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Info: Positive displacement vs. centrifugal superchargers

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Re: [VW-VR6] Eaton Supercharger "Paul, Greg" <greg.paul@tallan> Wed, 18 Apr 2001 14:28:54 -0400
[gti-vr6] Re: [VW-VR6] Eaton Supercharger Ian Frechette <frechett@rintintin.Colorado> Wed, 18 Apr 2001 15:24:07 -0600
Re: [gti-vr6] Anyone removed the suitcase? Ian Frechette <frechett@rintintin.colorado> Thu, 16 Aug 2001 13:59:21 -0600

From sentto-360611-3245-987618554-aqn=panix@returns.onelist Wed Apr 18 14:29:20 2001
From: "Paul, Greg" <greg.paul@tallan>
To: VW-VR6@yahoogroups
Subject: Re: [VW-VR6] Eaton Supercharger
Date: Wed, 18 Apr 2001 14:28:54 -0400
to me, this is why i'm interested in an eaton unit.

Stomp the throttle, and the
valve slams shut...hang on for the instant power. NO LAG. High boost levels
are found at low rpms (due to the design of a positive-displacement Roots
type blower like the Eaton). Centrifugal blowers compress the air charge
using inertia. As the impeller spins, it flings air particles outward due
to centrifugal force. This increases the density as rpms increase.  Result?
Max boost at max rpms, but....boost is in direct proportion to rpms.


anyone care to contradict this?  anyone running a rimmer system?  their
webpage doesn't seem very useful.

----- Original Message -----
From: &#97;qn&#64;panix<img src=/i/dc.gif border=0 width=35 height=15> &lt;mailto:&gt;
To: &#86;W-VR6&#64;yahoogroups<img src=/i/dc.gif border=0 width=35 height=15> &lt;mailto:&gt;
Sent: Wednesday, April 18, 2001 2:10 PM
Subject: RE: [VW-VR6] Eaton Supercharger

"Costas Charalambous" &lt; &#99;kc822&#64;yahoo<img src=/i/dc.gif border=0 width=35 height=15> &lt;mailto:&gt; &gt; wrote:
> I havent' seen anything about an Eaton Charger kit for the VR6 in a couple
> of years.  the one on the NewDimensions site is the Neuspeed unit for the
> 2.0 4 cyl engine.
> ND was developing a VR6 Eaton or a Rimmer kit (I can't remember which,
> perhaps Holland can tell us), but it looks like they scrapped that idea. I
> think they installed one on their old VR6 Passat wagon. But I don't think
> the Eaton chargers are as efficient as the centrifugal type
> least that's what I got out of the European Car article a month ago.

  More info on that here:

  (For access, use id: driver   password: hired )

Andy Nguyen \ &#97;qn&#64;panix<img src=/i/dc.gif border=0 width=35 height=15> \

From sentto-1455644-1661-987629050-aqn=panix@returns.onelist Wed Apr 18 17:24:13 2001
From: Ian Frechette <frechett@rintintin.Colorado>
To: gti-vr6b@yahoogroups
Subject: [gti-vr6] Re: [VW-VR6] Eaton Supercharger
Date: Wed, 18 Apr 2001 15:24:07 -0600

"Costas Charalambous" &lt;&#99;kc822&#64;yahoo<img src=/i/dc.gif border=0 width=35 height=15>&gt; wrote:
>But I don't think
>the Eaton chargers are as efficient as the centrifugal type
>least that's what I got out of the European Car article a month ago.

Yes and no.  The Eaton and Rimmer positive displacement units all
generally have a bypass or clutch mechanism that allows them basically to
run with no load (a couple hp to turn it) until you romp on the gas, then
they engage and away you go.
Once they're under load though, they drag on the engine a lot more but they
also push more air in at low rpms for instant response, and build pressure
linearly with higher rpms.   Some of them have a problem flow at high rpms
though, so they tend to fall off powerwise.

Centrifugal compressors like the Z-eng and Vortech units are naturally
more efficent.  They have very little load at low rpms, and generally have
greater flow capacity at higher rpms given a particular size blower, but
their pressure actually goes up more along the lines of the *square* of
the rpms.   As the EC article mentioned, if you rev em too high the boost
and power can become uncontrollable (they cited a 1.6L engine revving
to over 8k rpms, and it made an additional 50hp with each of the last two
thousand rpms).   It also means that the resistance on the belts increases
exponentially with rpms so you only go so high and then start slipping.
That and their power below a certain rpm is pretty tame.  Even with all
that the boost feels like it comes on pretty smoothly, and at least
it's always in the same place unlike a turbo which spools up partially
depending on engine load and throttle position instead of rpms.

One big problem with the screw type positive displacement units
is that they're typically quite long physically.   They're often
mounted on top of the engine, or in a transverse layout in front of it, or
behind it.  The VR6 engine compartment really doesn't lend itself to any
of these placements, and the blowers are too long to fit in the same
space that you can put a compact centrifugal blower where
the stock airbox was.


From: Ian Frechette <frechett@rintintin.colorado>
To: list@gti-vr6
Subject: Re: [gti-vr6] Anyone removed the suitcase?
Date: Thu, 16 Aug 2001 13:59:21 -0600
"Costas Charalambous" &lt;&#99;kc822&#64;yahoo<img src=/i/dc.gif border=0 width=35 height=15>&gt; wrote:
>Is the Eaton supercharger a positive displacement unit?  I think New
>dimensions squeezed one in there a couple of years back, but never
>produced a kit because of software issues.

Software issues weren't the only problem from what I heard.  Sounded
to me like "Neuspeed issues".

Anyway, yes that's a Roots type positive displacement type blower.
Neuspeed stuck it back near the exhaust manifold and ran a long belt to it.
It pushes the same volume of air with each turn, at any rev so
the power increase is linear.  They're typically overdriven so they
make boost off idle, and usually include an air bypass or clutch which
effectively takes the supercharger out of the loop when the
intake manifold is running in vacuum (idle, low speed, part throttle).
At full throttle the blower kicks in and away you go, even right
from idle.  They make the engine feel bigger.  A 4 feels like a 6.. a 6
feels like an 8 and so forth.  They tend to run out of steam at higher
rpms though because the positive displacement compressor is flow limited.

A centrifugal supercharger like the Vortech unit or Z-eng uses
a centifugal compressor wheel like a turbo charger, but larger and
spun at much slower rpms.  It makes no boost at idle, and often doesn't
really come on till after 3500-4000k rpms (the Vortech does make some
boost as low as 2k rpms).  On the upside, the boost increases exponetially
with rpms and they can move a lot of air so they aren't usually flow
limited.   It feels like the engine starts out stock and gets bigger as
you go faster.  It often seems like the speedometer is going up faster
than the rpms.

Turbos just feel.. well.. turbocharged.  Stock off idle, then at
some magic rpm the hand of god reaches down and gives the car a big
shove like you're a tiny car sitting on a Hotwheels track.  What's odd is
that the experience is very much the same whether it's a chipped 1.8T,
a blown VR6, or my dad's Dodge 4500 lb Dodge with a Cummings
Turbo Diesel making 505ft-lbs of torque.   Nothing.. then BIG SHOVE,
and at high rpms it falls off again.   It's just a question of
ultimate velocity in each gear with each shove.


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