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bnam
Samba Member
Joined: July 02, 2006
Posts: 3553
Location: El Dorado Hills CA/ Bangalore, India
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 Posted: Wed Apr 29, 2009 3:55 am Post subject: FI shroud -- venturi ring not a venturi ring |
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I remembered reading about the added ring in FI shroud as a means of providing additional cooling. But, after reading more about it today, it seems to me that it is being mis-named as a "venturi" or "velocity" ring.
Venturi effect does increase velocity, but it decreases pressure -- and the velocity decrease once it passes the venturi so by the time the air hits the fan it will be at the same speed as before. So, the intent of the ring is not to increase velocity of the airflow IMO. The velocity at the fan and more importantly thru the cooler will be the same as before.
However, if the flow were more efficient (laminar) it would be possible for the same fan set up to deliver more airflow thru the heat exchanger. So, IMO it's purpose is more likely to be to improve laminar flow.
Anyway, is there any actual data on whether it works?
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volkaholic1
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Joined: October 31, 2004
Posts: 894
Location: ohio
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| Posted: Thu Apr 30, 2009 7:53 am Post subject: |
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The quick answer - Does it work? Yes. Remember VW added this ring originally to provide more cooling for the late model FI engines.
Proof? - Besides just sayings "because VW did it", the only hard numbers I have is that I have seen significant oil & cylinder head temperature reduction when running the ring. Also, you can hear a difference in the fan, OK, I know that is weak, but it is true. The engine just sounds different. I have no actual air flow velocity data. I do not have the equipment to conduct such tests.
The physics - The ring inner edge physically sets down inside the fan. This draws the air farther down into the fan before it can be flug outward by the fan. It really is more like a velocity stack on a carb in that respect, helping straighten out the air for more laminar flow. But since the diameter necks down, then expands back out, it is like a venturi. I have no hard data, but it should create a lower pressure zone at the narrowest point. Should it be called a venturi ring, a velocity ring, or something else? I have never seen any actual VW literature on the subject. What do they call it?
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Bruce
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Joined: May 16, 2003
Posts: 17694
Location: Left coast, Canada
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| Posted: Thu Apr 30, 2009 7:56 pm Post subject: Re: FI shroud -- venturi ring not a venturi ring |
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| bnam wrote: |
Anyway, is there any actual data on whether it works?
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I believe Jake saw a 10ยบ reduction across the board in head temps.
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TallCity
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Joined: January 12, 2008
Posts: 570
Location: Bust'n my knuckles
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| Posted: Thu Apr 30, 2009 8:04 pm Post subject: |
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I found a non-doghouse fan shroud that had one of those v-rings on it. It looks factory with factory looking spot welds. Wonder where it came from?
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Money does not buy you COMMON SENSE but it does buy you a better COFFIN.
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rtroy
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Joined: June 03, 2009
Posts: 260
Location: California
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| Posted: Sun Aug 22, 2010 2:10 pm Post subject: Re: FI shroud -- venturi ring not a venturi ring |
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| bnam wrote: |
I remembered reading about the added ring in FI shroud as a means of providing additional cooling. But, after reading more about it today, it seems to me that it is being mis-named as a "venturi" or "velocity" ring.
...snip...
B |
You are quite correct, it's a volute.
Note, however, that the one being offered for VWs today is deficient in design because it presumes that the air is coming directly in from the front of the engine, but it isn't: The air is coming in radially toward the fan center. A proper solution would curve more in recognition that the opposite side of the volute is the firewall itself.
Also note that the stale air thermostat serves this purpose, too, and is nearly as good as the Porsche volutes they used on some of their engines, in part because the "throttle ring" inducts air between the throttle ring and the shroud in addition to induction between the throttle ring and the firewall.
...That they work is easily demonstrable and sufficiently well documented - you can take it to the bank, though any particular volute may not work as well as another - all are likely better than the stock setup on fresh air systems.
Regards,
Richard
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Richard
Karmann Ghia and Porsche 356 enthusiast
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