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In a message dated 10/13/2007 5:37:19 P.M. Eastern Daylight Time,
lendich@optusnet.com.au writes:
quite the surprise. Japanese engineers are expert at making
sure the design has extra safety margin. Even back in the 70's. Although they
are much better at it now. I can't imagine they are rpm sensitive 33 years
later.
I have heard of a lot of guys adding flow
restrictions on pump inlet, not aware they are increasing pressure drop.
Particularly true with fuel systems.
-al
wick
Choking the inlet side of a centrifugal pump is a sure way to get
into trouble. Same as out of tolerance suction lift. Notice that the exit hose
from the radiator is larger than the inlet hose.
My pump outlet has a 5/8" hole restrictor on the outlet. Same two water
pumps for 9 years. Shifting at 9,600 RPM. No cavitation damage at all. Generally
the radiator(s) will be enough restriction to keep the pump well below its top
flow rate, and lowest inlet pressure. If there is little or no restriction on
the outlet side, the pump might cavitate momentarily during acceleration.
More likely with lower total system pressure, and low restriction. Less
likely with an accumulator system and more restriction,and higher system
pressure. Less likely with low system volume. More likely with high
system volume. With just a bit of anti freeze and its anti foaming agents,
very unlikely. More likely when air remains in the system. The pumps are
mounted high on the block, and will not pump at all with a bit of air
sitting in them. It is critical that the pump be submerged prior to start
up.
Lynn E. Hanover
Lynn,
Just to clarify! - Is that with standard pulley sizes?
George ( down under)
Stock pump size and pulley ratios are selected to allow day long
idle in Death Valley with the air conditioning running. Radiator designed
for maximum flow rates sufficient for day long full throttle runs across Death
Valley with adequate cooling, without cavitation. I have never seen a pump
damaged in any race car in
40 years. I bought a maroon Buick 4 door from a local pump company
for $400.00, that had the sad GM 3.8 liter V-6 with very low oil pressure and
the ends of the pump impeller blades chewed off, and a collapsed lower
radiator hose. No spring reinforcement installed. Every time it came to idle the
oil pressure idiot light came on. The tappets would bleed down and it would
clatter like crazy. Then it would overheat. It was a salesmans car and had
nearly 100,000 miles on it, but looked and smelled new. NAPA had a pump
extension kit for the 3.8 and 4.2 V-6s for $25.00 that doubled the oil pump
volume. A new lower hose and a rebuilt water pump, and I gave the mighty Buick
to Good Will with 206,000 miles on it. It still looked and ran
good.
Unless a blockage develops between the radiator(s) and the engine,
you will never see cavitation or pump damage at aviation RPM with nearly any
drive ratios. Slowing the pump with smaller crank pulleys probably only
endangers idle heat control. And not much even there. It might add one or two HP
at cruise.
Lynn E. Hanover
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