Fresh 427 s/o 40psi oil pressure drop

[Ze Colonel]

I have a windsor but my experiences are similar and I thought I might share thejm.

My motor was build by a well known engine builder for fords on this site. My oil pressure is 40 to 45 psi when warm and engine speed above 2000 rpm. This seems low to me as I expect 60 psi or better on a fresh professionally build engine. Old rule of thumb is 50 psi plus 10 psi for every 1000 rpm over 5000 rpm. I have 60 psi when cold at idle no matter what oil.

My build shteet says 0.0035 inch clearance on mains which is 0.0005 over stock maximum allowed. I have a 25% high volume pump and have tried 5-30wt up to 20-50 wt. The number I site are for 20-50 wt. The engine builder did not seem conserned about the oil pressure or the bearing clearance and suggested I turn up the pressure relief valve spring.

As a mechanical engineer this did not make sense to me so I called Melling tool company about their pump. They agreed that turning up the relief setting would not improve pressure once warm.

I have chosen to stay with the 20-50 and just drive the thing and not worry about it.

I would like to know what others expect and have for oil pressure once the motor is warm and at speed. I suspect my old rule of thumb has no engineering basis and that anything over 40 psi for a motor that stays under 7000 rpm is not a real problem other then it bothers some of us ( including myself ) to look at the gage and see lower then expected oil pressure on an expensive motor.

How about 0.0035 main bearing clearance? Why would a compentant engine builder purposely install such clearance on a street/strip motor? I do not know but it sure runs good......