Reply to "double water pumps."

To clarify the point of my first post, additional slowing of the Pantera's water
flow to improve cooling (for instance further under-driving the water pump)
would likely only make things worse.

To increase the flow rate, there are several approaches that
might work. In addition to adding an auxiliary pump, you can increase the
pulley ratio but that may lower the cavitation RPM. You can also add a backing
plate or use a water pump with tighter tolerances or larger impeller or you
can use a water pump with a curved vane impeller. Properly executed, the
latter also has lessens the tendency for cavitation at higher RPM.

I intended to ask Forum member Mid-Engine Mike to share
his experience with installing a custom diameter pulley to
change his water pump speed and then follow up with why his approach
might work with one type of radiator (or pump) but not with another. It's
important to understand that mechanical automotive water pumps are not positive
displacement with a linear output. They are centrifugal pumps (like a
turbocharger) with a non-linear output. Also, multi-pass radiators present
a non-linear flow restriction. The restriction in going from a 2 pass design
to a 3 pass is much higher than going from a 1 pass to a 2 pass design. The
modern trend is to use a single pass radiator but there are times when the
increase in restriction of 2 pass design is beneficial (e.g. leads to higher
system pressure which eliminates boiling in localized hot spots).

Often a poster will be presented with multiple seemingly conflicting options
that he needs to choose between. One person says to increase the flow rate,
another says to decrease it, a third says to reduce restriction. All of these
may work in particular instances but, without understanding why and when they
work, it's little more than a guessing game. When you understand the basic
principles you can at least increase the odds that a particular solution
will work for you. For instance, it's easy to see why the stock Pantera
under-drive pulley which slows down coolant speed might work with the stock
dual pass radiator which offsets the effect by increasing coolant speed but
might present a problem if you switch to a a single pass radiator which does
not.

Dan Jones