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Old 01-13-2012, 11:30 AM
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again I ask does anybody now how much cfm a stock system delivers at its most efficient rpm range

cfm is a coefficient that I can wrap my brain around.
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Old 01-13-2012, 12:44 PM
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Somewhere around 1200 cfm: http://www.offroadvw.net/tech/wes/fan.html

But it's not limited to cfm, it (cooling) has to do quite a bit with pressure generated. Read through those articles by Raby. Don't start thinking about electric fan conversions
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Old 01-13-2012, 01:59 PM
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Interesting reading, thought about adding an electric fan to continue cooling once the the motor is shut off. On a timer for another ten to 15 minutes. You and I both know that motor temp climbs after shutdown dramatically.

my thoughts are that heat plus contraction and expansion is what kills a motor. So when a motor shuts down the temp spikes then drops off.
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Old 01-13-2012, 02:03 PM
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Similar in thought to a turbo timer huh?

Might be a good idea so long as it doesn't hinder the fans operation or airflow while in use.
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Old 01-13-2012, 07:26 PM
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the one thing about us ...........all of us.........here.............is we get a kick out of reinventing the wheel or else we would drive the same cookie cutters as every other dick and jane
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Old 01-13-2012, 11:24 PM
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Quote:
Originally Posted by letterman7 View Post
Somewhere around 1200 cfm: http://www.offroadvw.net/tech/wes/fan.html

But it's not limited to cfm, it (cooling) has to do quite a bit with pressure generated. Read through those articles by Raby. Don't start thinking about electric fan conversions
i'm not but i'm not sure why it would not be possible
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Old 01-13-2012, 11:40 PM
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Because an electric fan can generate volume but not a lot of pressure. You'd need a squirrel cage fan the size of the VW unit with the appropriate ducting to produce the same cooling capacity - the fans that you'll see advertised to place over each bank of cylinders is for drag use only - where the motor only needs to be cooled at the end of the race when the car is being pulled (or driven) back to the pits at a low speed.
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Old 01-14-2012, 03:10 PM
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Quote:
Originally Posted by letterman7 View Post
Because an electric fan can generate volume but not a lot of pressure. You'd need a squirrel cage fan the size of the VW unit with the appropriate ducting to produce the same cooling capacity - the fans that you'll see advertised to place over each bank of cylinders is for drag use only - where the motor only needs to be cooled at the end of the race when the car is being pulled (or driven) back to the pits at a low speed.
again not gonna modify my stock setup but how would one measure pressure.

On my car at idle or even at higher revs it does not have that much pressure at the bottom of the cylinders I stuck my hands in the lower cavities under the cylinders it felt like a house fan on the lowest setting

i even capped the heater hoses off to see if i could create more flow didn't seem to make any diff.
Also tighten the fan belt no noticeable diff. either

in fact was really hot at the third cylinder but much air movement.

and as far as the drag car setup i have not found one to look at yet.
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Old 01-14-2012, 05:42 PM
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That's a subject best left to an aeronautical engineer. The flow to the outside of the cylinders where you're feeling it differs from the pressures generated within the fan shroud, and that all correlates to the internal veining in the shroud directing airflow. You can feel the pressure differential at the fan - put your hand just to the edge of the opening on the outside (for God's sake don't put your fingers in the inlet) and you'll feel the pressure and airflow with the engine running. It's quite the amazing piece of engineering for it's day!
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Old 01-14-2012, 06:49 PM
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it felt almost the same at the inlet as it does the exit nominal

i must have something wrong with mine that may be the ultimate cause of this premature rebuild.
i wish i had another one guage the diff or if they are the same flow
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Last edited by delbertinie; 01-14-2012 at 06:53 PM.
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