I would bet my FOOT Sway is right though in his description... I dont,,, but professional engineers think about and work like this... I bet it's right.

 

I would have thought that if you started with a good example you could flock a fibre glass copy readily, which would at least assist the air flow issues caused when they are missing. Adding CF would improve the rigidity.
jp 83 Euro S AT 57k

 

What's the deal with the front S4 Belly pan?
Everyone seems to sell a really nice aluminum version, but the ducts are not included?
I like where it says "remove your ducts from the old one"-
(If I had an old one to remove them from)
Were the ducts a separate part #?
What are they actually cooling?
They look like they have a specific purpose.
Is anyone still fabbing them?
I have been told the factory front pan is still available-but no ducts-

 

PC-85 - You might want to start a new thread since the question applies to 87+ only.

For 87+ cars it is said not to install an undertray without ducts because the heat will slowly fry the motor mounts.

The much better aftermarket aluminum undertray does not come with ducts. The new factory part did when I last checked. So if your budget allowed you'd buy that, bash the heck out of it for a while until it's worn out, remove the ducts, and put them in the new aluminum undertray. On my aluminum one I transferred my one remaining duct combined with a used duct I bought from a 928 shop. It was pricey but a fraction of the cost of a new flimsy factory undertray.

 

Well I got chewed out in track inspection for not having one. Even thought it is useless IMO they were still complaining.