RMk,
I think I understand what you are getting at, and I will offer my educated opinion on the matter.
First, I would like to clarify that Audi's "biturbo" setup isn't any different in concept than a common twin turbo setup for a V-type engine. The less common ones are the sequential setups, like those found in the turbocharged versions of the 3rd gen RX-7 and the last Supra. Sequential setups are good, and offer much better low-end boost response at the expense of high complexity, and the smaller turbo ends up choking things off a bit at higher rpm. Sequential setups are rarely, if ever, found in aftermarket installations.
In other words, this statement, is backward.
The thing with the Noble is that it's another "traditional" style twin-turbo setup, in that it uses one turbo to spool up the other. It's not exactly the same thing.
The Noble does use a traditional style twin turbo, and so does the Audi, the one you describe for the Noble is actually a sequential setup, and is rarely used, but most notably as a stated above.
The Duratec 2.5 (and 3.0 for that matter) are in a unique situation, where the airflow requirements of the engine are such that a properly sized single turbo will work almost exactly the same as a properly sized twin turbo setup. This, coupled with the fact that there just plain isn't any room for a turbo on the rear cylinder bank (the engine and exhaust manifold back right up to the "firewall"), leads folks to the decision to use a single turbo.
No doubt that the Audi is a very good example of a well engineered OEM turbo setup, but the Audi design is considerably affected by several factors that are completely different from the contour situation. One major one is that the audi engine is mounted longitudinally, and not transverse like the contour, this gives them room to mount a turbo on each side of the engine. They also use two small intercoolers to make better use of the package space, while still providing adequate intercooling capacity, and not compromising the engine radiator's efficiency.
While on the subject of intercoolers, I must say that I do not recommend a turbo setup without proper intercooling. There is just no excuse for it. It invites dangerous detonation needlessly to skip doing a proper intercooler, especially on a higher CR application like the duratec. Mr. Hightower and his cohorts at street flight, realize this, and have addressed the issue w/ a nice water to air intercooler design (though the prototype is fugly, lol). Further, I think that most supercharged applications should be intercooled as well, even the vortech for the contour. Mr. Rowe made a band-aid attempt at covering this on his s/c'ed SVT by using a water/alcohol injection system (a band-aid solution at best, and Mr. Rowe fully realizes this) and met with some success, though he has been plagued by other problems.
I would also raise some doubt on your blanket statement that a twin turbo setup is always the best way for "max boost" even if only applied to the CSVT. There are many factors involved, not least of which being package issues, that drive the selection of a single turbo.
Other factors being things like cost, turbo availability (ie proper sizing for the application) complexity, and the minimal (if any) difference in performance between a good twin, and a good single.
Also, if I had a turbo car that took up to SIX SECONDS to make boost (like you state above) I would get rid of that setup as quickly as I could, or even the entire car.
Oh, and may I recommend the book "Maximum Boost" by Corky Bell as a very good basic turbo book, that is heavily geared toward practical knowledge, and won't bend your brain around stuff that even engineers would have a hard time with.
Fwiw, I am in the process of putting together a minimal cost twin turbo setup for my 94 Mustang Cobra (still hunting for the proper turbos at a reasonable price). I also have some experience in the area of automotive engineering, as well as many, many friends, far more knowledgeable than I, that I pull information from on a regular basis on subjects like this.
I love technical discussions
), getting the biggest bang-for-your-PSI. Whether or not a setup like this will fit under the hood of a CSVT remains to be seen. This entire thread is purely speculative, like many posts I've started (I have quite the imagination :rolleyes: ) and I started it to query the group as to what they knew about TCs... but that's not what I got back, to my surprise.