> All speculation and theory so........ does anyone know the
> advantages/disadvantages of 4 vs 6 vane?
Water pump design is an extremely complicated topic, even for a pump running at
constant rpm, let alone with the widely varying rpm,
head and flow parameters that are inherent in automotive cooling systems. And
the number of vanes is a relatively minor variable in
the performance of the pump. Things like vane shape, clearances, housing shape
and so on have a much larger effect on results. So,
my opinion is that it is impossible to state categorically that a 4 vane pump
is better or worse than a 6 vane.
In other words, this discussion is futile, until and unless someone gets a
sample of each specific pump and does some specific
performance tests on it. Even then, it is going to be hard to say which is
"better", since I've never seen any evidence that lack
of water flow is a problem with our engines.
One thing, though, there is no such thing as "moving the water too fast so the
radiator can't cool it". A long-persistent myth,
perpetuated by those who slept through high school physics (or took auto shop
instead). What can happen on cars with the pressure
cap on the high pressure side of the radiator (like the TR2-6) is that the
pressure differential across the radiator rises so high
that the cap opens and lets coolant blow out the overflow. THEN the engine
overheats, due to lack of coolant flow (and coolant).
I've also seen non-TR engines where the hose on the low pressure side would
literally suck closed, blocking off the flow.
My own experiments with 4 vs 6 (on a TR3 motor) showed no measurable difference
in cooling performance. But I didn't bother taking
any flow or pressure measurements. With a stock 4 vane pump, and adequate
airflow through the radiator, the engine stays cool even
in 115F weather (which is more than the driver can stand).
Randall
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