oil pressure falling after rebuild ?

[gramos]

I rebuilt an austin healey engine recently , new main and big shells , thrusts , pistons , followers , rocker arm bushes , pressure relief valve and spring ,
rebuilt oil pump , cam , cam bearings , new ali cylinder head , basically everything that needed doing after a cam follower and cam lobe failed .
when cold on start up I have 80 psi which drops to 60 + when warm . After 2 hours driving with 50 + lbs on the gauge at 2000 + rpm
it drops to 10/ 15 lbs at idle !
This has me a bit worried as prior to rebuilding it always had 25 psi at idle , which is what the manual states as normal .


the engine has just reached 500 miles so drained and good classic car spec oil was put in plus a tin of STP .

What could be the cause of this falling pressure , ?

the crank was checked and polished to within minimum specs and ovality .
oil / water gauge has been rebuilt with new capillary tube,

all suggestions welcomed , thank you .

[GreenV8S]

New pressure relief valve and spring?

If so, are they identical size and rate to the old one?

[stevieturbo]

Assuming pump/filter/relief are all ok, It would seem various bearing tolerances have increased during this rebuild. Either deliberately, or not.

Could be mains, big ends, lifters, they all add up, and it doesnt take a lot to make a difference.