turbo/supercharging

[Robert Harris]

Not flames - just 2 cents.

The positive displacement mechanical supercharger aka GMC Roots is the most
maligned, mythed about and lied about good thing ever.  For sheer
simplicity and overall good power, it is very hard to beat.

To start with, since it is positive displacement, there is very little
backflow - no matter what.  Set the blower speed ratio and thats the size
of the engine.  When air goes in, the only way out is the exhaust.  Dial
your ratio and thats your displacement. VE smee E,
don't matter - the simple manifold is emminately adequate as the air is
only going one way - in.

Next, carbing it, fueling it whatever - simple piece of cake.  Pick a unit
for a Naturally Aspirated engine of the same size as your blower is working
at.  Bolt on - it will be very close - no boost curves, no major
compensations needed.  No trick shit, no magic. but don't let that stop you
for going for the final 5 per percent that tricking it can bring you.

The power curve much more closely approximates the curve of a naturally
aspirated engine of larger size than most turbos.  Cams - shorter duration,
higher lift intakes - better for low end work fine - whatever is pumped
goes into engine - much less dependent on cross flow and VE than turbo. 
Thus you can run a torquer cam and still make explosive top end power.

The supposed in-efficiency compared to a turbo is there - but how
significant is it?  Disconnect the belt and drive home at 80 anyway, the
airflow will turn the rotors freely - but yes, it does take power to run. 
Cleaning up the exhaust can regain some of the loss.

V8's love them - also, ask the Supercharged Ford T-bird V6ers what they
think.  Very simple install.  If clearance a problem a Tee on top can route
to sidedraft webers or TBI type injection.

Passing the fuel thru the blower results in finely mixing the mixture by
mechanical carboration and lowers the charge temp significantly - partially
compensating for no intercooler.

For those engines that it can be bolted on, it is hard to beat for the
street and other racing.  Turbos can be taken to extremes that are beyond
the roots, but they are an order of magnitude more tricky, expensive and
complicated than the old fashioned roots and depending on what you want,
not offer that much more.  Read all the posts about tweaking and peaking
turbo stuff - reminds me of trying to get a carb tuned properly.

And then, there are the truly possessed - green pea soup and all - who have
been known to twin turbo a blown V-8 to reach numbers that make no reality
whatsoever.

Either way, positive pressure makes much more power and thats all that
counts.

If the first ingredient ain't Habanero, then the rest don't matter.
Robert Harris <bob at bobthecomputerguy.com>