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Al
Al,
I wonder if you misunderstood the nature of the question
and
of my reply. I keep saying that I shouldn't reply to
messages
at 0-dark-30 when I can't sleep, but I keep doing
it.
Still, the question wasn't whether to convert or not
but
whether or not to use the controller.
Oh, I may have been
answering some combination of e-mails on the subject; but I thought some point
had been made in relation to power requirements and using the controller; or
maybe I was just blabbing
The belt-driven water pump has to be able to provide
cooling
flow under worse-case conditions: low-speed city
traffic.
Therefore, it is way over capacity at 6500 RPM.
This
can be mitigated somewhat by changing pulley sizes,
but
at the risk of the cooling at idle and taxiing.
Looking at the relationship
between speed, flow and power dissipation, I come to a different conclusion. The
pump output curve goes up relatively linearly with speed and bends over
toward flat as the back pressure builds. The power dissipation required
(with a prop) goes up roughly as the cube of the speed (parabolically), so it goes
up slowly at first and then heads up pretty steep as you get past 3-4000 rpm. At
some point out there the curves for flow produced and the flow required cross,
and beyond that you have a cooing problem. So the greatest excess flow
with the belt driven pump is probably somewhere in there around 3000 +- (where
you probably don’t care if you are wasting a couple of horses), and at
the power output at 6000-6500 needs all the flow you get; and then some if you
have marginal cooling capacity.
The electric pump allows demand-based flow, using only
as
much energy as necessary to provide adequate cooling at
that
moment.
Not using the controller, leaves three basic options:
(A)
wire direct, pumping full flow all the time and using
a thermostat to maintain minimum heat.
(B)
wire direct, with no thermostat, and run cold during
decents and other low-load conditions.
(C)
Put in a manual speed control.
Rusty's
concern - inadequate "minimum" flow speed - can
be
dealt with fairly easily.
I’d go with the controller. Probably at cruise
the EWP can save a bit of pumping power.
Al