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Water Pump Cavitation

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I used to do some club racing with my 1980 RX-7 (12A Rotary) and one of the aftermarket components I bought was an undersize main pulley. This aluminum pulley was advertised to reduce water pump and alternator rpm, thereby reducing water pump cavitation which can occur during high engine rpm (I guess the stock water pump was designed to pump water at relatively low street use rpm's).

I noticed that Al Wick's Subaru powered Cozy was having some initial trouble with entrapping air in the cooling system, and he runs in the 4000 to 4500 rpm range. My subaru Impreza never has any entrapped air but I don't sustain rpm's any higher thant 3500. I wonder if Al's water pump is cavitating. I may ask him.

When I am ready for my water cooled engine, I'm going to look into reducing water pump and alternator rpm's so they match their respective stock rpm's at 60 to 70 mph (on the street) in top gear. Not many engines actually sustain rpm's of 4000 to 7000 rpm while in their original car body, even if it won't hurt them at all. Has anyone here done this or planned for this? We use pumps ALOT at work, and the efficient rpm range for centifugal pumps is relatively small. Its been bugging me for awhile.

Andrew Anunson

I work underground and I play in the sky... no problem

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I believe some have used undersize pulley's to slow doen the alternator, although I think the problem is more at the high-end - 8000 + that we don't get near.


There's a lot of talk and some testing of electric water pumps going on on the flyrotary list. I'm waiting for the results on these tests.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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I'm pretty sure that by the time I get an engine mounted, the electric water pumps will rule. I'm interested in John's radiator fan system too. Those components could be set up to do post flight cooling and reduce cowl exposure to heat soaked engine.

...Destiny's Plaything...

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