> That makes sense.  But I got to wondering as to exactly what conditions
the pump
> _and pulley!_ were designed around.  What if, at 5000 or more rpm at
cruise, we
> have more capacity than we need, and end up pumping a lot of back pressure
> against a partially closed thermostat.  A scenario like that would be
wasted
> power.  If that were so, and we just put a larger pulley on the pump, it
would
> not absorb as much power, and the lower pump rpm would better match
> requirements.  How do we tell if a water pump/pulley configuration is
wasting
> power trying to over achieve?  Has anyone tried a larger pulley (less pump
speed,
> less power drain, less flow, but still plenty sufficient for the
application)??
> Tracy, are you out there??
> Inquiring minds need to know .... Jim S.
>

I use an underdrive pulley (smaller than stock) on the crankshaft  which
slows the pump down.  The real reason I use it is to slow down the
alternator.  Cooling is still good but I noticed a  *very slight* decrease
in cooling system performance when I went to the smaller pulley.  This is
only noticable in climb on a hot day.

In general, I think the pump speed & performance with the stock pulley is
well matched to engine requirements and this is what I will use on my 20B.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com