MSD bench mods

[JRM]

I see alot of people saying the MSD bench is off on its flow plate specs. I made a copy some time ago. I was thinking of modifying the one I built and wanted some input.
What I was thinking of doing was instead of using the ora plate with different cfm holes just making 1 4" hole and doing the same at the top of the bench where the head fixture would mount.
I am still trying to figure out the formula for cfm through a 4" hole. And how many vacc motors I will need.

[larrycavan]

Unless I misread your post, you're intending on using a single 4 inch hole. If that's the case, you won't find a single hole of that size to provide you with the accuracy you'd want. If you're going to be flowing car or motorcycle heads, you'll end up with readings on the low end of the inclined manometer scale. You always want to be flowing with an orifice size that give you readings above 50% on the scale.

[84-1074663779]

As Larry says, the flow scale is non linear, at the low end the numbers are compressed so much that the reading accuracy falls away very quickly.

It is probably only practical to read a manometer between about maybe 25% and 100% of the sale length. That covers a 4:1 pressure range which would be a 2:1 flow range.

So each orifice is usable only over perhaps a 2:1 flow range. How many orifices you end up requiring depends on the total flow range you plan to cover. Four orifices would give you a 16:1 range. seven orifices a 128:1 range and so on.

If you want to measure flow at very low valve lifts, and I am sure you will one day, the CFM that needs to be measured will not be high.

Much better to have a very wide selection of available orifice sizes, and always keep the flow up in the top half of the manometer if you can. The flow scale graduations up there are further apart and reading accuracy will be better.

[larrycavan]

If I were building my bench over I would make the following changes. Look at a Superflow 600 as compared to the MSD design. The superflow 600 has a raised section on the top over where the flow disk is on the MSD. The MSD has the hole cut right over the flow disk. What I'm adding to my flow bench is that top rectangular section for the head fixture to mount on rather than directly over the flow disk plenum. Rather than cutting a hole right over the flow disk, I will seal mine there and cut a long, narrow, rectangular hole in the original MSD top, toward the front. This will put the flow path away from being directly over the calibrated flow disk. I will cut the 4" hole in the top rectangular section that I add on. The air moving past the flow disk should be less turbulent. I will mount my static pressure tube about 1" below the hole in the new top section with a little bracket that keeps it at a true right angle to the flow through the head fixture as well. Now this may decrease the flow pressures but I flow at 10" anyway rather than 28".

If I were to make a new flow disk, I would not use multiple holes on any section of the flow disk.

I bought a flow calibration plate for a 110 model directly from Superflow. I have calibrated all my flow ranges with it. For the price, I figured it was worth it to have a little peace of mind. That's something that didnt' come easy when I was trying to understand how the thing worked.

I might add that some of the posts I found on this web site have been very good help. I wish it was around in 1993 when I built my flow bench.

If you can find someone with a superflow flow bench and get them to allow you to copy their manual that came with the flow bench, it would be a good thing to have around. I was fortunate enough to have a friend with a 110.

Larry

[Thomas Vaught]

All of the Super Flow 300/ 400/ 600/ 1200 benches use a flow
deflector plate directly under the discharge hole. The air must
go around this plate (the plate is about 1/2 the width of the bench).

It is centered in the cavity about 1/2 way between the discharge hole and the orifice hole. It is attached to the bench with 4 tabs.

I am surprised that no one ever mentions this plate when they describe the 300/400/600/1200 benches.

It totally eliminated a direct shot of air from the discharge hole to
the orifice hole.

Hope this helps.

Tom V.

[larrycavan]

Tom,

Thanks for filling in that little piece of the puzzle.

You mention the plate being about half the width of the bench. What is the front to back [depth] aprox. dimension?
Does the deflector plate run the full depth of the flow bench? If so then the airflow path would be from two directions toward the flow orifice. The air would hit the deflector and move left or right, bend down and approach the flow orifice from two directions.

In order to minimize turbulence, I was leaning toward the air coming from the discharge hole then moving forward toward the front of the bench, passing down into the flow orifice plenum through the long narrow rectangular opening I described in the previous post and then flow back toward the flow disk opening from a single direction.

I'm picturing the flow to be smoother coming from a single direction than it would be coming from two or perhaps 4 directions as it flows over a deflector plate. The number of directions being related to if the deflector plate runs the full front to back dimension of the plenium. What are your thoughts on this?

Larry

Larry

[larrycavan]

I whipped up a quick drawing with paint that better shows what I'm thinking about.

