Turbo vs. Supercharger.

[nealtovsen at yahoo.com (Neal Tovsen)]

> I'm not completely
> sure exactly how it works, but from what I have been
> told there is a nozzle of sorts that is constantly
> varying how much exhaust flows into the turbo.

Sheesh! Another self-proclaimed forced induction
zealot who has not read his Corky Bell books! Man, you
guys need to get with it! <grin>

http://www.aerocharger.com/

They sound like they'd be really cool. Mr. Bell
recommends these very highly. But from what I've
heard, they're quite expensive. I have no experience
with them outside of the Bell books...never seen one.
They either must be REALLY expensive, or there is some
disadvantage that no one is mentioning. Or maybe their
marketing department just plain sucks!

I have a few comments, with regard to altitude
adaptability: The "turbocharger vs. supercharger"
debate really isn't as such. It's really a matter of
the manner in which they typically control their
maximum boost levels, NOT the designs of the
compressors themselves. Turbos use a wastegate (or
similar) based on a set maximum pressure.
Superchargers usually simply calculate the maximum
boost they want (which requres picking a starting air
density), and put on the pulley that gives them the
required charger RPM.

However, turbo bearings, like those on a supercharger,
DO have a maximum RPM, and they do reduce efficiency
when you approach it. If a turbo is set to achieve the
maximum boost possible within it's efficiency range
and within the redline RPM of the bearings at sea
level, then it will exceed these parameters at a
higher altitude. In the best case, you take a
significant hit on efficiency. In the worst case, you
wreck your turbo! The wastegate wouldn't know the
difference, or care. Eric's big "turbo advantage" only
works when the turbo is operating well within design
parameters at sea level, with enough headroom to spin
faster at higher altitudes without blowing up or
running off the efficiency charts. So a production car
does receive this advantage, but modified turbo cars
running higher-than-stock boost should be very careful
at altitude!

A variable-diameter supercharger pulley that could
vary RPM independant of engine speed would not be
terribly difficult to design. This would compensate
for various altitudes, just like a turbo, and could be
built to guarantee that you wouldn't exceed the
maximum RPM of the charger. However, the advantages to
a production car probably aren't enough to warrant the
additional cost/complexity, and a race car team would
find it much easier to simply change pulleys when they
race at altitude.

Neal

__________________________________
Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!
http://sbc.yahoo.com