Posted for "George Braly" <gwbraly@gami.com>:

 I have provided engineering support for one such effort and I have done the
number crunch in relation to another.
 
 There are a  LOT of issues,  besides the noted large amount of Hp that is
siphoned off of the crank shaft to provide the boost.
 
 Regards,  George
 

"""
  Of late I have heard a lot of pros and cons to the idea of adding a
  supercharger to my IO550 (non-pressurized) Lancair IV.  Some startling
  information (right or wrong) tells me that the supercharger consumes as
  much as 50 - 70 HP for the belt driven unit.  Clearly, if that is true,
  it would require a significant boost from the supercharger just to get
  back to where I start out horsepower wise.  The purpose of this message
  is to get at the facts.  I would sincerely appreciate any and all posts
  that might shed light on this issue.  The more information, the better,
  especially if there is anyone reading this that has one, has had one, or
  is considering one.
 
  Berni P Breen
"""