Oil pump shim and pressure question..
 

How does shimming the spring in the pump increase pressure......here is why I ask: the spring is there to keep the bypass valve closed so all the oil goes to the motor when the pressure reaches a certain point to over power the spring it opens and bypasses oil.....so lets say the spring opens at 60psi.....the pumps oil pressure doesnt change by adding a shim....it would only keep the the valve from opening.....it now may open at 70psi..........

Please stick to the topic....I know volume is more important than pressure....etc, etc......

I want to know how shimming the spring could possible increase oil pressure at idle......

Thanks Tom

It changes the spring's install height/length. A spring's pressure increases as you compress it until it hits a certain compression, so it now takes more oil pressure to overcome the spring pressure and lower the plunger.

Shimming the spring does not make the pump, pump harder, it basically changes the relief valve pressure/bypass valve pressure (which ever term you want to call it).

I can only imagine that there is a little bit of bypass even at idle. I noticed a 10 psi increase in pressure when i went to a .120 shimmed pump.