I see another picture of cavitation damage, just inside the pump inlet.
    > The water boils due to the low pressure right at the suction
   opening and
    > along the face of the vanes.
    >
    > Coolant boiling temperature AND pressure determine boiling point.
   So an
    > effective system can loose pressure and begin to cavitate the
   pump. Even
    > stock engines can do this. In a cast iron housing it may take
   some long
    > time for this kind of damage to become obvious. In an aluminum
   housing,
    > damage can be sudden. The damage may eliminate some of the
   cavitation
    > through reducing performance, but overall system performance will
   suffer
    > from a reduction in GPM.
    >
    > Sharp edges should be removed from the pump cavity. This will
   increase
    > pump performance and raise the GPM where cavitation takes place.
    >
    > It is no accident that the lower radiator hose on every car is
   bigger
    > than the upper radiator hose. The lower hose is the water pump
   inlet. An
    > effort is made to provide coolant to the suction side of the pump
   at the
    > highest volume and pressure possible. This, so the /_minimum_
   /amount of
    > pump possible can do the job. Few cars have way too much water pump
    > installed from the factory.
    >
    > Raising the boiling point with a higher pressure cap setting helps.
    > Using higher boiling point chemicals in the coolant works.
   Slowing the
    > pump a bit works. And restricting pump output works. If the
   restriction
    > is down stream from the block, then pressure inside the block
   will be
    > slightly higher, and so, the boiling point inside the block.
    >
    > I use a 5/8" restriction on the outlet of the thermostat housing.
   I use
    > a 10% ethylene glycol and a bottle of Red Line Water Wetter. the
   crank
    > pulley is from racing beat, and is smaller than stock. We shift
   at 9,600
    > RPM. No cooling grooves in the rotor housing. No cavitation
   damage to an
    > aluminum pump and housing in 15 years of racing. No cracks around
   the
    > plug holes. Never an overheat problem. 244.8 HP at 9,400 RPM.
    >
    > Lynn E. Hanover
    >
    > Water outlet with 5/8" restricter welded on.
    > The clutch discs are Lamar Engineering/Tilton
    >
    > I would not use that disk on a street car as Robin would complain
   if she
    > had to drive it :) No springs.
    >
    > I suspect a lot of damage people attributing to caviatation is
   caused by
    > low water.
    > I can't imagines the Mazda engineers designing something that
   cavatates
    > inn our rev range.
    >
    > Paul Lamar
    >



   Lynn, how many pounds of pressure/cap?
   Steve Beckham

I use a 16 pound lever cap, but Stant makes caps up to 32 pounds.  *

Lynn E. Hanover



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