recomended oil for 350 ???

[87droptop]

Hi all,
what is the recomended oil grade for a 350 ( 1968 old  engine, now 383 full rebuilt) ??? i put 10w-30 to run it in, when i left it on for more than 20 minutes i started hearing what initially sounded like vibration, then more like few lifters tapping nearly at the same time, as that happened the idle would drop 100-150 revs, i shut it off. this was not the first time i start it, but the only time i let run this long. next day i started it and it was fine again, i ran it for about 12 minutes only... i guess the oil got hot enough to thin down and cause that noise.... there is no other logical explanation. can anyone shed some light please???
Thank you all again..  

[gtc]

So, since the rebuild it's still a low mileage engine?

Does it run hot?

How's the oil pressure when the engine is hot?

Not sure about a 383's requirements under Oz conditions, but 10w30 sounds a bit narrow to me.

I run Penrite HPR40 (25w70) in a 454. It's a mineral oil without any friction modifiers.

[Scott]

A 20w50 is the standard (so to speak) oil that would be in most sbc's so I wouldn't stray too far from that.  A semi synthetic, or full synthetic oil would be preferrable but only after the engine is properly run in. 10w30 is really too light for a chev, enpecially in Australia.

[Thunder Kiss]

If you're running a flat tappet cam, Penrite do a high zinc 20W50 called Classic Light.

[87droptop]

thanks 4 the info guys. the engine just only got started few time since rebuild. have not driven it on road to run in. oil pressure is initially at 70 ( max), engine does not run hot, under half way. when it gets warm, just under half way, pressure drops to about 40-45, which again is an indication of oil thinning a bit too much.... i think i will try 20w-50 in that penrite. it did occur to me that back 42 years ago, there was no oils in the category of 10w-30, etc... all they had was 20w-50.....
cheers.

[Scott]

If it is a fresh engine, then do not use a full synthetic. They are too 'slippery' and may stop the rings from bedding properly. Talk to the engine builder and ask what he recommends.