terminology and turbo questions

[james accordino]

I'm interested in hearing responses to this thread as
well.  I wanted to post something about this when
someone wrote about underdriven pulleys to reduce
parasitic power losses.  We used to clip the vanes on
the water pump for the same reason.  It actually takes
quite a bit of power to drive the WP.  I don't know
that I'd try this on an Audi though.  I wonder what
the race teams did?  Clip the vanes or run an electic
drive to the WP?  Anyone know what they did, although
I don't know if it has any relevance to street driven
Audis.

Jim Accordino

--- auditude at neta.com wrote:
> JShadzi at aol.com wrote:
> >
> > << Also,  the psi rating of a turbo....
> >  Is this the pressure on the turbo outlet, pushing
> into
> >  the intake?>>
> >
> > Well, turbos are not rated for psi per se, but
> typically the actual
> > psi output is measured in the intake manifold
> where it counts.
> >
> > << Or, is this the pressure of exhaust acting on
> the
> >  turbo spooling fins?  >>
> >
> > No, that pressure is typically not measured, as
> what is really
> > important is in the intake manifold.
>
> Would it be a correct statement to say that
> "clipping" mods done
> to the exhaust turbine fins results in better
> performance, due to
> less backpressure of the exhaust getting out of the
> motor?  At the
> expensive of boost onset rpm (is that different from
> "boost lag",
> which is said to be different in Max Boost)?
>
> At some point, the turbo can be too small, and be a
> restriction to
> the output of the exhaust, right?
>
> I realize this is a different topic than where the
> thread was, but it's
> a factor too, isn't it?
>
> Is the backpressure created by the turbo a factor in
> its efficiency
> for a certain pressure?  I know that clipping
> changes the a/r, and
> that it makes it "act" like a larger turbo, but is
> this simply due to
> the decreased backpressure?  Or, does it have more
> to do with the
> new shape of the fins and the new angle at which the
> exhaust
> gases hit them?
>
> Thanks,
>
> Ken


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