Dont use them if you are building street motor,rollercams, especially mechnicals, need sufficient lubrication when driving low engine speeds(idle,etc).Hydraulic rollecams wont work at all with restrictors!!!
Restrictors are mainly used in race-engines witch sees lots of high rpms,so there will not be so much oil in cylinderheads or liftervaley,more in oilpan.
I use the ones that screw in the rear oil galleries in my 406, they had a tiny hole (.030" I think) so I drilled them out to .090" to allow a little more oil up top to cool the springs and such really simple to do and no dramas yet.
WHAT YOU NEED TO DO BEFORE RESTRICTING AIRFLOW IS DECIDE WHAT YOU WANT TO DO IF IT IS A STREET/ENDURANCE RACE CAR RUN IT TO SEE IF OIL PUKES OUT THE BREATHER IF IT DOESN'T YOUR FINE. IF IT DOES YOU NEED RESTRICTORS. 1/4 MILE CARS DO NOT NEED RESTRICTORS BECAUSE IT IS SUCH A SHORT DISTANCE IT WOULD BE POINTLESS TO RESTRICT OIL FLOW. INSTEAD OF USING RESTRICTORS I WOULD JUST USE A STANDARD VOLUME OIL PUMP AND MAKE SURE YOUR CLEARANCES ARE WITHIN TOLERANCE LEVELS AND YOU SHOULD BE FINE. YOU NEVER WANT TO RESTRICT OIL UP TO THE SPRINGS IN A ROAD RACING ENGINE BECAUSE THIS IS ONE OF THE HOTTEST PARTS OF THE ENGINE. WHAT ELSE COOLS DOWN THE FRICTION?
Sidebar to the above post - Ferrari engines have been designed since day one with the exhaust valves and at least half of the spring height totally submerged in oil at all times to carry off the heat; that's why old Ferraris with worn valve guides smoke so badly! Even today, they run normal oil pressure of 85-90 psi hot through 18mm (3/4") lines - that's quite a flow rate. Ferrari has always used the oil system as part of the engine cooling system, as nothing else can cool the stems and springs.
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