What the heck is a W12? I understand 12 cylinders but a W shape and configuration?? Think of 2 compact V6s smashed together. Volkswagen did it with their top-of-the-line Phaeton luxury sedan, as well as for a new super-car concept they were coming up with. Which would make great cars the only problem being they had a VW badge. Same thing with the Phaeton ....it is a great sedan, but it is hard to plop down enough money to buy a 7-series or an S-class on something with a VW badge. The ironic thing is that VW owns Bentley, Porsche and Audi, and that VW by itself is a really serious and very competent manufacturer.
Anyways, a W-12 is basically 2 compact V6s put together. Maybe Spktyr can give a better answer (hint hint Ping for you Spktyr LOL).
Here is a pic of the VW supercar concept.
Would be a great car to compete with with Ferrari 430 and the Lamborghini Gallardo (and even the Murcielago). But again note the badge issue. It might be prudent for them to consider badging it differently ....maybe as an 'uber' Audi (VW also owns Audi)to avoid some of the issues they got with the Phaeton. Oh, and the upcoming Audi A8L with have a W12 if certain things work out.
Hm, guess I'm on deck. Ever consider running an automotive ping list, spetz?
To understand the W12, you have to go back a little bit in engine history. For the purposes of this discussion, we're going to assume that all these engines will be used in a longitudinal or "north-south" configuration where the crankshaft is aligned with the car's long axis.
Traditionally, there have been two successful form factors for reciprocating piston engines used in cars; first, there is the inline, where all of the cylinders are aligned in a row or line. So called "straight sixes" and "straight eights" as well as the common four cylinder commuter car engine are of this format. (A special case of the inline engine is the "slant-six", where an inline six is tilted onto its side a number of degrees in order to make it take up less room vertically. More on this later.) The other type is the "Vee" type where the cylinder bank is split into two banks placed at angles to each other, creating the angle between them that gives the form factor it's name.
Most V-type engines have a 45, 60, 90, or 180 (called a "flat" or "boxer" engine) degree separation between the two cylinder banks. In other words, the angle between theoretical lines drawn straight down the piston connecting rods on each bank would be a certain number of degrees. The most popular and most successful V6's of late have been 60 degree V6s, where each cylinder is offset 30 degrees from vertical. As a comparison for you dinosaurs still dealing with inefficient creaky old American V8s, the vast majority of those are 90 degree V8s - where the cylinders are at right angles to each other.
Why a V-configuration engine, you may ask? Well, if you make the cylinders short enough, you can interleave the cylinders in such a way that you can have a V8 engine that has a short overall length, on par with an inline four. You can also get a low hoodline by using a high angle V engine - it takes up less space vertically. However, by doing so, you make a number of trades - you reduce the number of main bearings you have in the engine (an inline eight has nine main bearings, a V8 has four) which increases the stress on the remaining bearings, a vee engine produces more stress than an inline does on bearings because unless it's a "boxer" vee you never have balanced power pulses, and you now have a very wide engine which may not fit in a smaller car. You will also have a vibration issue because of the uneven power pulses that needs to be dampened somehow, and you'll have a lot of wasted space under the arms of the vee that you can't put things in (unless you want to annoy your customers and mechanics by installing accessories that can't be serviced from the top).
An inline six or eight is stronger and will live far longer than a vee-type of the same size and number of cylinder, but is much longer and taller; this leads to their own packaging problems. You can lay an inline down at an angle on its side (the "slant" engines to reduce the hoodline, but again that means that you have to make the car wider to accomodate the engine. However, the smoothest running engines in the world are inlines or siamesed inline engines with an even number of cylinders greater than four (V12s, V16s).
So, if you're looking at a six cylinder car from a design standpoint, you *want* to have an inline six, but you may not be able to deal with the packaging issue. The corporate 60 degree V6 looks awfully tempting, but you'll have to shoehorn it into the engine bay because it is so wide, leading to servicing issues. (Look at a 300ZX or 350Z's engine bay for an example - the engine is shoehorned in between the strut towers, and there's minimal room.) So what to do? Most makers just accept that the engine bay is going to be short on room if they're going to meet today's styling, efficiency, and other packaging constraints. VW did something different.
Continued in the next post.