Oil viscosity - why the 20W-50 BS?

I ran my first 340 with 20/50 because i had too! hot idle oil pressure was low.
My 2nt 340 i built better, oil pressure would peg my 80 psi gauge when cold and idle hot at 30 psi. Ran it that way for 15 years, no problems.

The last 3 year it's been running on syn 5w30.........idles better drives better, and picked up several ten's in the 1/4 mile......
Motor is tired now and will be retired this year for a stroker.

NO the light oil didn't ware my motor out......it's just 17 year old and i don't want to throw a rod thru a .020" over 340! LOL

If i live in a 100+ degree climate, i would still us a 20w50......If not, us as thin of oil as your oil pressure (aka You) is comfy with.:director::D