Well, this is really proof that a good engine has the application in mind. A 90 deg V gives the best dynamics, in that it is perfectly balanced 1st order and usually not bad 2nd order (V8-not balanced, V6-unbalanced in rocking, V12-perfect).

Trouble is the thing may not package in a modern FWD car. Anything smaller than 90 deg just allows the thing to occupy less space, while still allowing the "V6" badge on the back. Lots of work goes on to get the best dynamic compromise possible - a straight 4 could be seen as a 0 deg V!

A good engine is a marketable engine...

Mart

As far as I've read, the VW "W" engines are solely based on the VR6, which was developed as a compromise between a "real V6" and an inline 4 or 6.  I say "real V6" because the VR6 has a very shallow 15 deg offset between cylinder banks, and the cylinders are staggered, allowing both banks to share the same cylinder head.  All this was done simply to save space, which is how they managed to shove a V6 into somewhat tiny engine compartments.  Throughout the years, the VR6 has proven itself as a very reliable and modifiable mill.

After VW and Audi became the same company, the VWs started getting bigger to fall in line with the larger luxury Audis.  A bigger chassis gives you a bigger engine compartment (in most cases) so they started spooning "real V6s" into their larger models (Passat, A6).  Now that they're building even bigger cars (Phaeton, A8) and have all kinds of room, why not slap two proven VR6s together?  Actually the W8 came first, which essentially chopped the last two cylinders off of 2 VR6s, and later decided to leave 'em there and make a 12 cylinder.  Plus now they have the bragging rights to say they have a 12 cyl.

However, I do doubt that they'll make a W10, since that would have each cylinder bank set up in a "three-and-two" arrangement, introducing more balancing headaches for very little gain.  

This is all a very long way of saying GraviMan's right, it's mostly just packaging details.

A very simplified VW engine layout:

VR6:         W8:         W12:

O O O       O O          O O O
 O O O       O O          O O O
                ----         ------
                O O          O O O
                 O O          O O O

Aorangi,

After some clicking I found the really cool VW engine page, it's sort-of "dumbed down" but you may find it interesting.

http://www.vw.com/engine/flash.htm

Hi guys,
It looks like I've somewhat badly formulated my question. It wasn't especially related to the VW W engines. These must be considered as conventional V engines but a made of two VR engines on the same crankshaft. The VR 6 and VR5, (now called simply V5 and V6 since they have the new heads with 4 valves per cylinder) are not real V engines, but rather in line ones with cylinders offset in a 15° angle in view to shorten their overall length. This is evident if one consider their respectively 6 (for the V5) and 7 (V6) main journal crankshafts.

That's why the angle of 72° between the banks of the W8 and W12 would be ideal for a W10 in view to get even firing intervals with two rods on the same journal, and since the V5 is in production, a W10 could be made. But instead, VW produce W8 and W 12 which have their rod journals offset respectively by 18° and 12°! By the way, these rod (as well as main) journals are so narrow due to the very short crankshaft that it is chilling. But this is not the subject I intended to raise in this thread.

I understand that in Formula 1 engines, the V10 are set at other angles than the ideal 72° (for even firing intervals with 2 rods on the same crank) for packaging, center of gravity height and aerodynamic reasons. But please don't tell me that a 65° angle for a V12 such as the Ferrari ones has packaging advantage over a 60° one and that the 90° V10 of the Dodge Viper and the VW V10 TDI have also packaging advantage over a 72° V10  ! (Note that this V10 TDI has nothing in common with the spark ignition ones W8 and W12.)

Graviman, with two rods on a single crank journal, a 90° angle provides even firing interval for a V8. For a V6, you get it with a 120° angle, for a V12 with a 60° angle, for a V10 with a 72° angle.  

Cheers,
Aorangi