Cayenne vs Touareg

[Tom Leppke-Hennig]

This thread has reminded me of a question I have always had, but never
been able to find a clear answer on: What is the inter-relationship of
all the different V8s in the VAG/Porsche family?

These are the ones I am wondering about:

Porsche V8 #1: Used in the 928, various displacements and head
configurations, but always the same foundation.

Audi V8 #1: V8-V8. Unrelated to the Porsche, as far as I can tell by
comparing bore, stroke, basic block design etc.

Porsche V8 #2: Cayenne. Related to Porsche #1 or Audi #1 or #2? I don't know.

Audi V8 #2: Used in A8, A6 4.2, Tooregg. Related to Audi #1? I don't know.

Does anybody have the straight dope on this? Does anybody else care?

Generally, developing a whole new engine architecture is expensive, so
companies borrow heavily from existing architectures like The I-4, or the 
I-5, or the 924 I-4, which is where I think the 928 V8 came from.

Ti?

Tom LH
1995 90 with suspiciously VW 2.0l X-flow 8V looking cylinder-heads.