Date:         Wed, 28 Sep 2005 07:58:29 -0500
Reply-To:     Jim Felder <felder@KNOLOGY.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jim Felder <felder@KNOLOGY.NET>
Subject:      Re: yet another engine choice - VW "twincharger"
In-Reply-To:  <a06002008bf601aa852d5@[218.101.117.80]>
Content-Type: text/plain; charset=US-ASCII; format=flowed

>>>
>>>
>
> Yep... and they don't even know what a supercharger is. A
> supercharger AND a turbo? A turbo IS IS IS a supercharger!
>

A supercharger is geared to the engine's rotating parts, like a
permanently mounted fan. They are notoriously hard on engines, for
which reason VW is probably using a small one and since the drive is
direct, there's no lag.

Turbocharging is a "softer" way to gain power by increasing boost. It's
a little more complicated than a supercharger, which is a simple blower
belted to and engine shaft. Turbocharging uses the flow of exhaust gas,
not the engine's rotation, to turn a fan on whose shaft is another fan
in the intake gas flow, so that when engine RPM is increased, exhaust
flow is increased, and therefore intake flow is increased and fuel/air
density in the head is increase for increase power.

Turbocharging is easier on engines but has a lag as the turbo spools up
to speed. Sounds like VW is using a small supercharger--too small to
harm the engine but large enough to provide low-RPM boost--to provide
power in the sub-turbo operating range, then a larger turbo takes over
when the driver's foot demands it.

Jim