I would say use what the guy who built the engine said. He must know where you live also. He set up the tolerances so...

 

20W50 is way too heavy. 10W30, or 10W40 if you want a little thicker oil.

 

Guys,
I have a 383 stroker from the engine factory. they told me 10W30. Thanks
John

I would use the viscosity the builder suggested.

 

X3 on the 10W30

 

Thanks guys
John

 

I have a new 383 as well and my builder has me running rotella 15w40 which he says they run in all their 383's. motor seems to like it, tons of oil pressure.

 

Pressure doesn't mean flow. That engine isn't all that different from your heart... high flow is better than high pressure.

I'd go 10w30

 

10w30 for sure

 

URE built my 383 and told me to use joe gibbs hot rod 15-50

 

I run Rotella T6 5W-40 in both my '69s and my '02.

 

20/50W is to heavy. Start with the 10W30 and see how it works and where your oil pressure is at. Prob can get away with a good 5W30.