Turbo vs. Supercharger.

[nealtovsen at yahoo.com (Neal Tovsen)]

OK, so I read the essay that Eric posted. It's clear
that VNT, or Variable NOZZLE Technology is different
than Variable VANE Technology. I *think* the
Aerocharger is a variable VANE technology. There's a
picture that suggests it but their crappy website
doesn't really say it.

I think VNT is probably much cheaper to produce than a
variable vane turbine. However, like the essay said,
it isn't very good for high-performance applications
because it relies on a very small compressor wheel.
The variable vane technology would allow for a
comparatively LARGE compressor, while using the
turbine vanes to minimize spool-up time and maximum
RPM.

In the end, if you have moderate displacement, a
properly-sized turbo, and other technologies such as
variable cam timing, it isn't an issue. Regular WRX's
have a good bit of boost lag, but the STi with an
extra half-liter of displacement and variable cam
timing, has almost NO lag. I have trouble autocrossing
most turbo cars because I've never taught my right
foot to compensate for turbo lag...but I had no
trouble with the STi.

Neal

--- Drew MacPherson <drew@scirocco.cs.uoguelph.ca>
wrote:
> On Wed, 2 Jul 2003, Eric S wrote:
> 
> > As for wastegate control, yes, I am familiar with
> turbo design.  Now
> > Larry, have you seen the latest VNT turbos?  No
> wastegate...quite
> > interesting design actually...all the TDI engines
> in the Beetles and
> > Golf/Jettas after 99.5 use a VNT-15 turbo, which
> is called a "variable
> > vane" turbo....I'm not completely sure exactly how
> it works, but from
> > what I have been told there is a nozzle of sorts
> that is constantly
> > varying how much exhaust flows into the turbo.
> 
> VNT (variable nozzle turbo) has been around for a
> while - It was actually
> available on Shelby ed.  Shadows etc. in limited
> numbers back in '89/90.  
> The nozzle position is controlled by either manifold
> pressure (simplest
> method) or an electronically (ECU) controlled vacuum
> modulator (in the
> case of the TDI.)  The nozzle position is moved from
> the outside edge of
> the impeller at low exhaust velocity or manifold
> pressure, to spool the
> impeller quickly.  As boost builds, the nozzles are
> redirected towards the
> inside of the impeller to slow the impeller (and
> regulate boost.)
> 
> The system works very well (as anyone who has driven
> a VNT TDI could tell 
> you - well, except for Cathy - I'm pretty sure hers
> has taken a vacation)  
> If I could find a reliable (!!!) method of
> regulating the nozzle, I would 
> retrofit one of these on my 1.6 TD.
> 
> > Well, I'll tell you, turbo lag on these really
> dosen't exist...the
> > VNT-15 on the TDI engine is at full boost by the
> time you hit 1700 rpm
> > or so...basically almost right off idle.
> 
> Yes, the VNT build boost very quickly - which is why
> messing with it is 
> rather dangerous... :)
> 
> Drew
> 
> -- 
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