Its a cool air duct. Some of the alternators have them, some don't. It looks like the 5ktq had one, but doesn't now. The CQ never had one, and I can't remember if the 5kq has/had one.

Its probably not needed, kinda like the blower for the injectors on the CIS turbo cars.

This is definately for cooling..why some have it and others don't don't ask..
but it runs down to durability issues...your altenator gets hot that's for sure especially if you have heavy loads on it (altenator)..and then add engine temps to it..it causes wear and break down faster.
Especailly on the bearings..now it could be that certain models have them just because of the power options (IE...power seats & bose)...

on the newer Audi's to get durability issues way down they have started to switch to water cooling the genearators...you can see one of these on the new VW Phaeton & new A8,,,and then A6...

PF

Not so sure that is not needed. Remember the system is an antique as far as FI goes. Datsun Z's had the same Bosch system on their turbo cars. They also had the cooling fan. The manual explained that it was a retrofit/cure because of something similar to "vapor lock".

Yes I realize that, but I've seen a few 10vt's in typ89's w/out the cooling system. Also, if you have seen/feel it work, well, its not a very good system IMO. It was moving more hot air around than anything else when I checked it yesterday on the 5ktq after a drive. Also, hardly any air was felt at the injectors, only a good amount coming out of the rectangular hole on top of the shroud/duct. And yes, the ducting is all in good (new) condition, was replaced by the previous owner.

In my recent but short junk yard trip I see that even an aluminum back plate was used on some Audi alternators in the place of the light colored plastic one most frequently found. Interesting to note that mine when I replaced it last week had obvious signs of heat burn on the plastic. This leads me to think then, with that turbocharger heat generator sitting next to it, the alternator will probably get much more life with the cover and air scoop on there so I even coated mine with more tinfoil to reflect heat.
I don't see the necessity of the air scoop on non-turbo models to prevent over heating but there is a disclaimer I read from manufacturers concerning wet weather use and moisture getting in the alternator as positioned on the Audi 5000. This is certainly open for discussion.
I got mine rebuilt last week for $28.00 but the labor is a pain in the butt. I left mine original with the cover and hose! As for the injector cooling fan, mine hasn't run for a year but the car works just fine.

Audi actually moved the alternator on the 20v cars (non turbo). The early CQ's have stainless headers which generate a LOT of heat because of their relatively thin walls (we even got sodium filled exhaust valves like the turbo cars). Anyway, the alternator and AC compressor are flip-flopped on a CQ compared to a 5k, and even a 10v 90. Don't know why Audi didn't do something like that with the turbo cars, not like there is a space issue.

Throw one of those sodium filled valves in a pond.

Hell yeah, they could have mounted it on top dead center and had Tom Faust design a mellow hood air scoop. That would look pretty cool with the other mods shown on the pics just posted. I have been wondering what fifties style mods would look like on my 5000. Lake pipes, hood, flames, skirts and a modern fin. Wish I had a computer program to do that to check the looks. Probably start a whole new thing.

I'd have to cut them open first...Magnesium can be a fun metal to play with too, assuming you have some acid (not the paper) laying around.

If you feel adventureous, can always make your own soap with NaOH and your own body fat. Just watch how concentrated you get the NaOH.

It is needed it sends cold air to the alternator to help keep it cool. It works like the blower for the injectors but there's no fan.