop Vac Flowbench

http://www.diyporting.com/flowbench.html

I'm building one! I have a large squirell cage fan (10,000 cfm) that i think would work. I'm all about it! Especially sice I'm mister tinker.[/url]

Dewey316 · Posted: Wed Apr 18, 2007 11:24 am Post subject:

Cool. I was going to buy a few manometers. You can get several of them on ebay for almost nothing. I was going to drill holes in my spare hood, and use it to do a pressure map for the front of our cars, so I could design the venting for a hood, and a front splitter.

blue89 · Posted: Wed Apr 18, 2007 12:59 pm Post subject:

Buy a manometer? You're crazy. All you need is fish tank tubing, a board, and some water.

When I measured my intake vacuum I did it with an open ended u-tube manometer. You can do closed end manometers for more pressure but I forgot how to calculate the pressure.

Dewey316 · Posted: Wed Apr 18, 2007 1:03 pm Post subject:

but when I am driving in a car, at speed, a quick check of the gauge would be nice. They are only $10-$15 a peice.

blue89 · Posted: Wed Apr 18, 2007 1:08 pm Post subject:

no kidding. Thats cheap. How accurate are they? I have a cool fancy one that measures 0-120psi with .01 psi accuracy.

Dewey316 · Posted: Wed Apr 18, 2007 1:27 pm Post subject:

What you want is a Dwyer Magnehelic guage, it measures pressure diffrences, so you can compare the change verses atmo pressure.

The one I pulled up was a 0-1" h2o gauge, it said accurate to +-2%, that would would make it accurate to .02" h20, which is about .036psi. so that would make that gauge accurate to within .0007psi. They have diffrent gauges all of them seem to be in the +-2% range. Just do the conversion from inches of h2o to psi conversion, to find one in the range you need.

Here is the link....
http://cgi.ebay.com/Dwyer-2001-Magnehelic-Differential-Pressure-Gage-0-1in_W0QQitemZ150112331054QQihZ005QQcategoryZ55825QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

blue89 · Posted: Wed Apr 18, 2007 1:37 pm Post subject:

dude. 1" of water is hardly anything. I can blink 1" of water (completely uncomparable, but still). Do they have any with a larger scale and same precision?

I would need at least 1psi or 28" water for the suction side of the flowbench, but then a smaller one for the actual head pressure drop.

Dewey316 · Posted: Wed Apr 18, 2007 1:41 pm Post subject:

Yeah, it was just the first one I clicked on.

They have them in all sorts of diffrent stuff, including PSI reading (i saw a 0-15psi one listed), along with many diffrent scales of inches of water.

better link...

http://search.ebay.com/search/search.dll?from=R40&satitle=Magnehelic

Here is a 0-50 inches one.

http://cgi.ebay.com/DWYER-INSTRUMENTS-MAGNEHELIC-PRESSURE-GAUGE_W0QQitemZ250104139540QQihZ015QQcategoryZ55825QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

blue89 · Posted: Wed Apr 18, 2007 2:09 pm Post subject:

Good stuff. I think I'll stick to water u-tubes though. Low tech I know.

Sounds like those gauges will be perfect for what you need. Have you ever measured the pressure developed in the headlight pocket? (Maybe you should start a new thread on this topic, hijacker Very Happy

)

Dewey316 · Posted: Wed Apr 18, 2007 3:33 pm Post subject:

Sorry, I haven't done any mesurements yet, before I put a new hood and nose on, I drill holes, and start measureing this stuff. Very Happy

blue89 · Posted: Thu Apr 19, 2007 7:09 am Post subject:

I don't think you have to drill holes man. You might be able to use fish tank tubing with a small green bubbler on the end. Just tape the bubbler on the various locations and take a measurement. The bubbler should be able to deflect any incoming air from skewing your measurement.

Dewey316 · Posted: Thu Apr 19, 2007 8:11 am Post subject:

yes, but I want to pressure map the front of the car, so I want to be able ot measure pressure drop or raise across the surface, so i need to mount it flush @ 90*.

blue89 · Posted: Thu Apr 19, 2007 8:40 am Post subject:

Well, what mph do you want to make measurements?

1psi = 27.7" H2O
1" H2O = .036psi
(just for those that don't know)

The last time I calculated frontal pressure, I got 0.07psi across a flat object moving into the wind at 70mph. That would be 2" H2O.

I wouldn't try to measure the entire front, just the pockets, cowl, air intake area, rad, and engine bay. Are you really going to go all out? Remember that any changes in car stance will change all your measurements.

Dewey316 · Posted: Thu Apr 19, 2007 9:25 am Post subject:

Yes I know. I am really interested in the hood, although I can tell you what the text books say should happen, I would like to really know where the lowest pressure across the top of the hood is. I idealy then I can use those to vent the radiator and unhood pressure, to try to keep the car from floating at high speeds.

Remeber, the goal and plan for my car is to run silverstate and work up to doing a pretty high rate of speed. (My goal is to hit the magic 200mph mark at some point). Getting to that kind of speed, you really need to start sorting out the aero stuff.

blue89

I completely agree. Are you going to do under chassis aerodynamics? I like what the Grace people did to theirs.

Dewey316 · Posted: Thu Apr 19, 2007 10:12 am Post subject:

at those speeds, undercar aero is HUGE. I have seen that pic, I also plan to look at cars down there, and see what they are doing. I imagine that the guys that are going really fast, are doing full undertray's, not just under the engine. But done right, using the engine undertray to also suck air out of the engine bay would help.

Maybe we need to start a thread on DIY wind tunnels Very Happy

I wonder if Brandon would let me build something in his barn. putting the car on some 4 corner scales, and blowing wind over it at 120mph would be some very nice data to have.

blue89 · Posted: Thu Apr 19, 2007 10:30 am Post subject:

Back to flowbench stuff.

The instruction set linked above lists that there is a logarithmic style scale for calculating airflow percentage. This seems to be based on a change in pressure drop across the calibrated oriface.

To operate the flowbench for head intake flow:

1. Turn on the fan
2. adjust so the machine sucks
3. turn the calibrated oriface to the correct size (slightly larger than the max cfm expected to flow through the head)
4. adjust fan airflow until the oriface psi drop is 28"
5. attach head to flowbench
6. measure the change in psi drop (should be less drop).

If the head flows the same flow as the oriface, then the psi drop across the calibrated oriface will be half since the restriction is basically doubled.

So could you then use the same equation for voltage drop across resistors to calculate the airflow of the test piece?

Dewey316 · Posted: Thu Apr 19, 2007 10:53 am Post subject:

It sounds like this would be great for comparisons, say for example, stock heads, then ported stock heads. I don't know if you will be able to accuratly measure the actualy flow.

Hmm, wonder if you could hook a volt meter up to a stock MAF, and use it to measure the airflow for you...

blue89 · Posted: Thu Apr 19, 2007 11:37 am Post subject:

They don't have the precision. I've looked into it all ready. Measuring a 10% change would be difficult.

Sellmanb · Member Joined: 30 Nov 2004 Posts: 727 Location: Tigard, OR

the best use for this machine would more than likely be before and after comparisons. Who knows how accurate it would actually be, but w/ a before and after spec, even innacurate, you get a good idea how much flow was gained, not neccesarily (sp?) how much flow there is. Nice link and good read btw Smile