From: bcasper@eos.ncsu.edu (BRIAN  CASPER)
Subject: Re: Supercharged vehicles
Originator: bcasper@c00100-100lez.eos.ncsu.edu
Reply-To: bcasper@eos.ncsu.edu
Organization: North Carolina State University
Distribution: rec.autos, rec.autos.tech, rec.autos.sport
Date: Wed, 9 Sep 1992 16:01:56 GMT


In article <1992Sep8.191953.27701@news.nd.edu>, mikeb@nowaksg.chem.nd.edu (Michael George Buening) writes:
|>In article <1992Sep8.161221.28786@athena.cs.uga.edu> dug@athena.cs.uga.edu (Douglas Brown) writes:
|>>I've been hearing some about the new "supercharged vehicles."

Superchargers were used on WWII airplane engines, so they've been around for
a long time...  That big blockish thing that you see on top of a top fuel
dragster engine is a super charger.  They are also commonly referred to as
'blowers'.  A 'roots' style blower is made of a housing with two interlocking
vanes inside.  One of these vanes is belt driven by the crankshaft.  An end
view of a vane would be like three lightbulbs joined at the bottoms to form
a three point star with bulbous points - only smaller - about 4-5 inches in
diameter.  This triangular vane is about 6 inches long (typically...  is that
what the 6 stands for in a 6-71 GMC blower???)  The two vanes interlock like
a pair of gears.  The carberator (or throttle body injector) sits on top of
the housing and the housing is bolted to the intake manifold.  Port injection
is still done near the valves.  As the blower spins, it draws the mixture
through the carb and forces it down into the plenum of the manifold.

Other types of superchargers exist.  A 'screw compressor' uses the same basic
principle as roots type, but the vanes are twisted more like a screw in an
attempt to smooth out the pressure pulses that tend to form from the eggbeater
effect of a standard vane.

And then there is the Volkswagen G-ladder compressor that was used briefly
on the Carrado.  If I'm not mistaken, this system used a fixed nautalis shaped
vane and a floating similiar vane which was driven by a small cambered wheel.
As the wheel spun, the moving nautalis would squeeze the air along its chamber
until it forced it out of the end.  Simultaneously a new puf of air was being
compressed at the beginning of the spiral.  VW's claim was that it produced a
constant stream of air without pulsation...

|>>Does anyone out there have any comments on these.  Are they good?  Are they
|>>bad?  Compared with a turbo charger?  What does everyone think?

I have always liked the idea of supercharging more than turbocharging.  Turbo's
are associated with lots of engine compartment heat and excess heat is
typically something you would want to reduce for better performance.  Since
a turbo spins at such a high RPM, it is essential that the centershaft is
properly oiled or failure is immenant.  One arguement against superchargers
is that they rob hp at low RPM due to friction, so gas mileage suffers.

|>>I know of the Ford Thunderbird SuperCoupe, Pontiac SSEI, Buick Park Avenue
|>>Ultra, and a few more are supercharged.  Are there anymore?
|>
|>I have always been under the impression that a supercharger worked
|>over a wider rpm range as opposed to the turbocharger that only
|>gives boost at higher rpm's.  I too would like more info on these
|>systems so I'll keep an I out for this thread.

Since a blower is crank driven, the pulley ratio can be set up to provide
boost at any desired RPM range.  Unlike a turbocharger which relies on the
rise in exhaust gas flow rate to speed it up, there is no 'lag' or time dealy
for this process to take place.

I hope this is helpful.  Corrections are welcomed if I've missed a point...
-- 
-- 
Brian Casper                |   "I like to study psychologists.  It gives
bcasper@eos.ncsu.edu        |    good insight into what rats are thinking."
  Pinball Consultant        |     -  Dr. Oscar Wesler