I remember a discussion on speed of water moving through radiators and
whether it is better for it to move slow (more time to exchange) or fast
(higher gradient).
There is an excellent discussion in June 2001 Circle Track.
The gist is that they use a pump capable of about 100 gal per minute. Due to
restrictions in the head and radiator this nets about 60 gal per minute for
the system. The excess capacity raises the pressure in the system cutting
down on boiling in the restrictive hot spots.
It was also pointed out that racers pay a lot of attention to locating hot
spots in the heads and if possible opening up flow there by opening
restrictive passages or putting in extra entry points to increase flow of
cool water in those locations, trying to keep the head temperatures between
180 and 210. The old rule of thumb (slowing down the flow) is being replaced
by faster flow rates because turbulent flow exchanges heat more efficiently
than laminar flow.
At the same time they point out that to much of a good thing is bad. The
engine develops power by gas expansion and you develop more power at higher
temperatures.
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