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  #11  
Old 04-08-2020, 11:30 AM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,574
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Quote:
Originally Posted by Bavafa View Post
Can you please elaborate on this and what is it involved in getting the data?

Thinking out loud, I would think that a good set of data would be driven by first having it flying with the stock size, 2.5" and then enlarge it to the FM150 size of 3" and then get the performance data.

I am also wondering if the shape of it will make much of difference, although we are only enlarging it by .5"

Am I off the mark on this?
Mehrdad,

The idea would be to send samples to Don Rivera at Air Flow Performance and have him test them on the flow bench. He would measure the pressure drop across various snorkel configurations.

The shape of the transition between the 2.5" and 3" bores certainly matters a lot. Nothing worse than an aft-facing step -- that is, having the tube abruptly expand from 2.5" to 3" diameter going downstream with a square step.

Ideally, go farther upstream in the snorkel where the diameter is bigger, and make a smooth transition without any restriction/reduced diameter. Second best is to gently expand out from the smaller diameter to the 3" diameter over as much length as you can.

The need for the gentle transition is that you are making a diffuser that is slowing the flow down from the higher velocity in the smaller diameter section, and you want to effectively slow it down with no flow separation to get the full available pressure increase. What happens with the aft-facing step is that the flow separates and you just have a jet of the higher velocity going into the larger diameter tube. The jet breaks down through turbulence so that you end up with the slower velocity, but no pressure increase. The available pressure increase was wasted in viscous dissipation.

At the same time, I would love to have Don test with and without the filter, and with the filter with a small radius lip around the perimeter to help the flow turn over the corners and down into the filter.
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Last edited by scsmith : 04-08-2020 at 11:37 AM.
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  #12  
Old 04-29-2020, 09:08 AM
Raven31 Raven31 is offline
 
Join Date: May 2009
Location: Sumter SC
Posts: 34
Default I have 2 snorkels

I have 2 snorkels and live in SC .. willing to send one in for test. I?m faced with the same issue anyway with A FM-150. Just learned about this on Saturday.

Rob
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  #13  
Old 04-29-2020, 09:24 AM
Stockmanreef Stockmanreef is offline
 
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Location: Midland, mi
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sent you a PM
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  #14  
Old 05-18-2020, 08:24 PM
Raven31 Raven31 is offline
 
Join Date: May 2009
Location: Sumter SC
Posts: 34
Default Results

Got the results back from Don today.

I sent him an unmodified stock snorkel.

“An airflow test was performed on the subject air duct to compare pressure loss through the duct when attached to a standard RSA-5 and FM-150 fuel control. Calculating airflow for an IO-390 the maximum rated airflow would be no more than 1400 PPH. The following charts show airflow through the respective fuel control without the duct installed and with the duct installed. Flow numbers do not account for air filter loss as this part was not supplied. Carb loss numbers are in inches of water. Airflow numbers are for air at standard sea level air.

WIDE OPEN THROTTLE FLOW TEST WITHOUT AIR DUCT INSTALLED

Airflow PPH - 600 - 800 - 1000 - 1200 - 1400
RSA-5. 1.5 2.6 4.3 6.4 8.8
FM-150. 1.5 2.5 4.0 5.9 8.0

WIDE OPEN THROTTLE FLOW TEST WITH AIR DUCT INSTALLED

Airflow PPH - 600 - 800 - 1000 - 1200 - 1400
RSA-5 2.0 3.4 5.3 7.6 10.4
FM-150 1.8 2.9 4.7 6.8 9.5

Flowing the duct at 1400 PPH airflow with nothing attached to it gave a loss of 6” H2O. The duct has an opening at the flange that would attach to the inlet of the fuel control of roughly 2 5/16” diameter. The FM-150 has an opening at the inlet of the fuel control of 3” diameter. Taking the area change of 2 5/16 and opening it up to 3” without accounting for any other flow losses in the duct, the loss through the duct would go from 6” to 2.1”. Doing this on the installation using an FM-150 would more than likely eliminate the added loss from the duct. This would be the equivalent of an additional 8% airflow to the engine.”


I plan on sending a modified snorkel to Don once we get one completed for comparison.

Hope this helps the group!

Rob Arduini

Last edited by Raven31 : 05-18-2020 at 08:32 PM.
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  #15  
Old 05-18-2020, 08:30 PM
Raven31 Raven31 is offline
 
Join Date: May 2009
Location: Sumter SC
Posts: 34
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Sorry looks like the formatting got messed up once it posted. the 2 digit numbers should be under each of the PPH. Ex. 600 should have 1.5 under it, 800 should have 2.6 and so on.

Let me know if it?s not clear and I?ll try to fix it.

Rob
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  #16  
Old 05-18-2020, 09:56 PM
Bavafa Bavafa is offline
 
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Location: Sacramento, CA
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Thank you Rob for posting this, eager to see the comparison with the modified snorkel
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