Pontiac recommends straight 30 or 10w40 for the Ram Air engines that has the crank grinded .001" smaller than std, .0055"-.0061" piston clearance, deleted oil shields on valve springs and 3.73:1 - 4.33:1 rear gears, instead of straight 20 or 10w30 for a std engine.
No Xw50 oil ever unless you´re in Death Valley or running NASCAR.
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1966 GTO Tri-Power
1970 GTO TheJudge
http://www.poci.org/
http://gtoaa.org/
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