Turbo vs. Supercharger.

[drew at scirocco.cs.uoguelph.ca (Drew MacPherson)]

In the world of variable geometry turbines the VNT is the current cat's
ass (or hot ticket, for those that don't hang around with me enough...)

The VNT uses nozzle vanes to direct exhaust onto the turbine rotor.  The
term "nozzle" refers to the portion of the turbo that directs the 
exhaust gas onto the turbine.  All turbos have a nozzle.  In the case of 
the VNT, the variable vanes allow a varying nozzle effect - ie the gas can 
be directed onto the outer portion of the turbine for fast spool up with 
low gas velocity, and onto the inner portion of the turbine for high 
airflow and boost regulation.

It's common to see VNT described as variable vane turbo AND/OR variable 
nozzle turbo.  Tomato/tomatoe says I.  The variable vanes result in a 
variable nozzle effect.  As I understand it there is no difference between 
the two - they describe the same sort of VGT.

Drew

On Wed, 2 Jul 2003, Neal Tovsen wrote:

> 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
> > 
> > -- 
> > /=============================================\
> > |  84 Wolfsburg Edition TurboDiesel Scirocco  |
> > |    http://scirocco.cs.uoguelph.ca/gtd       |
> > \=============================================/
> > 
> > 
> > _______________________________________________
> > Scirocco-l mailing list
> > Scirocco-l@scirocco.org
> > http://neubayern.net/mailman/listinfo/scirocco-l
> 
> 
> __________________________________
> Do you Yahoo!?
> SBC Yahoo! DSL - Now only $29.95 per month!
> http://sbc.yahoo.com
> 
> _______________________________________________
> Scirocco-l mailing list
> Scirocco-l@scirocco.org
> http://neubayern.net/mailman/listinfo/scirocco-l
> 

-- 
/=============================================\
|  84 Wolfsburg Edition TurboDiesel Scirocco  |
|    http://scirocco.cs.uoguelph.ca/gtd       |
\=============================================/