More interesting Results

[Chad Speier]

I had a chance to evaluate a World Products 235cc SBC head. They post both SF600 and SF1020 data on their site. I originally flowed it with a 30º backcut valve and then found out the advertised numbers were without, so I reflowed them without.

First test, their SF1020 results vs my PTS bench..

.200 128/133
.300 188/189
.400 235/248
.500 270/272
.600 281/280
.700 285/287
.800 286/291

Second test, their SF600 vs my SF600

.200 135/132
.300 198/190
.400 247/239
.500 284/273
.600 296/278
.700 300/279
.800 301/282

My SF600 vs PTS

.200 132/133
.300 190/190
.400 239/248
.500 273/272
.600 278/280
.700 279/287
.800 282/291

4.155 fixture, not sure what they used.
Brezenski plate, not sure what they used.

[blaktopr]

Chad. Which inlet radius did you use in these tests? The aluminum one or clay? I wonder what some companies use.

[Chad Speier]

Chad. Which inlet radius did you use in these tests? The aluminum one or clay? I wonder what some companies use.

I used my aluminum plate.

[larrycavan]

Good for them for posting results on both benches. Customers would no doubt prefer their SF600 flowed units. Most CFM/$$$

Give it some time and you'll see guys arguing about CFD models not being in agreement...

They actually have some specific data on flow testing on their site http://www.worldcastings.com/product_im ... ile-33.pdf

http://www.worldcastings.com/product_im ... le-227.pdf

[larrycavan]

Been thinking about this on and off for a few days now. Focusing only on the digital benches for the moment. To lend praise or fault on either bench is not the intent of this post. To say one reading is correct and the other incorrect is not the intent either.

As with all devices that measure changing results, there can and often will be tolerances of the components used in constructing the device that will affect the end result of the measurements. In the case of the digital meter flow benches, the sensors are a key player. Obviously this speaks nothing of cabinet design influence which can also affect the end results.

What's caught my eye is the non linearity of the flow number variance. We have close, then drift, the close, then drift again.... The answer, I feel, is related to sensor linearity. This link provides insight on the subject.

http://www.sensorland.com/HowPage026.html

[Tony]

Larry, there are so many possible sources of slight error and non linearity that can creep in, it becomes very difficult to separate and quantify each potential source.

But if you had the resources, you could try connecting up two (or more) completely independent digital manometers to the same bench via the air pressure sensing lines.
That should give some indication if these variations are coming from the bench itself, or the pressure measurement electronics.

My gut intuition tells me it will probably turn out to be an odd mix of both...

[larrycavan]

Tony,

Do sensors have a sweet spot?...

Would be interesting to see what happens when an analog manometer is hooked up in parallel with the digital unit on a 1020....

I sent that posted flow information to another guy that ports heads. His comment was " I'd use the 600 numbers for bragging rights" .... imagine that

[1960FL]

Larry,

Yes they do and i just lost a whole 1 page post on this Arg, i am working on a calibration mapping that looks to be following the linearity of the sensors we use, long and short of it is that with the correct internal plate size the calibration plates will line with the calculated CD Bruce uses of .62 +/_ .003. My initial tests showed that all the calibration stayed under the curve and 100, 200, and 300 CFM plates checked against a 200CFM calibration on a 430 internal, all were .1+/- CFM from there actual Measures and calculated CFM at 28 with a .62 CD. This was against the same calibration that was done with a much larger internal plate (660 vs 430) that in the end required a .608 CD and my numbers were 1++ low at 100 and 1++ high at 300.

I am working on making more plates and will be mapping at test pressures in 5" increments from 5" to 30" if i can Cal plates will be 50CFM to 300CFM in 50cfm increments. The goal is to do this with two or three internal plates using a rough 50% total internal flow as the calibration point, I/W 200 on a 400 internal.

Thoughts?

Rick

[Tony]

Tony,

Do sensors have a sweet spot?...

Would be interesting to see what happens when an analog manometer is hooked up in parallel with the digital unit on a 1020....

I really don't know the answer to that Larry, you guys are really pushing the limits....

But I will theorise that the biggest sources of initial (straight out of the box) error will be the zero pressure point, and full scale calibration point. The sensor is internally corrected for temperature, and we ourselves can ensure the dc supply voltage to the sensor remains absolutely constant.

After zero and full scale pressures have been tweaked in software, what is left will be some non linearity and hysteresis due to the mechanics of the strain gauge part of the sensor.
We can ignore hysteresis, because the random pressure fluctuations occur evenly in both directions, and after some really brutal averaging, what we are left with will be a simple very slight curvature away from true linearity.

This will be made worse because we are exploiting all of the full maximum possible pressure swing to minimise the effects of other possible errors.

Not certain about the cause of this non linearity, but my guess would be that a cross section of the measurement diaphragm acts something like a beam in bending mode, and the strain gauge part measures the tension/compression changes along top and bottom of the flexing diaphragm.

It is all geometry related, and providing the actual mechanical flexing is kept very small, the linearity should be quite reasonable.
But it would be easy to imagine how, if something like this were made of rubber, how blowing it up into a massive dome shape could introduce some dramatic non linearity into how far the rubber stretched versus the applied pressure.

If you can detect and quantify this non linearity, correcting for it should be possible, and I would expect the correction to remain fairly valid from sensor to sensor, or at least it should get you very close.

This is all armchair speculation on my part, but it is what I would be looking for.

Fluid manometers will be very difficult to read to the required degree of accuracy because of the meniscus effect, surface tension, and how the fluid clings to the wall of the tube.

It may be easier to generate an accurate static pressure rather than trying to read or compare existing pressures by different means of measurement, each of which also have their own set of problems.

How about a header tank full of water and a hose leading down into the pressure transducer.
The header tank could be raised on a lead screw to increase the static pressure by known fixed amounts without any significant fluid movement if the surface area of the reservoir were kept relatively large. It may with care and repetition, be possible to plot this non linearity and then do something about it in software.

Again all just crazy wild thinking on my part.

[1960FL]

How about a header tank full of water and a hose leading down into the pressure transducer.
The header tank could be raised on a lead screw to increase the static pressure by known fixed amounts without any significant fluid movement if the surface area of the reservoir were kept relatively large. It may with care and repetition, be possible to plot this non linearity and then do something about it in software.

Tony,
This is not at all crazy a cheep set of those 24" or 18" import digital calipers and some 12/20 all-thread a little craftsmanship and i could plot the accuracy of the 16" DP sensor quite accurately across the entire scale. Now time to start collecting parts.

Rick