Cooling fan, hole cover

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Larry Coreth
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Re: Cooling fan, hole cover

#16 Post by Larry Coreth »

CJ,
So this screaming sound which appears to be emanating from your wife is this a result of your having been a naughty boy ?
:D :wink:
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David Baugh
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Re: Cooling fan, hole cover

#17 Post by David Baugh »

Larry, one needs to have experienced the politics of the automotive industry, in order to appreciate how often the marketing division over-rules the engineers. It may be price point, or an objectionable noise that cancels an otherwise beneficial system. Personally, I'll live with the noise, in order to achieve better generator cooling. Any back-flow theory is nonsense. If the ducting can't handle the volume, the fan simply won't generate it. In that case, recycling the excess might be a good thing. But, I'm confident that the engineers didn't make a mistake like that.

Maybe y'all oughta try spinning one to see what happens. I have.

Dave
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Larry Coreth
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Re: Cooling fan, hole cover

#18 Post by Larry Coreth »

David,
One does not need to have been in the automotive industry to experience or understand the economics of engineering or product cost accounting. All businesses are the same in that regard. Having been an engineer in several different industries over the past 40 years I can safely say without boasting that I understand economic compromise.

However cutting holes in the fan to cool the generator and then spending extra money to put a cover over it does not sound in keeping with low cost to me !

Dismissing the fact the cover divides the inner fan area (low pressure) from the fan housing (higher pressuure) area as non- sense would appear somewhat hubris. That the factory put the cover there is certainly proof enough that they thought it was not non-sense. That you have had no problems without the cover only proves how robust the original design was.
BTW I did a “search” on your previous posts on this subject and read them ad nauseam.
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Matthew Devereux
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Re: Cooling fan, hole cover

#19 Post by Matthew Devereux »

Balance holes (as I call them) helps equalize the pressure on the fan reducing axial thrust. The only thing the plate might do is channel air from the outside as not to disturb air flow to the generator. Whether this set-up works or not I don't know. Just my theory.
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David Baugh
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Re: Cooling fan, hole cover

#20 Post by David Baugh »

Larry, you missed the part about the objectionable noise. Cost factor was simply another example.

Wow! Talk about hubris?

Dave
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Larry Coreth
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Re: Cooling fan, hole cover

#21 Post by Larry Coreth »

I usually avoid second guessing the Porsche engineers, of the 356 era, unless I have data to support my theory or where today's technology has clearly obsoleted the original design. Both of these are rare situations foe a street driven car.

Besides there is a certain simple enjoyment to be derived from driving and maintaining a 50 year old auto. Even my 23 year old son who's only driven modern computer controlled, power everything, with performance capability far beyond what is usable on the street loves the directness and mechanical feel of the 356.
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Jim Liberty
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Re: Cooling fan, hole cover

#22 Post by Jim Liberty »

I drive my cars across the So. Cal deserts, and have never had an overheating problem. As Larry Coreth stated earlier, the Porsche engineers put it there for a reason. When ever I deviate from their engineering, I usually screw something up.

.....................................................................Jim.
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Re: Cooling fan, hole cover

#23 Post by Ivan Fuller »

The fan housing and I assume the fan are from the VW parts bin.

The very early VW fans even had fins on the afore mentioned holes - I guess to assist cooling the generator. The most extensive testing ever carried out at that time was done during the development of the prototype beetles to prove reliability so I am sure the holes were there for a reason

Anyway time moved on the fins disappeared but the holes remained.

Some engineers at Porsche decided to make an engine that would rev 4500 - 6000 rpm and discovered the VW fan made an unholy noise.

This would never have been a problem for the VW engineers (Porsche) as its unlikely the motors went much over 4000rpm.

I would suggest the expedient solution was to cover up the holes and continue using the VW part.
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Ashley Page
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Re: Cooling fan, hole cover

#24 Post by Ashley Page »

Considering how many cars VW sold vs Porsche it could be that continuing to source the fan from VW and having the hole cover made was less expensive than producing a new fan.

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Matthew Devereux
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Re: Cooling fan, hole cover

#25 Post by Matthew Devereux »

I'm told the '69 912 fan didn't have holes and was the same as the VW fan'71 and newer. I just bought a welded fin version and it seems to fit. The fan is wider too. I hope it works :)
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Larry Coreth
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Re: Cooling fan, hole cover

#26 Post by Larry Coreth »

Matthew,

Per PET the '69 912 used cover plate P/N 616.106.327.00 as opposed to O/N 546.06.204 previously used. The change came about with the change from the 350W generator to the 420W generator.
The fan changed too but obviously had holes also, thus the need for the cover plate.
VW made a wider fan (37mm) that it appears has no holes, It fits ’71 and later Bugs. Too late for the 912
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Lars Nielsen
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Re: Cooling fan, hole cover

#27 Post by Lars Nielsen »

I am not questioning why Porsche designed a hole cover, my car simply did not have one , anymore.
My main concern is if the sound I have is really from turbulence/resonance in the fan, I which case I would be surprised that people running without the cover can do so without really noticing any difference. That sound is ear piercing loud!

Anyhow, once I get my cover plate I will know.

Another thing to consider in the 356 vs. VW fan design is the pulley ratios. I believe they a different between the two and any stall/noise/cooling issue would be driven by final fan rpms.
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Larry Coreth
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Re: Cooling fan, hole cover

#28 Post by Larry Coreth »

Lars,

Why are you concerned about pulley ratios between the VW and Porsche designs ? Or is this strictly an academic question? Yes the rations are different but any problems related to the difference the Porsche guys addressed 60 years ago. In seeking a solution to a 365 problem and to assume Porsche's original design is at fault is generally futile. Only if you try to exceed the design envelope (like racing) will you experience trouble. This not to say the Porsche engineers were or their designs were perfect but they were pretty good. Plus they honed the design for 15 years and got most of the bugs out.
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Matt Kreeve
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Re: Cooling fan, hole cover

#29 Post by Matt Kreeve »

^^thanks - that's helpful ... also trying to track down the siren / whistle sound that arrives about 3.2k rpm .. am running the 26 (not orig 18 blade) fan
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Re: Cooling fan, hole cover

#30 Post by Alfred Knittel »

Do we know when the fan hole covers were first in stall in Porsche motors. We're they on pre a motors or just later ones
1954 coup
1959 Cab
1959 super coup
1970 240z first year
1971 240z

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