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

[Greg Hermann]

OK--see my post to the list. For want of a better word, I think it is fair
to say that the Lysholms have a wider "dynamic range" than even a well
selected conventional turbo, and that a VATN turbo, in turn, has a wider
"dynamic range" than a Lysholm.

There is NO doubt that any type of a turbo allows getting a much higher
expansion ratio out of an engine, whereas a mechanically driven
supercharger has no effect at all on the engine's expansion ratio.
Certainly, there are very significant efficiency/bsfc implications to this
fact.

I think I gave a decent synopsis of my thoughts on the reliability problems
which have been experienced with VATN's in my post to the list, as well as
my thoughts on curing said problems.

As far as ethical boundaries go, no, I don't think you "crossed" any,
either. The other side of it is that there are a _LOT_ of guys here (on the
list) with a _LOT_ of heavy duty credentials. Most of them don't feel the
need to flaunt them. It tends to keep the discussions a bit more
egalitarian when it's done that way, and that approach _does_ seem to add
to the availability of knowlege on the list.

What I mean by "egalitarian" is--present facts, back 'em up, and let them
stand or fail on their own. No one should presume that anyone elses facts
(or writing) are rendered more credible (on the list) because of anyone's
credentials. I have found that taking this approach on the list to be good
exercise in logical thinking as well as humility !

What makes the list worthwhile to most is presentation of facts, nothing
else. I wanted --and apparently got-- your attention because I figured you
were either talking down to the list or had not really done your homework.
I'm sort of glad it was the former, because, at least you are _capable_ of
contributing more to the list --all that is needed would be for you to
decide to go ahead and DO it. Of course, if the latter were the case, that
wouldn't be possible.

There are many on the list who _don't_ know that the Lysholms are NOT quite
as efficient as a well selected centrifugal.  Lot's of folks seem to think
that because the Lysholms have been described as "much more efficient"
(than Roots blowers) that they must also be much more efficient than good
centrifugals! The numbers you quoted below would have been useful toward
the education of a lot of folks.

Later--

Greg

At 9:35 PM 10/14/01, Stephen Andersen wrote:
>Greg,
>
>I "respectfully" have copies of the Lysholm compressor maps
>in my briefcase, and have done the requisite efficiency
>calculations.  While I agree that the lysholm AE is not that
>of a centrifugal compressor, they are still pretty darn
>good (range of 58-64% for my car), compared to 30-50% for
>a new style (Eaton) Roots.
>
>My point was not really one of efficiency (although I did mention
>it), but that rotational speed of the compressor does not have to
>be very high to get high pressure output.
>
>In my application, shooting for 7.5-8 psi, I am quite confident that
>the Lysholm will give me at least 6+ psi at 1500 rpm. and climb
>from there.
>
>Since you are accusing me of just "regurgitating" magazine info,
>I would like to know on what you base your comment that aerocharger's
>little plots are "fact"?
>
>Care to share?
>
>And I'll keep the PE in my sig thanks, I don't think I have
>crossed any ethical boundaries here...
>
>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
>
>
>> -----Original Message-----
>> From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
>> Behalf Of Greg Hermann
>> Sent: Sunday, October 14, 2001 10:13 PM
>> To: diy_efi at diy-efi.org
>> Subject: RE: Aerochargers are better than a twin screw!! hahaha ;-)
>>
>>
>> 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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