The stock (rear) oil pressure regulator is designed to bypass at
60-65psi of oil pressure.  As an upgrade, Racing Beat offers
an oil pressure regulator rated to bypass at 80-85psi of oil
pressure.  This is recommended for street and mildly modded
FC3S.  As a side note, when you do upgrade to a higher rated oil
pressure regulator, you need to "shim" the front oil pressure
regulator, located on the front cover, with a few washers; the
Racing Beat units do come with instructions and the proper washers
for this.
The higher oil pressure is needed for higher oil lubrication needs
for more powerful engines.  The rotor and stationary bearings
are grooved, journal-type bearings.  Oil helps to float the
rotors and eccentric shaft (respectively) to keep them moving
smoothly.  Increased power output from the engine means more
force transmitted to the bearings.  With the higher oil
pressure, this keeps the bearings lubricated and cool.  Oil
is an important fluid in keeping the engine cool.  Mazda
engineers estimate the engine oil contributes to 1/3rd of total
engine cooling!  The higher oil pressure circulates oil faster
for more efficient lubrication and cooling.
Racing Beat offers a higher rated 100-105psi rated oil pressure
regulator for race-only application - do not use this on
a street car, as it can causes excessive smoking and blow-by. 
A stock FD3S oil pressure regulator should NOT be used on a
street FC3S, because it is also rated to bypass at about 100psi of oil
pressure.  The stock FD 13B-REW motor has reworked oil passages
and bearings to efficiently use the higher oil pressure - the FC3S
does not.  Don't use these higher oil pressure regulators on
an FC3S motor unless for racing use only.
Questions?  Comments?  Send email to: 
reted@fc3spro.com
03/13/2004