Here is the data at 4300 RPM for the stock Mazda water pump. No pre pressure.
Pressures in psi. Pump outlet, flow meter, inlet respectively.
Flow in gallons per minute.
Flow Press 1 Press 2 Press 3
Closed 10 10 2
15 5 5 2
20 5 5 2
25 5 5 2
30 5 4.5 2.5
35 5 4.5 2.5
40 4.5 4 2.5
45 4.5 3.5 3
50 4 3 3.5
stopped 3 3 4
The water heated up some so the final pressure was higher
than the initial pressure.
Obviously if you are looking to up the pressure in the block by adding
a restrictor you are barking up the wrong tree. All you would be doing
is cutting the flow. This may or may not be good depending on your goals.
Our main goal, assuming the metal is adequately cooled, is to prevent
boiling.
Less flow may mean lower water temp but higher cylinder head temp
for lack of a better term. Nobody, and that includes me, have measured the
temperature in the rotor housing within 2 mm of the combustion chamber.
So far that has not proved to be a problem in the Mazda as I can not
detect any deterioration of the rotor housings in this area due to overheating.
Yes the rotor housing shrinks if over heated but I am not sure if increased
water flow is the answer. Usually this happens when the engine runs out of
cooling water or the water level drops below the pump intake and the pump sucks
air.
If you are running a restrictor and you are happy with the cooling you can
achieve the same thing by slowing the RPM of the pump and probably suck less HP
to drive the pump in the bargain.
A piston engine with an aluminum cylinder head is another matter. They do indeed
show signs of failure if inadequately cooled due to inadequate flow of cooling
water. And that goes for the exhaust valve in spades.
All these tests confirm the proper place for the expansion tank and pressure cap
is between the rad and the pump inlet to delay boiling. Not between the block
and the rad as is common on passenger cars. The pressure in the system on average
will be much higher. I think placing it between block and rad is traditionally
done on passenger cars as it is a convenient place to put the expansion tank and
pressure cap. In our case with the rad frequently mounted under the engine it
does not matter where the tank is plumbed in.
Now having said all that a bit about the ability of a rad to withstand higher
pressures. A wide thin tube wants to deflect towards a cylindrical shape
when pressurized. It is therefore better to have two rows of narrower
tubes with the same over all rad depth.
Paul Lamar
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