J.P.
Sorry for going off. It was not you I was after but all of the other folks out there that read these post. I see the same question about pressure all the time and it just got under my skin this time.
Now back to trying to help.
20w-50 "should" flow like a 20 weight
oil but lube like a 50. I have never been much of a fan of multigrades in performace engines. The straight grade will hold the same weight across the board and thus should hold the pressure the same after warm up. Plus the heavier
oil will in my view do a better job of staying put. Try it you have nothing to loose and it my help your problem.
The pump will control the max pressure you will see by way of the valve built into the pump. Again if however the engine is built on the wide side it will take more
oil to full the space and thus more volume will be needed.
Just for the record I am no fan of syntetics. Sorry. I am still waiting to see a side by side done for wear at 1,000 hrs to show me if one is really better than the other. In 20 plus years I am still waiting.
I run straight 40 in all of the perfomance engines I build and have never had a failure.
We can talk about this more if you like. Just give me a call at my shop and I will try to get into more detail if needed.
407-857-8587 Mon-Fri 9:00-5:00 est.