Just a curious thing here.
My older, historic F-Vee (Elfin) has the early (1200) type fan with the lesser amount of blades and supposedly the smaller crank pulley. There are no extra holes anywhere in the fan shroud other than the throttle cable passing thru it and the cable is sleeved in that hole to a tight fit. The stock oil cooler is in there.
This thing makes the most fantastic screaming whine between 5200 and 6500 RPM. The thing simply sings not unlike a gear whine but the frequency does not change with RPM, it just gets louder.
Replaying a video taken of the car revealed the scream to be actually louder than the zorst note and this is confirmed by following drivers.
I cannot seem to locate exactly the noise whilst revving the thing up in neutral.
I dont really want to get rid of the noise :thumb but I am curious as to whether anyone has heard of this and found out why?
L8tr
E

Never heard of that before... especially as the frequency doen't change only loudness.... although at that engine speed ,the parts involved are spinning at Very High Revs and the change in revs isn't all that great at that speed.
The only thing I can thing of that can really make a noise and that would be, either the brushes in the generator or the bearings in the generator. I just looked up one of My 9 VW workshop manuals and the generator does have two ball bearing similar to a 6303ZZ or 2RS. I really don't think it would be the bearings, but it maybe the fan belt , at that high engine speed & generator speed , the fan belt will be slipping on the generator pulley... whether it makes a noise I don't know....
regards
Lee Noonan -VW enthusiast since 1962-

Talk to Boris at Vintage in Sydney 02-9789-1777, hes raced F Vees and sponsors them as well.

He will explain the fan noise to you

I'd follow Dave's lead.

But I woulda thought it was the fan belt slipping. When I was plotting fan air flow curves for the vw fans I had real trouble getting the fan belt to grip at high fan speeds (above 8,000 rpm fan speed) which is what your talking about. The only way we noticed it was fan belt slip is because we were monitoring the engine rpm and the fan rpm seperately, and could tell when and how much slip occured.

Hmmmm valid points.
I have spun up the fan sans belts and the bearings/brushes are virtually silent.
Thing is its almost like a whistling gear whine coming from, say a Hewland F/Ford 'box. The whistle is very consistent and smooth sounding, like a straight cut gear whine and thats prolly why I tend to discount it as a belt screech.

I could not get the correct length belt at one stage and i had to fit so many shims between the pulleys that the belt was almost running on the pulley half alignment lugs and it was absolutely guitar string tight and the whine/whistle came in about 200 odd revs lower. Expected with the change in drive ratio.
We run the belts completely loose, close to the point of flicking off to (hopefully)promote slippage of the fan under accellaration but this makes no difference.
Curious.
L8tr guys
E

Without hearing this sound it a little hard to know, but...

I have heard a sound similar to your description in the past and it turned out to be the fan rubbing on the housing. It only made the noise at higher revs (not as high as you are describing) and required us to move the fan housing slightly, giving the fan a little more clearance (just placing a little pressure on the top of the fan housing with my hand was enough to stop it from whining

Just a thought.....