[Thomas Vaught]

Quote:

"You mention the plate being about half the width of the bench. What is the front to back [depth] aprox. dimension?
Does the deflector plate run the full depth of the flow bench? If so then the airflow path would be from two directions toward the flow orifice. The air would hit the deflector and move left or right, bend down and approach the flow orifice from two directions.

In order to minimize turbulence, I was leaning toward the air coming from the discharge hole then moving forward toward the front of the bench, passing down into the flow orifice plenum through the long narrow rectangular opening I described in the previous post and then flow back toward the flow disk opening from a single direction."



The Superflow deflector plate would mount about where you show your orifice opening going horizontal to the front wall of the bench.

The super flow orifice would be on the lower angled section of the
bench.

Quote:

"I'm picturing the flow to be smoother coming from a single direction than it would be coming from two or perhaps 4 directions as it flows over a deflector plate. The number of directions being related to if the deflector plate runs the full front to back dimension of the plenium. What are your thoughts on this?"

According to Harold Betties, the Super Flow tech expert, the SF benches are designed to work with turbulence as there is always
some turbulence in a typical bench. The deflector is there to make
sure they have some turbulence, not the opposite.

Food for thought.

The bench is also a ratiometric bench and just compares the flow of the test part to the orifice flow. Once it is calibrated the ratio will
easily be expressed on the inclined manometer.

You will most likely get "tumbling" with your design which is a form of turbulence and it may work great.

Tom V.

[JRM]

Ok now I really want to redo the flow bench. So what mods would you guys do starting form the flow plate on up. What does everyone think would be a good hole size for the plate. Heres what I'v got to work with.
running 8 vacc motors from grainger (can't rhember the brand but they susposedly flow 105 cfm each according to the counter sales guy)
Virt manometer the goes to 35"
incline manometer that is graded from 0 to 100 %
both dywer (sp) brand.
A copy of the MSD bench.
Performance Trends black box
2 Alum plates with 4" hole in each (sharp cut edges)
And a hole lot of insanity (LOL)

[larrycavan]

I'm uploading an updated sketch to better show my thoughts. I would purchase and add a flow straightener. I've seen them posted on here with the supplier info.

For hole sizes, I read an old post from a guy in Australia. I like what he's chosen. I've pasted them below with his comment.
-begin paste-
0.750" - 38.1 CFM
1.054" - 75.3 CFM
1.490" - 150.5 CFM
2.107" - 301.0 CFM
2.581" - 451.6 CFM
2.980" - 602.1 CFM
3.332" - 752.7 CFM
3.650" - 903.2 CFM

I machined the plate from 3mm (0.120") aluminium plate and now I am wondering if the thickness of the plate will affect the flow through it. The orifices are bored straight through and have no chamfer or radius on either side.
-end paste-

Now, note this. My superflow 110 calibration plate flows about 4% more on intake than exhaust according to their 110 manual. As I recall, the plate is sharp on one side and slightly radiused on the other. I'll check today and get back to you. In any event, even if you make your own calibration plate. Have it flowed in both directions to verify what you actually have. I'll post the correction factors as well.

If you haven't already done this, do yourself a favor and connect both of your manometers together. I expect your Dwyer inclined is calibrated for 6" unless you bought something custom from them. Whatever the case, if you connect them together and perform the following calculations, you'll be assured you have the inclined manometer mounted properly.

Let's say you have a 6" rise for the inclined manometer. Check your mounting as follows.

.5x.5x6=1.5
When you see 1.5" on the verticle manometer, your inclined manometer should be reading 50%. Use the same calculation and check it at .25, .5, .7 and 100. Obviously at 100 you should be reading 6" on the verticle. I would do this check with one of your lower flow ranges. Doing this will allow you to head into calibratiing with confidence. Being as how you purchased Dwyer manometers I would expect your's will all match up nicely. My home made inclined was off a couple percent even when mounted properly and the measurments for the inclined are dead nuts on according to calculation figures. I expect there is some variance in my 5/8" well that may be influencing the readings. Mine was off by 1% at 50% and 1.5% at 60 and 70% then up to 2% at 100. Also I built my inclined to rise in the well like a superflow does rather than drop like the MSD design. I'm using distilled water and the Dwyer green wetting agent for now. I'll be switching to their violet 1.0sg fluid as soon as it arrives at my local granger store. It's a little expensive but it won't freeze on me.


I'm also going to make a little manifold that allows me to switch from intake to exhaust without disconnecting and reconnecting the inclined manometer leads.

