best type of oil for 71 340 engine

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I live in a warm climate and use AMSOIL 20w50 Z-rod which contains Zinc.
 
I live in a warm climate and use AMSOIL 20w50 Z-rod which contains Zinc.
Ya, zinc goes without saying in a flat tappet engine. If you run a roller you can run pretty much anything. Weight depends on the bearing clearance. I keep it simple and run Valvoline 10/30 conventional and some zinc additive.

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I'm surprised there's only 27 responses in 10 years. Folks are tired of answering the question! There might be some wrong answers but no right answer. LOL
 
I really like the Joe Gibbs Driven oil. 10w-30 is what my engine builder told me to use.
 
In my Hi Performance 340 I am running Pennzoil 10W-40 with a can of STP at every oil change and 20k miles later engine is still running strong with no problems....
 
i ran royal purple 10-40 xpr synthetic for 9 years on my 70 340 never a problem when torn down to add new alu heads and check **** out at 7,000 mile it looked new inside almost no wear on any of the parts . i added zzdp the first 3 oil changes nothing after that ,
let me add every engine is different no idea how yours was built , just stating my experience
 
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