Date: Thu, 29 Sep 2005 19:22:09 +1200
Reply-To: Andrew Grebneff <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Andrew Grebneff <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
Subject: Re: yet another engine choice - VW "twincharger"
In-Reply-To: <5.2.0.9.2.20050928100242.02daccf8@mail-hub.optonline.net>
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--></style><title>Re: yet another engine choice - VW
"twincharger"</title></head><body>
<blockquote type="cite" cite>Maybe in your part of the globe a
supercharger is a turbo, or a turbo is<br>
a supercharger.</blockquote>
<div><br></div>
<div>It has nothing to do with geography. You can even look it up in a
dictionary. Colloquial usage does not in any way imply
correctness.</div>
<div><br></div>
<blockquote type="cite" cite>You were thinking right Tim.<br>
Andrew wasn't.</blockquote>
<div><br></div>
<div>Not at all.</div>
<div><br></div>
<blockquote type="cite" cite>OK, I thought that Superchargers were
belt-driven (giving immediate boost), while turbochargers are
spun by the exhaust stream (hence the turbo lag).</blockquote>
<div><br></div>
<div>Nope... that's the usual misconception. a supercharger is any
mechanical device which forcefeeds air into an internal-combustion
engine. It can be driven by electric motor, gears, shaft, chain, belt,
exhaust... even in theory by hydraulics.</div>
<div><br></div>
<div>Turbos can be driven by exhaust (almost all), belt (Paxton) or
electric motor (as VW was paying Mitsubishi to research in the
90s).</div>
<div><br></div>
<div>Turbos in their early days (WW2) were called turbosuperchargers.
Unfortunately, with the contraction to turbocharger, it's "outta
sight, outta mind"... take super out and soon people forget that
it IS a supercharger.</div>
<div><br></div>
<div>Any supercharger canm be called a blower. Of course all blow.
Including turbos. What's so difficulty to understand about that?
That's what they're for.</div>
<div><br></div>
<blockquote type="cite" cite>Paxton has been bolting supercharger's on
the front of engine for years<br>
with good results.</blockquote>
<div><br></div>
<div>Supercharger's WHAT? Oh, you mean "superchargers". It's
a plural. NEVER apostrophize a plural... unless you intend to show
that it's a possessive. The Paxton is a turbo. Take a look at one.
It's just driven by a belt.</div>
<div><br></div>
<blockquote type="cite" cite>By technical specifications a Turbo
Charger is a special type of<br>
supercharger. Supercharger is a generic term, where turbocharger is
a<br>
specific term.<br>
<br>
Often (outside of engineering circles) the lay public refers
to</blockquote>
<div>superchargers, as those which are only belt driven, which is
incorrect.</div>
<div><br></div>
<div>Exactly!!</div>
<div><br></div>
<blockquote type="cite" cite>You just can't overdrive the
supercharger's beyond the engine's</blockquote>
<div>capabilities.</div>
<div><br></div>
<div>Of course you can. Overgear it and you will overboost the engine.
Simple.</div>
<div><br></div>
<blockquote type="cite" cite>Also, both Opel and BMW have twin turbo
diesel engines in production<br>
that utilize a small housing turbo for low speed spool-up, then
kick</blockquote>
<blockquote type="cite" cite>in the larger housing unit for mid and
upper range powah. </blockquote>
<div><br></div>
<div>Taken from gas technology. These are sequential turbos. A smaller
one which bbosts at loower rpm and spools up more quickly, a larger
one to take over at higher rpm. Ideally you'd have 3 sequential
turbos... one for low rpm, one for midrange and one for high...</div>
<div><br></div>
<blockquote type="cite" cite>A supercharger is geared to the engine's
rotating parts, like a<br>
permanently mounted fan. They are notoriously hard on engines, for<br>
which reason VW is probably using a small one and since the drive
is<br>
direct, there's no lag.<br>
<br>
Turbocharging is a "softer" way to gain power by increasing
boost. It's<br>
a little more complicated than a supercharger, which is a simple
blower<br>
belted to and engine shaft. Turbocharging uses the flow of exhaust
gas,<br>
not the engine's rotation, to turn a fan on whose shaft is another
fan<br>
in the intake gas flow, so that when engine RPM is increased,
exhaust<br>
flow is increased, and therefore intake flow is increased and
fuel/air<br>
density in the head is increase for increase power.<br>
<br>
Turbocharging is easier on engines but has a lag as the turbo spools
up<br>
to speed. Sounds like VW is using a small supercharger--too small
to<br>
harm the engine but large enough to provide low-RPM boost--to
provide<br>
power in the sub-turbo operating range, then a larger turbo takes
over<br>
when the driver's foot demands it.</blockquote>
<div><br></div>
<div>Turbos are not softer on engines. They produce a huge amount of
excess heat, which is the enemy of any engine. Even intercoolers
oftwen are not enough. Heat buildup derived from turbos are notorious
for causing head-cracking in diesels.</div>
<div><br></div>
<div>Some other superchargers (the terrifically-inefficient Roots for
instance) also produce a lot of heat and ara hard on engines. Most
work only over a small rev-band.</div>
<div><br></div>
<div>From what I gather, the only charger which doesn't produce bulk
heat and which works over the full rev-band is the Lysholm
(twin-screw), the patents of which are held by the Aussie owners of
Sprintex. Supposedly these units don't even need an intercooler. They
are made under license by Autorotor and Whipple.</div>
<div><br></div>
<div>Turbos are not the best with diesels for another reason... they
only boost over a narrow rev-band, and when you rev past this boost
drops off and the turbo actually then strangles the engine... which
falls flat on its face, refusing to rev any higher. I would love to
try a Lysholm on my diesel Corolla (first fitting a bigger factory
turbodiesel, then replacing the turbo with the Lysholm). But I can't
afford it...</div>
<div><tt>--</tt></div>
<div>Andrew Grebneff<x-tab> </x-tab><br>
Dunedin<br>
New Zealand<br>
Fossil preparator<br>
<andrew.grebneff@stonebow.otago.ac.nz><br>
Seashell, Macintosh, VW/Toyota van nut<br>
<br>
HUMANITY: THE ULTIMATE VON NEUMANN MACHINE<br>
<br>
DEMOCRACY: RULE BY THE LOWEST COMMON DENOMINATOR</div>
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