I have twin 540's in my Formula. had them both apart last winter for repair. One recieved a new block, pistons, crank turned and rods.
The other had the crank turned, bearings and rods.
I started them both up on the stand, but did not dyno them. The first time out, they both ran fine, both had 60 PSI oil pressure when first started.
After warm up, at about 4700 RPM, the engine that did not recieve the new block, lost oil pressure to about 40 - 45 PSI while the other remained at 60. When the throttles were backed off, the oil pressure came back up to about 50 PSI. I checked oil for water, and level, both are good. Does not seem to make noise or knock, so I don't think it is a bearing. Any one have any ideas ????
Thanks

More than likely, the engine that experiences the pressure drop has more main bearing clearance than the other.

try a mechanical gauge.. but at lease its around 45

If the oil pressure really drops a lot after a long hot run then you probably have a bit of excessive clearance on that engine and may have some cause for concern, but if it stays around 45 its not too bad.

Also the two gauges could be as much as 10% off from each other so its a little difficult to directly compare the two. I would get a decent mechanical gauge and verify the electric one before I went too much further...