From: Gary Casey [glcasey@gte.net]
Sent: Wednesday, November 01, 2000 10:11 AM
To: 928
Subject: [928] Re: turbo charging vs supercharging

I have done engine management systems for both crank-driven and
turbine-driven superchargers and just to use up bandwidth and clog the
internet, here are my opinions on the subject:

1.  The supercharger is more bulky than the turbo and is likely to be more
difficult to package.
2.  The supercharger is mechanically more complex with the belt drive,
alignment, etc., but the turbo is much more complex plumbing-wise.  It needs
at least 6 plumbing connections and as many as 10 (turbine in, turbine out,
waste-gate out, compressor in, compressor out, boost signal to waste-gate,
oil in, oil out, coolant in, coolant out).
3.  The OEM's dropped turbo's primarily for emission reasons - the catalyst
is harder to warm up with the extra mass of the turbo in front.
4.  The turbo is more easily adjustable for boost level.
5.  A positive displacement supercharger can build boost at lower rpm than
typical turbo installations, but a turbo is more likely to have low end
boost than a centrifugal supercharger.
6.  For a given boost level the turbo is easier on the engine as the power
to drive the device is taken before it gets to the crankshaft in the form of
back pressure.
7.  The turbocharger takes out about half the power loss with altitude and
becomes more efficient as the altitude goes up.
8.  The turbo is lighter in weight for most installations.
9.  Durability for the turbo is much better than for either of the others.
10.  With the extra exhaust plumbing the turbo adds more heat to the engine
compartment.
11.  The turbo is much more sensitive to the installation and the exact
match of the turbo to the engine.
12.  No way to completely eliminate the turbo lag - although I drove a
Subaru rally car that was totally awesome.

just my opinion...