Tracy Crook wrote:

Paul Lamar wrote:

The area of the water
outlet passage just below the upper most bolt boss is
even worse at about .66 square inches. IMHO this is one of the major

reasons

why the Mazda pump cavitates at only 8000 RPM and flows so little
water when it is not cavitating. See the picture below of the pump with
the upper part cut off and the water passages ported as much as possible.

It makes no sense to have a hole in the block with 3.25 square inches
and then have a restriction in the pump of .66 square inches.

The neck-down to .66 sq inches might be excessive (although I have seen no
evidence of too little flow in my installation) but it will not cause
cavitation.  In fact, restriction on the outlet REDUCES the chances of
cavitation.  This is why car racers in the earlier days got more overheating
problems when they removed their thermostats.  The drop in outlet
restriction caused the pump to cavitate.

Also note that the combined area of my two 5/8" cooling hoses is only .61 sq
inches. and this is a much longer path than the 1 inch or so in the pump
outlet.

Tracy Crook
rws@altavista.net
www.rotaryaviation.com

I am not sure I agree with this Tracy. You have a closed loop system here.
A restriction anywhere in the loop will cause problems. Worst case
scenario of course is the loop plugged completely. I guarantee cavitaiton 
under those conditions. Even in an open loop system if you plug
the output of the pump it WILL cavitate. Obviously there is some 
minimum size of a hole required as a function of the RPM of the pump.

To clarify things it is ABSOLUTELY ESSENTIAL TO RUN THE STOCK MAZDA
THERMOSTAT UNLESS YOU PLUG THE BYPASS!!!! THE HAYNES MANUAL IS WRONG
ABOUT THIS!!!! REMOVING THE THERMOSTAT WITHOUT BLOCKING THE BYPASS
IS GUARANTEED TO CAUSE OVER HEATING in a Mazda rotary.

You live in flat country too Tracy :-) I want to make sure my 250 HP 
turbo engine cools when climbing out of the 110 degree F desert at or 
below sea level and over a 12,000 foot mountain against a 30 kt headwind.

Paul Lamar
 
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