Turbo vs. Supercharger.

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

The VNT uses a smaller compressor wheel for faster spool up.  Generally, 
in a fixed nozzle configuration the nozzle will direct the gas at the 
outer portion of the turbine anyways.

In order to make the VNT perform like a small turbo, you start with a
small compressor wheel.  In order to make it perform like a larger turbo
(and to keep it from eating itself,)  you redirect the exhaust flow
towards the inside of the turbine.

The idea is that you can use a MUCH smaller compressor wheel and still 
flow enough air without having the turbo self destruct at higher gas 
volumes.  The tiny KKK03 I have on my 1.6 is good to about 15psi.  The 
similarly sized VNT15 is good to about 25PSI, which is about what the 
much larger stock trim turbo that came with my 1.6 would handle.  The 
difference is, of course, that my KKK03 spools much, much sooner than the 
stock turbo did.  The VNT 15 spools just as early as the KKK03, but hangs 
in til the end like the stock turbo.

Drew

On Wed, 2 Jul 2003, Neal Tovsen wrote:
> 
> OK...that makes sense. So why then did the essay say
> that they use such small compressor wheels? A smaller
> compressor wheel would make *any* turbo spool faster.
> 
> It would seem that for a VNT you would want to use a
> normal, or even larger than normal, compressor since
> the nozzle vanes would allow you to spin it up faster.
> I'm not understanding the logic here.
> 
> Neal
> 
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