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Date: Wed, 15 Jun 2005 09:26:21 -0400 (Eastern Daylight Time)
Subject: Superchargers - was Failure to compute
From: "Ian Dewhirst" <idewhirst@dewhirst.ca>
To: flyrotary@lancaironline.net
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Dave Staten wrote:

"Obviously nothing is free, but from a net standpoint, the turbo is more
energy efficient than is a mechanical drive supercharger."

Hi Dave, I was not comparing the two, but since you brought it up...  I
think that you will find that the Lysholm type supercharger renders the
"turbocharger is more efficient" argument obsolete.  Typically these
compressors have peak adiabatic efficiency at or above centrifugal
designs.  I am not advocating one type over the other,  In my experience
the choice has more to do with ease of integration then efficiency.  Both
work if done properly.

We both agree that it takes energy to compress air, it is easy to see that
a belt driven supercharger will consume some of the power that is being
produced by the eShaft.  On the other hand putting a turbine in the
exhaust path produces back pressure, back pressure reduces VE.  The amount
of power you will be able to generate at the flywheel is directly related
to VE.  VE is, after all, what we are trying to improve with a
“super”charger, mechanical or exhaust driven.  We are only able to improve
VE because we are driving a more efficient air pump (hopefully) then the
engine is by itself.  This is not always that easy to achieve given the
operating range of an automobile engine.  To illustrate my point: The TII
utilized a 66% increase in manifold pressure to generate a 20% improvement
at the eShaft.  The REW utilizes a 78% increase in manifold pressure to
generate a 64% improvement at the eShaft.

The TII is good example of engineering done by the Mazda marketing
department, the REW is a good example of the engineering department
figuring out how to keep marketing happy and still make some horsepower.

Don’t get me started on automotive journalists and the perceived value of
making full boost just off idle…

Cheers -- Ian