I would just like to add that information I found on this forum has been very valuable to me. It made me regain my interest in the flowbench again. What was once frustrating has now become crystal clear through the sharing of knowledge on here. Thank You to everyone that posts on here.

[Mouse]

Larry,
Something you may want to consider is that if your measurement orifice is not in a symetrical orientation to your fixture opening, you may very well have different readings if you do not place your test piece in the exact same position with each test session. If that is the case, a proper calibration is not possible since your calibration will depend on where your calibration piece is placed on the fixture opening.

Keep in mind that a proper bench will have good balance, which will give you readings within 1% where ever the calibration or test piece is placed on the fixture except for the very edge of the fixture for sharp edge calibration orifices. A calibration tube should not be effected greater than 1% when brought to the very edge.

John

[larrycavan]

John,

The odd thing is that the calibration plate is located in the exact same position each time. The top of my bench is covered with a piece of 1/4" aluminum plate. I drilled and tapped the mount holes for my fixture. I used the Superflow calibratin plate for the template when I located the holes so everything is centered with regard to the 4" hole in the top of the bench.


Since the calibration plate is symetrically located each time, what would you attribute the slight difference in readings between the verticel and inclined manometers when they are connected together?

Also I checked and the Supeflow calibration plate flows more on exhaust than on intake. One side of the large hole is slightly radiused and the other size is sharp edged. I don't know why they designed it that way. The manual indicates that it should flow more on exhaust as well. Superflow gives a 4% spread of the flow range as acceptable and you simply use a correction factor to indicate the actual flow range as compared to the test plate.


Larry

[JRM]

On the superflow 600 bench What are the size of the holes in the seperator plate? or are they just using 1 hole.

[Mouse]

Larry,

I am a Pitot tube person so I am sort of trespassing onto the orifice side of the forum and do not know a lot about orifice flow systems, but I have gained quite a lot of knowledge about orifice flow characteristics from making calibration orifices for calibrating and testing Pitot tube flow systems.

In my opinion, it is suitable to place the calibration orifice in the center for calibrating purposes. But if you don't have a locating system for the cal plate, like you do, and the flow readings will vary with the location of the cal plate, then there may be a calibration issue. And since cylinder head valves are usually located to the very edge of a fixture, a good balance is needed for valid readings. A side note: A more suitable tool for checking balance in intake and exhaust mode, and for "dead spots" is a section of tubing inserted into a plate.

I am not sure why you are getting different readings on your manometers but I am also not sure I understand the situation or question.

You say "one side of the large hole" and also "the other size of the hole". I am not sure if you are referring to two different calibration orifices. But assuming you are referring to a single cal orifice with a sharp edge on one side and a radiuse on the other, this is a typical sharp edged orifice. There has been very good discussion on this forum about sharp edge orifices that you may want to find and review. But in breif, a sharp edge orifice is a very reliable way to meter air flow since the sharp edge eliminates a lot of flow rate variables, so flow rates are easy to calculate under ideal conditions. The radius on one side is needed when using thicker materials to form the sharp edge. You want the sharp edge to always be the leading edge of flow. Now, the reason why you will get higher flow rates in the exhaust direction leads back to my "ideal conditions" comment. When the orifice is measuring in the intake mode, the air entering the orifice is the ideal condition with no initial velocity and no bounderies nearby to effect the flow from all directions 360 degrees. But in the exhuast mode, (again the sharp edge being the leading edge of flow), the air entering the orifice will have some initial velocity, be bounded by the fixture walls or the fixture opening, and have some level of turbulence from the plenum or settling chamber. These are not ideal contions and the result using a fixture while calibrating results in a higher rate of flow through the orifice.

JRM, If you are asking me, I don't know, sorry.

John

[Thomas Vaught]

Mouse,

He is not swapping the orifice around so the sharp edge is always
facing the direction of flow, therefore one side will flow differently
than the other due to the different discharge co-efficient.

The Super Flow bench has the same issues but they calibrate around them.

The Intake flow ranges on a Super Flow 600 are APPROXIMATELY:

Range #1 = 37 cfm
Range #2 = 75 cfm
Range #3 = 150 cfm
Range #4 = 300 cfm
Range #5 = 450 cfm
Range #6 = 600 cfm.

These flow ranges are based on a using 6 inch delta P manometer
(Dewyer) Model # 246 but with "Blue" 1.92 specific gravity manometer fluid.

Hope this helps.

Tom V.