Ok another questions, " what if your motors have over 600 hours on them?

is it better to run synthetic if your running hard all day?

Don't believe everything merc says....and they don't make oil !

All the more reason to run Synthetic

At that point I would continue to run whatever has been in there.

I posted once before,, My company builds testing labs and we built a lab for ______corporation (can't mention) they are who grades and cerifies that the oils meet certain spec's. Cool place with 100's of engine test beds, you name it they had it and just about any condition you could put an engine through, Ice, heat, salt, everything.. Obviously I asked what the best oil was to run when we were at lunch one day.. He could'nt answer me but told me to rephrase my question... So I thought for a bit and asked "What oil do you use" he said aaahhhhhh Valvolene Racing oil only in everything they own,,,
Some oils meet spec or guidlines and then there are some that exceed all..
I've used Valovolene 20-50 racing oil in all my toys,,
For whats it's worth some studies have shown Synthetics casue loss of RPM's due to windage.. Pays to know the MAN...LOL..

What is acceptable Oil pressure on a stock motor at High RPM and what should it drop to at idle? I can run 40PSI at high rpm and when it drops to idle on after a longer run it can drop to 10 psi at idle. Running 10W40 Amsoil? I been told to run anything from SAE 30 to 20W50. 502 Motor.

That sounds pretty normal for a stock motor. I think the manual states that as low as 6 psi at warm idle is OK.

That would be Valvoline Racing Oil "not street legal". The other two Racing Oils are low on Zinc. The "not street legal" has a full complement of zddp, thus needs no additives, like the old GM EOS.

Mercury Racing does not recommend Synthetic motor oil.