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