It really depends on HP/torque of the engine. The Turbo Action VBs are around 105 psi, Griner Engineering 140-220 psi. Of course the more pressure, the more load on the pump. If you have a high torque engine, I would set it to around 175 psi, especially with the 904 with small surface area clutches. Lower torque engines, use 105-140 psi.