Aerochargers are better than a twin screw!! hahaha ;-)

[Greg Hermann]

At 8:31 PM 10/14/01, Stephen Andersen wrote:
>The boost curve for the Positive Displacement SC
>on aerocharger's web site is about as far from a
>"fact" as you can get.  When sized and "geared"
>properly for a give displacement engine, a PD
>supercharger will provide within about 10-15% of
>peak boost given WOT at somewhere just off idle.
>
>The twin screw compressors have extremely high
>volumetric efficiencies and don't need to be spinning
>very fast to generate boost.
>
>Aerocharger's site indicates that the boost curve
>is linear and starts at or near zero.  Way off base...
>
>Steve
>
>Stephen M. Andersen, P.E.                              (302) 326-6405
>Technical Director                                    FAX  (302) 326-6401
>AdvanTek International, LLC                     Cell   (302) 547-9842
>56 Read's Way                               andersen at Advan-Tek.com
>New Castle, DE 19720

Steve--

I respectfully suggest you get a copy of the VE and AE curves FROM WHIPPLE
for the various Lysholm compressors which they sell, and run some numbers
on what level of boost you will get on a given engine at a given
engine/compressor rpm --without exceeding the compressor mfgr's suggested
maximum compressor rpm at the motor's redline rpm. (If you know how to do
this.)

(I am assuming that you are NOT talking about running a variable speed
compressor drive.)

I went through this VERY exercise in an effort to find a way to put forced
induction onto a 60 cid, 1800 rpm tractor engine. It was all VERY
enlightening, believe me !!

The fact is that the Lysholm type screw compressors need to have some
rotational speed before their VE rises to anything approaching a reasonable
level. Further, their VE does NOT go that impressively high, even at its
peak.  (It is ONLY impressively high if one is comparing it to a Roots
blower !!)  And, furthermore, while the Lysholms have a decent AE, it is
NOT the equal of what can be achieved with a well designed and selected
centrifugal compressor wheel and housing.

AND, furthermore, with all due respect, I  suggest that  you might want to
consider omitting the part of your signature which is in excess of just
"Steve" when making technical comments that appear to be doing little more
than regurgitating the content of a magazine article ! After all, there
_ARE_ certain "professional responsibilities" that go along with stating
your professional title ! :-)

Greg (also a P.E.)


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