Non A*E* Roots Numbers

[Greg Hermann]

>>One of the more significant things to observe in the numbers posted here is
>>how LOW the VE for a Roots is at low engine/blower speed--these low VE
>>numbers at low speed translate to not much boost there until the revs are
>>up a bit!! A VATN turbo will actually get the boost up a LOT SOONER than a
>>Roots or a Screw huffer!! Get it up rates for VATN turbo/
>>Roots/conventional turbo are prolly sorta comparable to the same rates for
>>a 15 year old boy/ 30 year old man/50 year old man!
>>
>>Another point to consider--Don't even THINK about running a Roots or a
>>screw in "blow thru" configuration!
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>I agree completely with your comments regarding the "Roots" blowers.   On
>the other hand, "Screw" compressor technology has come a long way over the
>years.  You might be surprised by the performance figures for an optimized
>screw unit, no matter whether you want to examine  1)Dry Discharge
>Temperature   2)Adiabatic Efficiency   3)Volumetric Efficiency   4)Parasitic
>Power   5)Internal Compression Ratio...........etc.  Sized correctly,  a
>screw(s) can nearly match the peak efficiency of a good turbo system, but do
>so over a much broader range, with near instant response (wet or dry).

I have looked over the VE/AE curves for the various Autorotor screw units
provided by Whipple, among others. They are certainly WAY better than what
a Roots will do, but the VE is somewhat low (below 50%) until the units
rotational speed begins to pick up.Bottom line: in the real world, you will
only get near your intended boost level with one of these over about a 2.0
: 1 engine rpm range if it is properly selected and pulleyed.

A VATN turbo will get you your design boost over more like a 3 : 1 maybe
3.5 : 1 engine rpm range! Plus--it will give you FAR better cruising
economy, and it is way easier to intercool and mount. Some of them are ball
bearing, and independent of the engine's oiling system, as well.
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>Do you have a URL for the VATN turbos?

Try a web search on the word <Aerocharger>

Regards, Greg
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>Walt.