> What about the recent discussion regarding the longevity and complexity
of the VNT turbos? Based on that, it seemed almost as if they were more
trouble than they're worth?
Actually, the VN Turbo is less complex than a standard one. Since it is self
sustaining, you don't need all the fancy controls. Just keep the oil flow
going through it and intercool the critter. That's about the limit of the
maintenance it needs.
> Oh, BTW, Shaun, could you elaborate on the "balancing headaches" you
referred to regarding twin turbos? I assume you mean keeping both turbos
at the same boost levels? If so, what makes it difficult, and why is it
desireable to have them both exactly the same? (Even if one is at 6psi
and another at 7psi, they both route to the TB, so wouldn't they average?)
Could a single wastegate be used for two turbos? Or is this more a
function of different exhaust properties from each bank of cylinders?
(Wow, I'm incredibly annoying!) ;-) Many thanks in advance, and three
cheers for anyone who has actually bothered to read this far! :-)
Since turbos are "freewheeling", (they don't have direct power placed to them
like a blower) they can achieve strange imbalances when put together in a
"twin" or "quad" or whatever setup. The problem is where the turbos meet.
Lets say you do have one turbo putting out 6psi and the other at 7. They
wouldn't "average". What would happen is that the air wouldn't combine at
equal rates. This could cause odd vortices (especially if you combined the
air at the throttle body). The other thing is that you can cause backpressure
on the lower psi turbo. The theory is that this happens when the engine can
no longer handle all the air of the turbos and a back pressure wave goes and
actually slows down both turbos, but the lower pressure turbo will get a
bigger pressure wave, further taking it out of balance with the other turbo so
if you ram on the gas again, it comes up to pressure (speed) much slower.
This is a "worst case" senario and it happens very rarely. I don't think
they've had those problems since the early days of the twin turbos.
The problem is eliminated by making the headers "mirror" images so that the
tube lengths are the same. Also, combining the pressurized air prior to the
intercooler creates a smoother stream of air going into the TB. Post-Turbo, I
think the y-pipe and exhaust can be of any configuration, it's just the
pre-turbo that matters. Like I said, the VN turbo eliminate most of these
problems being able to self adjust. As far as I know, VN turbos only come in
one size also: Large. There's no sense in a small VN Turbo. I'd rather have
a single VN Turbo than two medium or small ones. Less plumbing, less hassles
(thus my comment about balancing).
Shaun H.
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