Phil, I have a GPAS 2180 VW and also use 15W40. I did two things to raise the OP, 1, Installed a Heavy Duty oil pump. 2. installed a adjustable oil pressure relief valve.( Probably similar to yours) and adjusted the oil pressure up until I got 13psi at idle with the engine temp at normal operating temp, about 200 to 214 deg. I also added a remote oil filter. Idle speed is about 950 to 1000 RPM. Any lower and the engine wants to lob.(Redneck term for idling rough) I'm running an Ellison EF2 throttle body and Compufire Electronic ignition.
