NEVER restrict the inlet side of a hydraulic pump!!! That will destroy the pump!!!

When you cut coils off the relief spring, all you are doing is making the system operate at a lower pressure. You are changing the pressure relief valve. Messing with the relief valve can be very dangerous!!! Some systems use a simple one spring poppet type relief valve like oil pumps. Other systems use a piloted relief valve that has a small poppet valve controlling a larger valve.

PS pumps are very simple things, they do not have variable delivery. They are fixed volume pumps that put out just so many cubic inches of fluid every revolution. When the steering wheel is not being turned in most systems the pumps are pushing their fluid output over the relif valve which builds heat. These systems run HOT so anything you can do to cool them helps!

There are some variable assist pumps that have electric solenoid valves to select relief valves. There are also some that have an orifice in the primary relief valve that increases the pressure with rpm's. We would have to go into some HD hydraulic theory to tell you how that works. You can get fluid power training thru many industrial/mobile fluid power distributors.

The amount of assist you have will depend on the system pressure.

If you restrict the output of the pump it will not affect system pressure but it will make the steering "slow" and will require more effort for fast motions.

Power steering pumps "whine" when:
-The shaft bearings go bad.
-The pump has air in the system causing cavitation. This can be caused by low fluid levels or a restricted pump inlet. This will quickly destroy a pump.
-The pump develops scratches in the valve plates inside the pump that allows fluid to directly bypass from the high pressure side to the low pressure side of the pump.

ANY TIME YOU WORK ON THE POWER STEERING SYSTEM INSTALL A FILTER in the return line from the PS control/gears back to the reservoir.

From my files:
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WIX TRANSMISSION/PS FILTER #58964
200 PSI WORKING, PRESSURE RELIEVED, MAGNETIC
CHANGE YEARLY OR 12000 MILES
FORD EQUIVALENT FILTER KIT #XC3Z-7B155-AA
FILTER ALONE #XC3P-7B155-BA