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.

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