hmm, well, it seems both of you ethier didn't understad what I wrote, or chose to argue different points.
CV6MTX, your arguments for efficiency hinge on improperly sized units for the twin turbo setup. and as such your argument is entirely based on a particular application with particular hardware. My argument was that a twin turbo can have benefits but which one was better completely depended on the application, its intended use, and the particular hardware being considered.
I have never argued that a single is not a good choice in many many situations, just that more often than the 5-10% you guys seem to claim is the twin (or more) turbo setup optimal. Heck, I even stated that for my Contour I would go w/ a single.
I still don't understand how you can believe that a twin turbo must inherently run at a higher pressue to make the same airflow as a single turbo. This is preposterous. For a particular application, if you design both a single setup and a twin setup intended for the same peak hp, each of the smaller turbos should flow half (or slightly more) of the cfm designed for the larger single turbo and at the same pressure. Again, it comes down to choosing the right turbo, both the compressor trim and the A/R ratio for a given application for which one is more efficient, and if both setups aren't pretty close for compressor efficiency, you have sized them incorrectly.
As to the VATN turbo, the durability info you have is honestly almost irrelevent, because you have no idea the actual failure rate vs. the amount in service. Your experience, while definately worthwhile, doesn't mean much in that particular argument. Now, a warranty claims summary for VATN turbos and a close estimate of how many are in the field, that could be useful in determining how reliable they are.
As to easier and cheaper. Cheaper, yeah probably because the VATN turbos are a bit more expensive than a good T3, but easier? I dunno, because the VATNs I know about don't require external oiling or cooling. plumb the intake and exhaust, throw a boost reference line to it and it all good, no need even for a real wastegate. Packaging is much easier too because it doesn't require an oil drain, so it can sit lower if you want, and it has more flexibility as to what angle it is mounted at, heck they claim you can even mount them vertically.
Bigprobe,
wtf does a little extra heat matter from the hot side of the turbo? as long as you don't have things sensitive to heat unshielded or too close to the turbo extra heat is irrelevant, and it isn't even extra heat, its 2 smaller areas of roughly the same amount of heat in different spots, sometimes this even makes things more manageable than a single. ok wait I'm confused, then you jump right back into compressor efficiency???? sure a smaller fan is going to have to spin faster to get the same volume of air as a larger fan, but remember you now have TWO fans to make that larger amount, so the smaller fan only has to make HALF what the larger fan does (am I the only one that grasps this concept?)
as to the Boost threshold comments, I was merely correcting your improper use of the term lag, for the non-turbo savvy that may be listening. I was not implying a search on my part for a particular boost response.
As to added complexity in adding a second turbo, yes it is there, but it is not always as difficult as you make out (sure a sequential would be, even in intake plumbing alone!) In a V-type (or flat) engine, exhaust plumbing is often much simpler for a twin turbo than a single (crossover tubes and all that) and it is typically much easier to place the turbos closer to the exhaust ports than a single. Intake plumbing may be a bit harder to do for a twin, but, IMHO intake plumbing is much easier to fabricate than exhaust plumbing.
Sure a 2nd oil line and water line will be needed (for some turbos) but since you are already doing one, a second usually isn't that big of a deal, and in some cases you can even tee off the first line (if they are large enough)
