Thanks for your reply mate
My other magnum engine and a friend with a magnum engine have average or pressure of around 60 PSI at full throttle and 40 at idle so there does seem to be an issue with this engine.
It's a complete standard magnum bottom end. With standard crank bearings and rods. I used to run the standard roller lifters and still had oil pressure problems but now I run solid lifters and cam. I contacted a Mopar performance engine building shop and they said they could do some oil modifications for me that would improve oil into the bearings but probably would not improve oil pressure.
