Miata Mailing List: November 1993, Message #36
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   From: capek@peach.rtsg.mot.com (Tom Capek @708-342-5639)
Subject: clutching superchargers
   Date: Wed, 3 Nov 1993 09:41:36 -0500

The concept of clutching a supercharger is only possible if you have the
proper type.  The Roots-type, or positive displacement design (I think), can
not be clutched since no air is delivered to the engine if the supercharger
does not revolve.  This is the type you see on fuel dragsters that started
out as superchargers for diesel trucks.  The design usually consists of two
long interlocking lobed "gears" that trap air between the lobes and pump it
into the engine.  The one plus of this design, lots of boost.  Dragster
typically lose 300-400 horsepower to spin theirs, but get 1000+ as a result.

The vane-type supercharger is just like a fan blowing into the engine.  There
is clearance between the blades and the housing so that air can bypass easily.
These are the types being used on some of the GM cars.  Pluses of this design,
include less heating of intake air, less horsepower to drive, but less boost.
These usually have to be overdriven, ratio wise, to any produce noticeable 
boost (i.e., spun faster than engine rpm).

My question is, why would you want to clutch it?  I don't think that you are
going to get your stock mileage back during cruise conditions (low boost) due
to the added intake restrictions.  AND, you fallen into the same trap as
with turbocharging, lag time.  If you think that the engine rpm dances when
the A/C clutch cycles, what about a supercharger?  Smooth application of
throttle would be impossible.  A little bit of throttle, then BLAM, 50 more
horses.  I wouldn't want that in fifth gear on a crowded freeway.

just my thoughts

tom capek