Alex Rodriguez wrote:
> In article .com>,
> says...
>
>
>>I thought a supercharger was demand based, i.e. not running at light
>>throttle openings
>
>
> No, that more accurately describes a turbocharger. Until you get enough
> exhaust gas flow, it is basically doing nothing. To get more exhaust gas
> flow, you need to step on the throtle some more.
>
> -----------------
> Alex
>
Centrifugal gear driven superchargers also had very little boost at low
rpm. Positive displacement ones such as Roots and the GMC style gave
boost at all rpm.

There were also some engine driven chargers that had a complicated drive
mechanism that did respond to throttle position in terms of speed of
charger. These were for street machines. I think there was a clutch
that either kicked in, or speeded up the blower speed on higher throttle
openings.