"Costas Charalambous" <ckc822@yahoo<img src=/i/dc.gif border=0 width=35 height=15>> 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.